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Papers by Daniel Antonio

Lawrence Berkeley National Laboratory, Nov 18, 2004

We present neutron diffraction, magnetic susceptibility and specific heat data for a single-cryst... more We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu 3 Au structure) compound Pr 3 In. This compound is believed to have a singlet (Γ 1) groundstate and a low-lying triplet (Γ 4) excited state. In addition, nearest-neighbor antiferromagnetic interactions are frustrated in this structure. Antiferromagnetic order occurs below T N = 12K with propagation vector (0, 0, 0.5≤δ) where δ ≈ 1/12. The neutron diffraction results can be approximated with the following model: ferromagnetic sheets from each of the three Pr sites alternate in sign along the propagation direction with a twelve-unit-cell square-wave modulation. The three moments of the unit cell of 1 µ B magnitude are aligned so as to sum to zero as expected for nearest-neighbor antiferromagnetic interactions on a triangle. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12K, there is a transition near 70K below which there is a small (0.005 µ B) ferromagnetic moment. There is considerable field and sample dependence to these transitions. The specific heat data show almost no anomaly at T N = 12K. This may be a consequence of the induced moment in the Γ 1 singlet, but may also be a sample-dependent effect.

Bulletin of the American Physical Society, 2017

Submitted for the MAR17 Meeting of The American Physical Society On the nature of the phase trans... more Submitted for the MAR17 Meeting of The American Physical Society On the nature of the phase transition in uranium dioxide 1 K. GOFRYK, INL, D. MAST, INL, UNLV, D. ANTONIO, K. SHRESTHA, INL, D. ANDERSSON , C. STANEK, M. JAIME, LANL-Uranium dioxide (UO 2) is by far the most studied actinide material as it is a primary fuel used in light water nuclear reactors. Its thermal and magnetic properties remain, however, a puzzle resulting from strong couplings between magnetism and lattice vibrations. UO 2 crystalizes in the face-centered-cubic fluorite structure and is a Mott-Hubbard insulator with well-localized uranium 5f-electrons. In addition, below 30 K, a long range antiferromagnetic ordering of the electric-quadrupole of the uranium moments is observed, forming complex non-collinear 3-k magnetic structure. This transition is accompanied by Jahn-Teller distortion of oxygen atoms. It is believed that the first order nature of the transition results from the competition between the exchange interaction and the Jahn-Teller distortion. Here we present results of our extensive thermodynamic investigations on well-characterized and oriented single crystals of UO 2+x (x = 0, 0.033, 0.04, and 0.11). By focusing on the transition region under applied magnetic field we are able to study the interplay between different competing interactions (structural, magnetic, and electrical), its dynamics, and relationship to the oxygen content. We will discuss implications of these results.

Bulletin of the American Physical Society, 2019

Inorganic Chemistry, 2014

Bulletin of the American Physical Society, 2018

Physical Review B, 2020

The perovskite TbFe0.5Cr0.5O3 shows two anomalies in the magnetic susceptibility at TN = 257 K an... more The perovskite TbFe0.5Cr0.5O3 shows two anomalies in the magnetic susceptibility at TN = 257 K and TSR = 190 K which are respectively, the antiferromagnetic and spin reorientation transition that occur in the Fe/Cr sublattice. Analysis of the magnetic susceptibility reveals signatures of Griffiths-like phase in this compound: the negative deviation from ideal Curie-Weiss law and in less-than-unity power-law susceptibility exponents. Neutron diffraction analysis confirms that, as the temperature is reduced from 350 K, a spin reorientation transition from Γ2 (Fx, Cy, Gz) to Γ4 (Gx, Ay, Fz) occurs at TN = 257 K and subsequently, a second spin reorientation takes place from Γ4 (Gx, Ay, Fz) to Γ2 (Fx, Cy, Gz) at TSR = 190 K. The Γ2 (Fx, Cy, Gz) structure is stable until 7.7 K where an ordered moment of 7.74(1)µB/Fe 3+ (Cr 3+) is obtained from neutron data refinement. In addition to the long-range order of the magnetic structure, indication of diffuse magnetic scattering at 7.7 K is evident, thereby lending support to the Griffiths-like phase observed in susceptibility. At 7.7 K, Tb develops a ferromagnetic component along the crystallographic a axis. Thermal conductivity, and spin-phonon coupling of TbFe0.5Cr0.5O3 through Raman spectroscopy are studied in the present work. The magnetic anomalies at TN and TSR do not reflect in the thermal conductivity data of TbFe0.5Cr0.5O3; however, it is noticeable that the application of 9 T magnetic field has no effect on the thermal conductivity. The TN and TSR are revealed in the temperature-dependence of full-width-at-half-maximum curves obtained from Raman intensities. An antiferromagnetic structure with (↑↓↑↓) arrangement of Fe/Cr spins is found in the ground state through first-principles energy calculations which supports the experimental magnetic structure at 7.7 K. The spin-resolved total and partial density of states are determined showing that TbFe0.5Cr0.5O3 is insulating with a band gap of ∼ 0.12 (2.4) eV within GGA (GGA+U) functionals

Journal of Alloys and Compounds, 2018

High temperature synthesis and optical band gaps are reported for three candidate photovoltaic ea... more High temperature synthesis and optical band gaps are reported for three candidate photovoltaic earth-abundant Cu 2 PbSiS 4 , Ag 2 PbGeS 4 and KAg 2 SbS 4 semiconductors. The reported synthesis method is found to be more advantageous for KAg 2 SbS 4 compared to the literature reported synthesis utilizing supercritical ammonia as a reaction medium, which produces a mixture of chalcogenide products. Based on optical diffuse reflectance data, Cu 2 PbSiS 4 , Ag 2 PbGeS 4 and KAg 2 SbS 4 have band gaps in the 1.6-1.8 eV range, and are shown to be stable in ambient air for a period of 6 weeks, making them attractive candidates for solar cell applications. Density functional theory (DFT) calculations indicate indirect band gaps for Cu 2 PbSiS 4 and KAg 2 SbS 4 , and a nearly direct band gap for Ag 2 PbGeS 4 with the calculated difference between indirect and direct gaps of only 30 meV. The p-type semiconducting behavior of Cu 2 PbSiS 4 , Ag 2 PbGeS 4 is also verified by the transport measurments. The 3D connectivity of the polyanionic networks in these compounds results in dispersive valence and conduction bands, which is especially noticeable for KAg 2 SbS 4. This fact is in part attributed to the presence of formally pentavalent Sb V in this compound leading to empty Sb 5s orbitals in the conduction band. We discuss the potential of Cu 2 PbSiS 4 , Ag 2 PbGeS 4 and KAg 2 SbS 4 for photovoltaic applications based on synthesis, stability, band gap and electronic structre considerations.

Journal of Nuclear Materials, 2018

We have studied U3Si2 by means of the heat capacity, electrical resistivity, Seebeck and Hall eff... more We have studied U3Si2 by means of the heat capacity, electrical resistivity, Seebeck and Hall effects, and thermal conductivity in the temperature range 2-300 K and in magnetic fields up to 9 T. All the results obtained point to delocalized nature of 5f-electrons in this material. The low temperature heat capacity is enhanced (gel ~ 150 mJ/mol-K 2) and shows an upturn in Cp/T (T), characteristic of spin fluctuations. The thermal conductivity of U3Si2 is ~8.5 W/m-K at room temperature and we show that the electronic part dominates heat transport above 300 K as expected for a metallic system, although the lattice contribution cannot be completely neglected.

Journal of physics. Condensed matter : an Institute of Physics journal, Jan 15, 2016

We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence y... more We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L3 edge (0-28.2 GPa) and single crystal x-ray diffraction (SXD) (0-20 GPa) on the UCd11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K 0 = 62(1) GPa and its pressure derivative, [Formula: see text] = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.

Inorganic Chemistry, 2015

The crystal structure and the Yb valence of the YbFe 2 Ge 2 heavy fermion compound was measured a... more The crystal structure and the Yb valence of the YbFe 2 Ge 2 heavy fermion compound was measured at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. The measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. While the ThCr 2 Si 2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) at ambient pressure to v = 2.93(3) at ∼9 GPa, where at low temperature a pressure-induced quantum critical state was reported.

Scientific Reports, 2015

Transition-metal (TM) nitrides are a class of compounds with a wide range of properties and appli... more Transition-metal (TM) nitrides are a class of compounds with a wide range of properties and applications. Hard superconducting nitrides are of particular interest for electronic applications under working conditions such as coating and high stress (e.g., electromechanical systems). However, most of the known TM nitrides crystallize in the rock-salt structure, a structure that is unfavorable to resist shear strain, and they exhibit relatively low indentation hardness, typically in the range of 10-20 GPa. Here, we report high-pressure synthesis of hexagonal δ-MoN and cubic γ-MoN through an ionexchange reaction at 3.5 GPa. The final products are in the bulk form with crystallite sizes of 50-80 μm. Based on indentation testing on single crystals, hexagonal δ-MoN exhibits excellent hardness of ~30 GPa, which is 30% higher than cubic γ-MoN (~23 GPa) and is so far the hardest among the known metal nitrides. The hardness enhancement in hexagonal phase is attributed to extended covalently bonded Mo-N network than that in cubic phase. The measured superconducting transition temperatures for δ-MoN and cubic γ-MoN are 13.8 and 5.5 K, respectively, in good agreement with previous measurements.

Intermetallic compounds show high hydrogen sorption capacities when pressurized with hydrogen. Fu... more Intermetallic compounds show high hydrogen sorption capacities when pressurized with hydrogen. Further, they are also used in hydride compressors [1]. The structure of intermetallic ZrFe2, which can contain about 1.7 wt/% hydrogen around 0.18 GPa, was studied using XRD at high pressures up to 47 GPa using a diamond anvil cell and synchrotron x-rays. The cubic Fd3m Laves phase is found to be stable and the bulk modulus was found to be 163.5 GPa which compares well with other intermetallics. The variation of unit structural parameters and the equation of state are discussed.

Materials Science Forum, 2014

High-pressure studies on strongly correlated-electron systems allow the study of the relationship... more High-pressure studies on strongly correlated-electron systems allow the study of the relationship between structural, elastic, electronic, and magnetic properties of d-and f-band systems. The High Pressure Science and Engineering Center (HiPSEC) at UNLV performs interdisciplinary research on a wide variety of materials at high pressures. One such system, YbB2 displays antiferromagnet order at ambient pressure. We present heat capacity measurements at high magnetic fields to 9 T and structural measurement at pressures up to 5 GPa on YbB2.

Physica B: Condensed Matter, 2015

The crystal structure of A-15 superconductor Nb 3 Ga with a critical temperature T c = 16.5 K has... more The crystal structure of A-15 superconductor Nb 3 Ga with a critical temperature T c = 16.5 K has been investigated by high pressure x-ray diffraction (HPXRD) using synchrotron x-rays and a diamond anvil cell under Ne pressure medium. The high pressure structural results indicate that Nb 3 Ga is stable up to 41 GPa. The P-V plot shows an anomaly around 15 GPa even though there are no pressure induced structural transitions are observed. High pressure resistance measurements were performed up to 0.5 GPa to understand the variation of T c under pressure. Our results show a positive pressure effect on T c .

Procedia Chemistry, 2012

Technetium-99 is one of the most abundant, long-lived radiotoxic isotopes in used nuclear fuel (U... more Technetium-99 is one of the most abundant, long-lived radiotoxic isotopes in used nuclear fuel (UNF). As such, it is targeted in UNF separation strategies such as UREX+, for isolation and encapsulation in solid waste forms for storage in a nuclear repository. We report here results regarding the incorporation of Tc-99 into ternary oxides of different structure types: pyrochlore (Nd 2 Tc 2 O 7), perovskite (SrTcO 3), and layered perovskite (Sr 2 TcO 4). The goal was to determine synthesis conditions of these potential waste forms to immobilize Tc-99 and to harvest crystallographic, thermophysical and hydrodynamic data. Within these studies, Rietveld structure refinement was applied to allow for crystallographic characterization, while a physical property measurement system (PPMS) was used to determine thermophysical properties. The ternary oxides exhibited good crystallinity and their lattice parameters and atomic coordinates could be refined to high accuracy. Low refinement residuals (R Bragg) of 2.0, 2.4, and 3.9 % were achieved for Nd 2 Tc 2 O 7 , SrTcO 3 , and Sr 2 TcO 4 , respectively. The strontium technetates, SrTcO 3 and Sr 2 TcO 4, show superconductivity at rather high critical temperatures of T c = 7.8 K and 7 K, respectively. Nd 2 Tc 2 O 7 did not show any changes in magnetic properties above 3 K.

Physics Letters B, 2011

A search for physics beyond the standard model in events with at least three leptons and any numb... more A search for physics beyond the standard model in events with at least three leptons and any number of jets is presented. The data sample corresponds to 35 pb −1 of integrated luminosity in pp collisions at √ s = 7 TeV collected by the CMS experiment at the LHC. A number of exclusive multileptonic channels are investigated and standard model backgrounds are suppressed by requiring sufficient missing transverse energy, invariant mass inconsistent with that of the Z boson, or high jet activity. Control samples in data are used to ascertain the robustness of background evaluation techniques and to minimise the reliance on simulation. The observations are consistent with background expectations. These results constrain previously unexplored regions of supersymmetric parameter space.

Physics Letters B, 2011

A search for narrow resonances with a mass of at least 1 TeV in the dijet mass spectrum is perfor... more A search for narrow resonances with a mass of at least 1 TeV in the dijet mass spectrum is performed using pp collisions at √ s = 7 TeV corresponding to an integrated luminosity of 1 fb −1 , collected by the CMS experiment at the LHC. No resonances are observed. Upper limits at the 95% confidence level are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, and gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% confidence level: string resonances with mass less than 4.00 TeV, E 6 diquarks with mass less than 3.52 TeV, excited quarks with mass less than 2.49 TeV, axigluons and colorons with mass less than 2.47 TeV, and W bosons with mass less than 1.51 TeV. These results extend previous exclusions from the dijet mass search technique.

Physical Review B, 2006

We have studied the spin relaxation in diluted spin ice Ho 2−x Y x Ti 2 O 7 by means of neutron s... more We have studied the spin relaxation in diluted spin ice Ho 2−x Y x Ti 2 O 7 by means of neutron spin echo spectroscopy and ac susceptibility measurements. Remarkably, the geometrical frustration is not relieved by doping with nonmagnetic Y, and the dynamics of the freezing is unaltered in the spin echo time window up to x Ӎ 1.6. At higher doping with nonmagnetic Y ͑x Ն 1.6͒ a new relaxation process at relatively high temperature ͑up to at least T Ӎ 55 K͒ appears which is more than 10 times faster than the thermally activated main relaxation process. We find evidence that over the whole range of composition all Ho spins participate in the dynamics. These results are compared to ac susceptibility measurements of the diluted Ho and Dy spin ice systems, which show that at low temperature the Arrhenius behavior is masked by another dynamical process with little temperature dependence. X-ray absorption fine structure ͑EXAFS͒ spectra and x-ray diffraction show that the samples are structurally well ordered.

Obesity Surgery, 2005

Background: Scopinaro biliopancreatic diversion (BPD) for morbid obesity results in significant l... more Background: Scopinaro biliopancreatic diversion (BPD) for morbid obesity results in significant longterm weight loss and reduction or resolution of obesity-associated co-morbidities. The aim of our work was to describe the early results after BPD. Methods: 59 morbidly obese patients (BMI >40) underwent open BPD from December 2001 to December 2004. We analyzed a consecutive series of 19 patients who have been followed >4 months. We present the data of basal and early visits (2 and 4 months). Results: Initial excess weight percent loss (IEW%L) was 5.2% at 2 months and 13.7% at 4 months. Glycemia, cholesterol, triglyceride levels and blood pressure improved at each visit. All parameters have significant differences from the basal values. 3 patients had sleep apnea syndrome, and overnight CPAP was able to cease in 2 patients by 4 months. 6 patients (31.5%) had albumin <2.5 g/dl, without clinical findings of malnutrition. Total calorie (857±79.8 cal/day) and protein (59.8±23 g/day) intakes at 4 months were low, with a low intake of multivitamins and oligoelements from food. There was no mortality in this series. Early postoperative morbidity was incisional hernia (21.1%), anastomotic leak (5.2%), wound infection (15.7%), intra-abdominal infection (5.2%), and intestinal obstruction (5.2%). Conclusion: BPD showed early effectiveness in weight loss and co-morbidity improvement. Calorie, protein, oligoelement and vitamin dietary intakes were below recommendations, so that strict multidisciplinary follow-up and supplementation to prevent or treat nutritional deficiencies are mandatory.

Lawrence Berkeley National Laboratory, Nov 18, 2004

We present neutron diffraction, magnetic susceptibility and specific heat data for a single-cryst... more We present neutron diffraction, magnetic susceptibility and specific heat data for a single-crystal sample of the cubic (Cu 3 Au structure) compound Pr 3 In. This compound is believed to have a singlet (Γ 1) groundstate and a low-lying triplet (Γ 4) excited state. In addition, nearest-neighbor antiferromagnetic interactions are frustrated in this structure. Antiferromagnetic order occurs below T N = 12K with propagation vector (0, 0, 0.5≤δ) where δ ≈ 1/12. The neutron diffraction results can be approximated with the following model: ferromagnetic sheets from each of the three Pr sites alternate in sign along the propagation direction with a twelve-unit-cell square-wave modulation. The three moments of the unit cell of 1 µ B magnitude are aligned so as to sum to zero as expected for nearest-neighbor antiferromagnetic interactions on a triangle. The magnetic susceptibility indicates that in addition to the antiferromagnetic transition at 12K, there is a transition near 70K below which there is a small (0.005 µ B) ferromagnetic moment. There is considerable field and sample dependence to these transitions. The specific heat data show almost no anomaly at T N = 12K. This may be a consequence of the induced moment in the Γ 1 singlet, but may also be a sample-dependent effect.

Bulletin of the American Physical Society, 2017

Submitted for the MAR17 Meeting of The American Physical Society On the nature of the phase trans... more Submitted for the MAR17 Meeting of The American Physical Society On the nature of the phase transition in uranium dioxide 1 K. GOFRYK, INL, D. MAST, INL, UNLV, D. ANTONIO, K. SHRESTHA, INL, D. ANDERSSON , C. STANEK, M. JAIME, LANL-Uranium dioxide (UO 2) is by far the most studied actinide material as it is a primary fuel used in light water nuclear reactors. Its thermal and magnetic properties remain, however, a puzzle resulting from strong couplings between magnetism and lattice vibrations. UO 2 crystalizes in the face-centered-cubic fluorite structure and is a Mott-Hubbard insulator with well-localized uranium 5f-electrons. In addition, below 30 K, a long range antiferromagnetic ordering of the electric-quadrupole of the uranium moments is observed, forming complex non-collinear 3-k magnetic structure. This transition is accompanied by Jahn-Teller distortion of oxygen atoms. It is believed that the first order nature of the transition results from the competition between the exchange interaction and the Jahn-Teller distortion. Here we present results of our extensive thermodynamic investigations on well-characterized and oriented single crystals of UO 2+x (x = 0, 0.033, 0.04, and 0.11). By focusing on the transition region under applied magnetic field we are able to study the interplay between different competing interactions (structural, magnetic, and electrical), its dynamics, and relationship to the oxygen content. We will discuss implications of these results.

Bulletin of the American Physical Society, 2019

Inorganic Chemistry, 2014

Bulletin of the American Physical Society, 2018

Physical Review B, 2020

The perovskite TbFe0.5Cr0.5O3 shows two anomalies in the magnetic susceptibility at TN = 257 K an... more The perovskite TbFe0.5Cr0.5O3 shows two anomalies in the magnetic susceptibility at TN = 257 K and TSR = 190 K which are respectively, the antiferromagnetic and spin reorientation transition that occur in the Fe/Cr sublattice. Analysis of the magnetic susceptibility reveals signatures of Griffiths-like phase in this compound: the negative deviation from ideal Curie-Weiss law and in less-than-unity power-law susceptibility exponents. Neutron diffraction analysis confirms that, as the temperature is reduced from 350 K, a spin reorientation transition from Γ2 (Fx, Cy, Gz) to Γ4 (Gx, Ay, Fz) occurs at TN = 257 K and subsequently, a second spin reorientation takes place from Γ4 (Gx, Ay, Fz) to Γ2 (Fx, Cy, Gz) at TSR = 190 K. The Γ2 (Fx, Cy, Gz) structure is stable until 7.7 K where an ordered moment of 7.74(1)µB/Fe 3+ (Cr 3+) is obtained from neutron data refinement. In addition to the long-range order of the magnetic structure, indication of diffuse magnetic scattering at 7.7 K is evident, thereby lending support to the Griffiths-like phase observed in susceptibility. At 7.7 K, Tb develops a ferromagnetic component along the crystallographic a axis. Thermal conductivity, and spin-phonon coupling of TbFe0.5Cr0.5O3 through Raman spectroscopy are studied in the present work. The magnetic anomalies at TN and TSR do not reflect in the thermal conductivity data of TbFe0.5Cr0.5O3; however, it is noticeable that the application of 9 T magnetic field has no effect on the thermal conductivity. The TN and TSR are revealed in the temperature-dependence of full-width-at-half-maximum curves obtained from Raman intensities. An antiferromagnetic structure with (↑↓↑↓) arrangement of Fe/Cr spins is found in the ground state through first-principles energy calculations which supports the experimental magnetic structure at 7.7 K. The spin-resolved total and partial density of states are determined showing that TbFe0.5Cr0.5O3 is insulating with a band gap of ∼ 0.12 (2.4) eV within GGA (GGA+U) functionals

Journal of Alloys and Compounds, 2018

High temperature synthesis and optical band gaps are reported for three candidate photovoltaic ea... more High temperature synthesis and optical band gaps are reported for three candidate photovoltaic earth-abundant Cu 2 PbSiS 4 , Ag 2 PbGeS 4 and KAg 2 SbS 4 semiconductors. The reported synthesis method is found to be more advantageous for KAg 2 SbS 4 compared to the literature reported synthesis utilizing supercritical ammonia as a reaction medium, which produces a mixture of chalcogenide products. Based on optical diffuse reflectance data, Cu 2 PbSiS 4 , Ag 2 PbGeS 4 and KAg 2 SbS 4 have band gaps in the 1.6-1.8 eV range, and are shown to be stable in ambient air for a period of 6 weeks, making them attractive candidates for solar cell applications. Density functional theory (DFT) calculations indicate indirect band gaps for Cu 2 PbSiS 4 and KAg 2 SbS 4 , and a nearly direct band gap for Ag 2 PbGeS 4 with the calculated difference between indirect and direct gaps of only 30 meV. The p-type semiconducting behavior of Cu 2 PbSiS 4 , Ag 2 PbGeS 4 is also verified by the transport measurments. The 3D connectivity of the polyanionic networks in these compounds results in dispersive valence and conduction bands, which is especially noticeable for KAg 2 SbS 4. This fact is in part attributed to the presence of formally pentavalent Sb V in this compound leading to empty Sb 5s orbitals in the conduction band. We discuss the potential of Cu 2 PbSiS 4 , Ag 2 PbGeS 4 and KAg 2 SbS 4 for photovoltaic applications based on synthesis, stability, band gap and electronic structre considerations.

Journal of Nuclear Materials, 2018

We have studied U3Si2 by means of the heat capacity, electrical resistivity, Seebeck and Hall eff... more We have studied U3Si2 by means of the heat capacity, electrical resistivity, Seebeck and Hall effects, and thermal conductivity in the temperature range 2-300 K and in magnetic fields up to 9 T. All the results obtained point to delocalized nature of 5f-electrons in this material. The low temperature heat capacity is enhanced (gel ~ 150 mJ/mol-K 2) and shows an upturn in Cp/T (T), characteristic of spin fluctuations. The thermal conductivity of U3Si2 is ~8.5 W/m-K at room temperature and we show that the electronic part dominates heat transport above 300 K as expected for a metallic system, although the lattice contribution cannot be completely neglected.

Journal of physics. Condensed matter : an Institute of Physics journal, Jan 15, 2016

We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence y... more We report a study of high pressure x-ray absorption (XAS) performed in the partial fluorescence yield mode (PFY) at the U L3 edge (0-28.2 GPa) and single crystal x-ray diffraction (SXD) (0-20 GPa) on the UCd11 heavy fermion compound at room temperature. Under compression, the PFY-XAS results show that the white line is shifted by +4.1(3) eV at the highest applied pressure of 28.2 GPa indicating delocalization of the 5f electrons. The increase in full width at half maxima and decrease in relative amplitude of the white line with respect to the edge jump point towards 6d band broadening under high pressure. A bulk modulus of K 0 = 62(1) GPa and its pressure derivative, [Formula: see text] = 4.9(2) was determined from high pressure SXD results. Both the PFY-XAS and diffraction results do not show any sign of a structural phase transition in the applied pressure range.

Inorganic Chemistry, 2015

The crystal structure and the Yb valence of the YbFe 2 Ge 2 heavy fermion compound was measured a... more The crystal structure and the Yb valence of the YbFe 2 Ge 2 heavy fermion compound was measured at room temperature and under high pressures using high-pressure powder X-ray diffraction and X-ray absorption spectroscopy via both partial fluorescence yield and resonant inelastic X-ray emission techniques. The measurements are complemented by first-principles density functional theoretical calculations using the self-interaction corrected local spin density approximation investigating in particular the magnetic structure and the Yb valence. While the ThCr 2 Si 2-type tetragonal (I4/mmm) structure is stable up to 53 GPa, the X-ray emission results show an increase of the Yb valence from v = 2.72(2) at ambient pressure to v = 2.93(3) at ∼9 GPa, where at low temperature a pressure-induced quantum critical state was reported.

Scientific Reports, 2015

Transition-metal (TM) nitrides are a class of compounds with a wide range of properties and appli... more Transition-metal (TM) nitrides are a class of compounds with a wide range of properties and applications. Hard superconducting nitrides are of particular interest for electronic applications under working conditions such as coating and high stress (e.g., electromechanical systems). However, most of the known TM nitrides crystallize in the rock-salt structure, a structure that is unfavorable to resist shear strain, and they exhibit relatively low indentation hardness, typically in the range of 10-20 GPa. Here, we report high-pressure synthesis of hexagonal δ-MoN and cubic γ-MoN through an ionexchange reaction at 3.5 GPa. The final products are in the bulk form with crystallite sizes of 50-80 μm. Based on indentation testing on single crystals, hexagonal δ-MoN exhibits excellent hardness of ~30 GPa, which is 30% higher than cubic γ-MoN (~23 GPa) and is so far the hardest among the known metal nitrides. The hardness enhancement in hexagonal phase is attributed to extended covalently bonded Mo-N network than that in cubic phase. The measured superconducting transition temperatures for δ-MoN and cubic γ-MoN are 13.8 and 5.5 K, respectively, in good agreement with previous measurements.

Intermetallic compounds show high hydrogen sorption capacities when pressurized with hydrogen. Fu... more Intermetallic compounds show high hydrogen sorption capacities when pressurized with hydrogen. Further, they are also used in hydride compressors [1]. The structure of intermetallic ZrFe2, which can contain about 1.7 wt/% hydrogen around 0.18 GPa, was studied using XRD at high pressures up to 47 GPa using a diamond anvil cell and synchrotron x-rays. The cubic Fd3m Laves phase is found to be stable and the bulk modulus was found to be 163.5 GPa which compares well with other intermetallics. The variation of unit structural parameters and the equation of state are discussed.

Materials Science Forum, 2014

High-pressure studies on strongly correlated-electron systems allow the study of the relationship... more High-pressure studies on strongly correlated-electron systems allow the study of the relationship between structural, elastic, electronic, and magnetic properties of d-and f-band systems. The High Pressure Science and Engineering Center (HiPSEC) at UNLV performs interdisciplinary research on a wide variety of materials at high pressures. One such system, YbB2 displays antiferromagnet order at ambient pressure. We present heat capacity measurements at high magnetic fields to 9 T and structural measurement at pressures up to 5 GPa on YbB2.

Physica B: Condensed Matter, 2015

The crystal structure of A-15 superconductor Nb 3 Ga with a critical temperature T c = 16.5 K has... more The crystal structure of A-15 superconductor Nb 3 Ga with a critical temperature T c = 16.5 K has been investigated by high pressure x-ray diffraction (HPXRD) using synchrotron x-rays and a diamond anvil cell under Ne pressure medium. The high pressure structural results indicate that Nb 3 Ga is stable up to 41 GPa. The P-V plot shows an anomaly around 15 GPa even though there are no pressure induced structural transitions are observed. High pressure resistance measurements were performed up to 0.5 GPa to understand the variation of T c under pressure. Our results show a positive pressure effect on T c .

Procedia Chemistry, 2012

Technetium-99 is one of the most abundant, long-lived radiotoxic isotopes in used nuclear fuel (U... more Technetium-99 is one of the most abundant, long-lived radiotoxic isotopes in used nuclear fuel (UNF). As such, it is targeted in UNF separation strategies such as UREX+, for isolation and encapsulation in solid waste forms for storage in a nuclear repository. We report here results regarding the incorporation of Tc-99 into ternary oxides of different structure types: pyrochlore (Nd 2 Tc 2 O 7), perovskite (SrTcO 3), and layered perovskite (Sr 2 TcO 4). The goal was to determine synthesis conditions of these potential waste forms to immobilize Tc-99 and to harvest crystallographic, thermophysical and hydrodynamic data. Within these studies, Rietveld structure refinement was applied to allow for crystallographic characterization, while a physical property measurement system (PPMS) was used to determine thermophysical properties. The ternary oxides exhibited good crystallinity and their lattice parameters and atomic coordinates could be refined to high accuracy. Low refinement residuals (R Bragg) of 2.0, 2.4, and 3.9 % were achieved for Nd 2 Tc 2 O 7 , SrTcO 3 , and Sr 2 TcO 4 , respectively. The strontium technetates, SrTcO 3 and Sr 2 TcO 4, show superconductivity at rather high critical temperatures of T c = 7.8 K and 7 K, respectively. Nd 2 Tc 2 O 7 did not show any changes in magnetic properties above 3 K.

Physics Letters B, 2011

A search for physics beyond the standard model in events with at least three leptons and any numb... more A search for physics beyond the standard model in events with at least three leptons and any number of jets is presented. The data sample corresponds to 35 pb −1 of integrated luminosity in pp collisions at √ s = 7 TeV collected by the CMS experiment at the LHC. A number of exclusive multileptonic channels are investigated and standard model backgrounds are suppressed by requiring sufficient missing transverse energy, invariant mass inconsistent with that of the Z boson, or high jet activity. Control samples in data are used to ascertain the robustness of background evaluation techniques and to minimise the reliance on simulation. The observations are consistent with background expectations. These results constrain previously unexplored regions of supersymmetric parameter space.

Physics Letters B, 2011

A search for narrow resonances with a mass of at least 1 TeV in the dijet mass spectrum is perfor... more A search for narrow resonances with a mass of at least 1 TeV in the dijet mass spectrum is performed using pp collisions at √ s = 7 TeV corresponding to an integrated luminosity of 1 fb −1 , collected by the CMS experiment at the LHC. No resonances are observed. Upper limits at the 95% confidence level are presented on the product of the resonance cross section, branching fraction into dijets, and acceptance, separately for decays into quark-quark, quark-gluon, and gluon-gluon pairs. The data exclude new particles predicted in the following models at the 95% confidence level: string resonances with mass less than 4.00 TeV, E 6 diquarks with mass less than 3.52 TeV, excited quarks with mass less than 2.49 TeV, axigluons and colorons with mass less than 2.47 TeV, and W bosons with mass less than 1.51 TeV. These results extend previous exclusions from the dijet mass search technique.

Physical Review B, 2006

We have studied the spin relaxation in diluted spin ice Ho 2−x Y x Ti 2 O 7 by means of neutron s... more We have studied the spin relaxation in diluted spin ice Ho 2−x Y x Ti 2 O 7 by means of neutron spin echo spectroscopy and ac susceptibility measurements. Remarkably, the geometrical frustration is not relieved by doping with nonmagnetic Y, and the dynamics of the freezing is unaltered in the spin echo time window up to x Ӎ 1.6. At higher doping with nonmagnetic Y ͑x Ն 1.6͒ a new relaxation process at relatively high temperature ͑up to at least T Ӎ 55 K͒ appears which is more than 10 times faster than the thermally activated main relaxation process. We find evidence that over the whole range of composition all Ho spins participate in the dynamics. These results are compared to ac susceptibility measurements of the diluted Ho and Dy spin ice systems, which show that at low temperature the Arrhenius behavior is masked by another dynamical process with little temperature dependence. X-ray absorption fine structure ͑EXAFS͒ spectra and x-ray diffraction show that the samples are structurally well ordered.

Obesity Surgery, 2005

Background: Scopinaro biliopancreatic diversion (BPD) for morbid obesity results in significant l... more Background: Scopinaro biliopancreatic diversion (BPD) for morbid obesity results in significant longterm weight loss and reduction or resolution of obesity-associated co-morbidities. The aim of our work was to describe the early results after BPD. Methods: 59 morbidly obese patients (BMI >40) underwent open BPD from December 2001 to December 2004. We analyzed a consecutive series of 19 patients who have been followed >4 months. We present the data of basal and early visits (2 and 4 months). Results: Initial excess weight percent loss (IEW%L) was 5.2% at 2 months and 13.7% at 4 months. Glycemia, cholesterol, triglyceride levels and blood pressure improved at each visit. All parameters have significant differences from the basal values. 3 patients had sleep apnea syndrome, and overnight CPAP was able to cease in 2 patients by 4 months. 6 patients (31.5%) had albumin <2.5 g/dl, without clinical findings of malnutrition. Total calorie (857±79.8 cal/day) and protein (59.8±23 g/day) intakes at 4 months were low, with a low intake of multivitamins and oligoelements from food. There was no mortality in this series. Early postoperative morbidity was incisional hernia (21.1%), anastomotic leak (5.2%), wound infection (15.7%), intra-abdominal infection (5.2%), and intestinal obstruction (5.2%). Conclusion: BPD showed early effectiveness in weight loss and co-morbidity improvement. Calorie, protein, oligoelement and vitamin dietary intakes were below recommendations, so that strict multidisciplinary follow-up and supplementation to prevent or treat nutritional deficiencies are mandatory.