Ravhi Kumar - Academia.edu (original) (raw)
Papers by Ravhi Kumar
Physical Review Materials
Pressure is a unique tuning parameter for probing the properties of materials, and it has been pa... more Pressure is a unique tuning parameter for probing the properties of materials, and it has been particularly useful for studies of electronic materials such as high-temperature cuprate superconductors. Here we report the effects of quasihydrostatic compression produced by a neon pressure medium on the structures of bismuth-based high-T c cuprate superconductors with the nominal composition Bi 2 Sr 2 Ca n−1 Cu n O 2n+4+δ (n = 1, 2, 3) up to 155 GPa. The structures of all three compositions obtained by synchrotron x-ray diffraction can be described as pseudotetragonal over the entire pressure range studied. We show that previously reported pressure-induced distortions and structural changes arise from the large strains that can be induced in these layered materials by nonhydrostatic stresses. The pressure-volume equations of state (EOS) measured under these quasihydrostatic conditions cannot be fit to single phenomenological formulation over the pressure ranges studied, starting below 20 GPa. This intrinsic anomalous compression as well as the sensitivity of Bi 2 Sr 2 Ca n−1 Cu n O 2n+4+δ to deviatoric stresses provide explanations for the numerous inconsistencies in reported EOS parameters for these materials. We conclude that the anomalous compressional behavior of all three compositions is a manifestation of the changes in electronic properties that are also responsible for the remarkable nonmonotonic dependence of T c with pressure, including the increase in T c at the highest pressures studied so far for each. Transport and spectroscopic measurements up to megabar pressures are needed to fully characterize these cuprates and explore higher possible critical temperatures in these materials.
arXiv (Cornell University), Dec 13, 2022
The pressure transmitting medium is an important element in high pressure physics. A variety of p... more The pressure transmitting medium is an important element in high pressure physics. A variety of pressure transmitting media exist including Silicone fluid, Daphne Oil, 4:1 Methanol:Ethanol mixture, etc. In this experiment, the hydrostatic limits of pressure transmitting media have been observed at low temperatures and high pressures. In this case, 4:1 Methanol: Ethanol has been used. The hydrostaticity of 4:1 Methanol:Ethanol has been well studied at room temperatures using the fluorescence of ruby by fitting the R1 and R2 lines to Pseudo-Voigt functions. The hydrostacity of the pressure medium was determined by analyzing the full width at half max (FWHM) of
www.PosterPresentations.com In recent years, Quantum Dot (QD) materials have attracted considerab... more www.PosterPresentations.com In recent years, Quantum Dot (QD) materials have attracted considerable interest due to their versatile properties and potential applications in electronics, biology, and optoelectronics, i.e. photovoltaic solar cell materials [1-2]. In 2000, RincÓn et al. reported an extensive study of the bulk material of CuInTe2 along with its comparison to its ordered defect compounds [3]. The chalcopyrite structure consists of eight atoms per unit cell. This means there are 24 vibrational modes expected for the tetragonal structure. Out of the 24 modes, 21 vibrational modes belong to optical modes, and the other 3 modes are acoustical modes. The irreducible representation of the optical modes at Γ point is given as, Γ = 1A1 + 2A2 + 3B1 + 3B2 + 6E, where E modes are twofold degenerate vibrations. Theoretically, other than A2 modes, the optical modes at Γ point should be Raman-active [3]. At ambient conditions, both bulk and nanoparticle of CuInTe2 exhibit chalcopyrite...
Inorganic Chemistry, 2015
AIP Conference Proceedings, 2008
Recently, pressure tuning of the thermoelectric figure of merit has been reported for several mat... more Recently, pressure tuning of the thermoelectric figure of merit has been reported for several materials Bi2Te3 based thermoelectric materials [2],[10],[12]. In order to investigate the bulk properties of Bi2Te3, Sb2Te3, and their solid solution in detail, we have performed structural studies up to 20 GPa. Our diffraction results show that all three compounds transform from the ambient pressure structure to a high pressure phase between 7 and 10 GPa. In addition, these diffraction results have been converted to Vinet and Holzapfel equations of state to test the claim of electronic topological transitions in these structures [3].
AIP Conference Proceedings, 1999
High pressure X ray diffraction studies up to 15GPa were performed on the Y doped Bi2212 compound... more High pressure X ray diffraction studies up to 15GPa were performed on the Y doped Bi2212 compound with the rare earth concentration x=0.1 at the calcium site. From the studies it has been found that the system remains in the orthorhombic structure up to 15GPa. The relative volume is found to decrease around 15GPa. This may be a positive indication for a pressure induced structural transition in the system beyond 15GPa.
Bulletin of the American Physical Society, 2007
Recently Bi$_{2}$Te$_{3}$ based thermoelectric materials have gained importance due to their high... more Recently Bi$_{2}$Te$_{3}$ based thermoelectric materials have gained importance due to their high thermoelectric figure of merit in thin films [3]. Pressure tuning of the thermoelectric figure of merit has been reported for several materials [1],[2]. In order to investigate the bulk ...
Bulletin of the American Physical Society, 2010
III-V compounds of In and Ga are promising materials for optoelectronic, thermoelectric and nucle... more III-V compounds of In and Ga are promising materials for optoelectronic, thermoelectric and nuclear power engineering applications. Pressure induced structural changes have been reported previously for InTe, In$_{2}$Te$_{3}$, GaTe, and Ga$_ {2}$Te$_{3}$ at ambient temperature at ...
Bulletin of the American Physical Society, 2007
One of the current goals of the US Department of Energy is to find a new energy source that is no... more One of the current goals of the US Department of Energy is to find a new energy source that is non-reliant on fossil fuels for the production of energy. In an effort to address this concern, we have developed facilities to investigate the fundamental properties of thermoelectric ...
We have investigated the pressure-induced B1-to-B2 phase transitions in AgSbSe2. High pressure x-... more We have investigated the pressure-induced B1-to-B2 phase transitions in AgSbSe2. High pressure x-ray diffraction experiments clearly show that the process starts at 20 GPa and completes at 55 GPa. Our density-functional calculations are in good agreement with the experiment and confirm the B1 to B2 transition which is similar to AgSbTe2. The possible intermediate structure for B1-to-B2 transition in AgSbSe2 occurring at 21-54 GPa is under investigation. Its similarity and difference to AgSbTe2 will be discussed in this study.
The Journal of Physical Chemistry B, 2007
Review of Scientific Instruments, 2004
The properties of a silicone fluid with initial viscosity of 1 cst as a pressure transmitting med... more The properties of a silicone fluid with initial viscosity of 1 cst as a pressure transmitting medium for diamond anvil cells have been determined by ruby R1 line broadening and R1-R2 separation measurements to 64 GPa at ambient temperature. By these criteria, the silicone fluid is as good a pressure medium as a 4:1 methanol:ethanol mixture at low pressures to about 20 GPa, and is better than the mixture at higher pressures. Although argon media are better than the silicone at pressures to 30 GPa, this silicone behaves as well as argon at higher pressures. Furthermore, the silicone is easier to load than argon and is almost chemically inert.
Physical Review Materials
Pressure is a unique tuning parameter for probing the properties of materials, and it has been pa... more Pressure is a unique tuning parameter for probing the properties of materials, and it has been particularly useful for studies of electronic materials such as high-temperature cuprate superconductors. Here we report the effects of quasihydrostatic compression produced by a neon pressure medium on the structures of bismuth-based high-T c cuprate superconductors with the nominal composition Bi 2 Sr 2 Ca n−1 Cu n O 2n+4+δ (n = 1, 2, 3) up to 155 GPa. The structures of all three compositions obtained by synchrotron x-ray diffraction can be described as pseudotetragonal over the entire pressure range studied. We show that previously reported pressure-induced distortions and structural changes arise from the large strains that can be induced in these layered materials by nonhydrostatic stresses. The pressure-volume equations of state (EOS) measured under these quasihydrostatic conditions cannot be fit to single phenomenological formulation over the pressure ranges studied, starting below 20 GPa. This intrinsic anomalous compression as well as the sensitivity of Bi 2 Sr 2 Ca n−1 Cu n O 2n+4+δ to deviatoric stresses provide explanations for the numerous inconsistencies in reported EOS parameters for these materials. We conclude that the anomalous compressional behavior of all three compositions is a manifestation of the changes in electronic properties that are also responsible for the remarkable nonmonotonic dependence of T c with pressure, including the increase in T c at the highest pressures studied so far for each. Transport and spectroscopic measurements up to megabar pressures are needed to fully characterize these cuprates and explore higher possible critical temperatures in these materials.
arXiv (Cornell University), Dec 13, 2022
The pressure transmitting medium is an important element in high pressure physics. A variety of p... more The pressure transmitting medium is an important element in high pressure physics. A variety of pressure transmitting media exist including Silicone fluid, Daphne Oil, 4:1 Methanol:Ethanol mixture, etc. In this experiment, the hydrostatic limits of pressure transmitting media have been observed at low temperatures and high pressures. In this case, 4:1 Methanol: Ethanol has been used. The hydrostaticity of 4:1 Methanol:Ethanol has been well studied at room temperatures using the fluorescence of ruby by fitting the R1 and R2 lines to Pseudo-Voigt functions. The hydrostacity of the pressure medium was determined by analyzing the full width at half max (FWHM) of
www.PosterPresentations.com In recent years, Quantum Dot (QD) materials have attracted considerab... more www.PosterPresentations.com In recent years, Quantum Dot (QD) materials have attracted considerable interest due to their versatile properties and potential applications in electronics, biology, and optoelectronics, i.e. photovoltaic solar cell materials [1-2]. In 2000, RincÓn et al. reported an extensive study of the bulk material of CuInTe2 along with its comparison to its ordered defect compounds [3]. The chalcopyrite structure consists of eight atoms per unit cell. This means there are 24 vibrational modes expected for the tetragonal structure. Out of the 24 modes, 21 vibrational modes belong to optical modes, and the other 3 modes are acoustical modes. The irreducible representation of the optical modes at Γ point is given as, Γ = 1A1 + 2A2 + 3B1 + 3B2 + 6E, where E modes are twofold degenerate vibrations. Theoretically, other than A2 modes, the optical modes at Γ point should be Raman-active [3]. At ambient conditions, both bulk and nanoparticle of CuInTe2 exhibit chalcopyrite...
Inorganic Chemistry, 2015
AIP Conference Proceedings, 2008
Recently, pressure tuning of the thermoelectric figure of merit has been reported for several mat... more Recently, pressure tuning of the thermoelectric figure of merit has been reported for several materials Bi2Te3 based thermoelectric materials [2],[10],[12]. In order to investigate the bulk properties of Bi2Te3, Sb2Te3, and their solid solution in detail, we have performed structural studies up to 20 GPa. Our diffraction results show that all three compounds transform from the ambient pressure structure to a high pressure phase between 7 and 10 GPa. In addition, these diffraction results have been converted to Vinet and Holzapfel equations of state to test the claim of electronic topological transitions in these structures [3].
AIP Conference Proceedings, 1999
High pressure X ray diffraction studies up to 15GPa were performed on the Y doped Bi2212 compound... more High pressure X ray diffraction studies up to 15GPa were performed on the Y doped Bi2212 compound with the rare earth concentration x=0.1 at the calcium site. From the studies it has been found that the system remains in the orthorhombic structure up to 15GPa. The relative volume is found to decrease around 15GPa. This may be a positive indication for a pressure induced structural transition in the system beyond 15GPa.
Bulletin of the American Physical Society, 2007
Recently Bi$_{2}$Te$_{3}$ based thermoelectric materials have gained importance due to their high... more Recently Bi$_{2}$Te$_{3}$ based thermoelectric materials have gained importance due to their high thermoelectric figure of merit in thin films [3]. Pressure tuning of the thermoelectric figure of merit has been reported for several materials [1],[2]. In order to investigate the bulk ...
Bulletin of the American Physical Society, 2010
III-V compounds of In and Ga are promising materials for optoelectronic, thermoelectric and nucle... more III-V compounds of In and Ga are promising materials for optoelectronic, thermoelectric and nuclear power engineering applications. Pressure induced structural changes have been reported previously for InTe, In$_{2}$Te$_{3}$, GaTe, and Ga$_ {2}$Te$_{3}$ at ambient temperature at ...
Bulletin of the American Physical Society, 2007
One of the current goals of the US Department of Energy is to find a new energy source that is no... more One of the current goals of the US Department of Energy is to find a new energy source that is non-reliant on fossil fuels for the production of energy. In an effort to address this concern, we have developed facilities to investigate the fundamental properties of thermoelectric ...
We have investigated the pressure-induced B1-to-B2 phase transitions in AgSbSe2. High pressure x-... more We have investigated the pressure-induced B1-to-B2 phase transitions in AgSbSe2. High pressure x-ray diffraction experiments clearly show that the process starts at 20 GPa and completes at 55 GPa. Our density-functional calculations are in good agreement with the experiment and confirm the B1 to B2 transition which is similar to AgSbTe2. The possible intermediate structure for B1-to-B2 transition in AgSbSe2 occurring at 21-54 GPa is under investigation. Its similarity and difference to AgSbTe2 will be discussed in this study.
The Journal of Physical Chemistry B, 2007
Review of Scientific Instruments, 2004
The properties of a silicone fluid with initial viscosity of 1 cst as a pressure transmitting med... more The properties of a silicone fluid with initial viscosity of 1 cst as a pressure transmitting medium for diamond anvil cells have been determined by ruby R1 line broadening and R1-R2 separation measurements to 64 GPa at ambient temperature. By these criteria, the silicone fluid is as good a pressure medium as a 4:1 methanol:ethanol mixture at low pressures to about 20 GPa, and is better than the mixture at higher pressures. Although argon media are better than the silicone at pressures to 30 GPa, this silicone behaves as well as argon at higher pressures. Furthermore, the silicone is easier to load than argon and is almost chemically inert.