High-pressure behaviour of synthetic weberite-type Mn 2+ 2 Sb 5+ 2 O 7: An in situ single-crystal X-ray study (original) (raw)
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High-pressure behavior of the synthetic Ca2Sb2O7 weberite-type compound
Solid State Sciences, 2011
An in situ high-pressure X-ray diffraction study has been carried out at room temperature up to 9.23 GPa on a crystal of Ca 2 Sb 2 O 7 having a weberite-2O structure synthesized by solid-state reaction. A 2nd-order BircheMurnaghan Equation of State (EoS) was used to refine the pressureevolume data. The refinement of the unit-cell volume and of the isothermal bulk modulus at room pressure leads to: V 0 ¼ 555.8 (1), K T0 ¼ 154.6 (9) GPa. Unit-cell parameters decrease gradually as a function of pressure with a bulk modulus anisotropy scheme K a0 > K b0 > K c0 , with c being the softest direction. The compressional behavior of Ca 2 Sb 2 O 7 is compared with that shown by ingersonite, Ca 3 MnSb 4 O 14 , a mineral showing a weberite-3T structure.
Structural control of polyhedral compression in synthetic braunite, Mn 2+ Mn 3+ 6 O 8 SiO 4
Physics and Chemistry of Minerals, 1998
The compression of synthetic braunite, Mn 2+ Mn 3+ 6 O 8 SiO 4 , was studied by high-pressure singlecrystal X-ray diffraction carried out in a diamond-anvil cell. The equation of state at room temperature (third-order Birch-Murnaghan equation of state: V 0 =1661.15(8) 3 , K 0,298 =180.70.9 GPa, K©=6.50.3) was determined from unit-cell volume data to 9.18 GPa. Crystal structures were determined at 6 different pressures to 7.69 GPa. Compression of the structure (space group I4 1 /acd) was found to be slightly anisotropic (a 0 =9.4262(4) , K a =4994 GPa, K a ©=19.70.9; c 0 =18.6964(6) , K c =6576 GPa, K c ©=15.71.4) which can be attributed to the fact that the Mn 3+-O bonds, which are the most compressible bonds, are aligned closer to the (001) plane than to the c axis. The large bulk modulus is the result of the structural topology in which 2/3 and 1/2 of the edges of the Mn 2+ O 8 and Mn 3+ O 6 polyhedra share edges with other polyhedra. The Mn 2+ O 8 polyhedra were found to compress isotropically, whereas anisotropic compressional behaviour was observed for all three Mn 3+ O 6 octahedra. Although the polyhedral geometry of all three crystallographically independent Mn 3+ sites shows the same type of uniaxially elongated distortion, the compression of the individual octahedral configurations was found to be strongly dependent upon both the geometry of the polyhedron itself and the types of, and the connectivity to, the neighbouring polyhedra. The differences in the configuration of the different oxygen atoms, and therefore the structural topology, is one of the major factors determining the type and degree of the pressure-induced distortion, while the Jahn-Teller effect plays a subordinate role.
Physics and Chemistry of Minerals, 1998
Single crystals of the garnet Mn 2+ 3 Mn 3+ 2 [SiO 4 ] 3 and coesite were synthesised from MnO 2-SiO 2 oxide mixtures at 1000C and 9 GPa in a multianvil press. The crystal structure of the garnet [space group Ia3 Å d, a=11.801(2) ] was refined at room temperature and 100 K from single-crystal X-ray data to R1=2.36% and R1=2.71%, respectively. In contrast to tetragonal Ca 3 Mn 3+ 2 [GeO 4 ] 3 (space group I4 1 /a), the high-pressure garnet is cubic and does not display an ordered Jahn-Teller distortion of octahedral Mn 3+. A disordered Jahn-Teller distortion either dynamic or static is evidenced by unusual high anisotropic displacement parameters. The room temperature structure is characterised by following bond lengths: Si-O=1.636(4) (tetrahedron), Mn 3+-O=1.995 (4) (octahedron), Mn 2+-O=2.280(5) and 2.409(4) (dodecahedron). The cubic structure was preserved upon cooling to 100 K [a=11.788(2) ] and upon compressing up to 11.8 GPa in a diamond-anvil cell. Pressure variation of the unit cell parameter expressed by a third-order Birch-Murnaghan equation of state led to a bulk modulus K 0 =151.6(8) GPa and its pressure derivatives K©=6.38(19). The peak positions of the Raman spectrum recorded for Mn 2+ 3 Mn 3+ 2 [SiO 4 ] 3 were assigned based on a calderite Mn 2+ 3 Fe 3+ 2 [SiO 4 ] 3 model extrapolated from andradite and grossular literature data.
Physics and Chemistry of Minerals, 1998
Single crystals of the garnet Mn 2+ 3 Mn 3+ 2 [SiO 4 ] 3 and coesite were synthesised from MnO 2-SiO 2 oxide mixtures at 1000C and 9 GPa in a multianvil press. The crystal structure of the garnet [space group Ia3 Å d, a=11.801(2) ] was refined at room temperature and 100 K from single-crystal X-ray data to R1=2.36% and R1=2.71%, respectively. In contrast to tetragonal Ca 3 Mn 3+ 2 [GeO 4 ] 3 (space group I4 1 /a), the high-pressure garnet is cubic and does not display an ordered Jahn-Teller distortion of octahedral Mn 3+. A disordered Jahn-Teller distortion either dynamic or static is evidenced by unusual high anisotropic displacement parameters. The room temperature structure is characterised by following bond lengths: Si-O=1.636(4) (tetrahedron), Mn 3+-O=1.995 (4) (octahedron), Mn 2+-O=2.280(5) and 2.409(4) (dodecahedron). The cubic structure was preserved upon cooling to 100 K [a=11.788(2) ] and upon compressing up to 11.8 GPa in a diamond-anvil cell. Pressure variation of the unit cell parameter expressed by a third-order Birch-Murnaghan equation of state led to a bulk modulus K 0 =151.6(8) GPa and its pressure derivatives K©=6.38(19). The peak positions of the Raman spectrum recorded for Mn 2+ 3 Mn 3+ 2 [SiO 4 ] 3 were assigned based on a calderite Mn 2+ 3 Fe 3+ 2 [SiO 4 ] 3 model extrapolated from andradite and grossular literature data.
X-ray diffraction study of magnesite at high pressure and high temperature
Physics and Chemistry of Minerals, 1997
P -V -T measurements on magnesite MgCO 3 have been carried out at high pressure and high temperature up to 8.6 GPa and 1285 K, using a DIA-type, cubicanvil apparatus in conjunction with in situ synchrotron X-ray powder diffraction. Precise volumes are obtained by the use of data collected above 873 K on heating and in the entire cooling cycle to minimize nonhydrostatic stress. From these data, the equation-of-state parameters are derived from various approaches based on the Birch-Murnaghan equation of state and on the relevant thermodynamic relations. With KЈ 0 fixed at 4,
Physics and Chemistry of Minerals, 1997
The structural changes associated with the incommensurate (IC)-normal (N) phase transition in akermanite have been studied with high-pressure single-crystal X-ray diffraction up to 3.79 GPa. The IC phase, stable at room pressure, transforms to the N phase at ¥1.33 GPa. The structural transformation is marked by a small but discernable change in the slopes of all unitcell parameters as a function of pressure. It is reversible with an apparent hysteresis and is classified as a tricritical phase transition. The linear compressibility of the a and c axes are 0.00280 (10) and 0.00418 (6) GPa Ϫ1 for the IC phase, and 0.00299 (11) and 0.00367 (8) GPa Ϫ1 for the N phase, respectively. Weighted volume and pressure data, fitted to a second-order Birch-Murnaghan equation of state (KЈϵ4.0), yield V 0 ϭ307.4 (1) Å 3 and K 0 ϭ100 (3) GPa for the IC phase and V 0 ϭ307.6 (2) Å 3 and K 0 ϭ90 (2) GPa for the N phase. No significant discontinuities in Si-O, Mg-O and Ca-O distances were observed across the transition, except for the Ca-O 1 distance, which is more compressible in the IC phase than in the N phase. From room pressure to 3.79 GP the volume of the [SiO 4 ] tetrahedron is unchanged (2.16 Å 3), whereas the volumes of the [MgO 4 ] and [CaO 8 ] polyhedra decrease from 3.61 to 3.55 (1) Å 3 and 32.8 to 30.9 (2) Å 3 , respectively. Intensities of satellite reflections are found to vary linearly with the isotropic displacement parametr of Ca and the librational amplitude of the [SiO 4 ] tetrahedron. At room pressure, there is a mismatch between the size of the Ca cations and the configuration of tetrahedral sheets, which appears to be responsible for the formation of the modulated structure; as pressure increases, the misfit is diminished through the relative rotation and distortion of [MgO 4 ] and [SiO 4 ] tetrahedra and the differential compression of individual Ca-O distances, concurrent with a displacement of Ca along the (110) mirror plane toward the O 1 atom. We regard the high-pressure normal structure as a result of the elimination of microdomains in the modulated structure.
High-pressure study of the behaviour of mineral barite by X-ray diffraction
2015
In this paper, we report angle-dispersive X-ray diffraction data of barite, BaSO4, measured in a diamond-anvil cell up to a pressure of 48 GPa using three different fluid pressure-transmitting media (methanol-ethanol mixture, silicone oil, and He). Our results show that BaSO4 exhibits a phase transition at pressures that range from 15 to 27 GPa, depending on the pressure media used. This indicates that non-hydrostatic stresses have a crucial role in the high-pressure behaviour of this compound. The new highpressure phase has been solved and refined from powder data, having an orthorhombic P212121 structure. The pressure dependence of the structural parameters of both, roomand high-pressure phases of BaSO4 is also discussed in the light of our theoretical firstprinciples total-energy calculations. Finally, a comparison between the different equations of state obtained in our experiments is reported. * Corresponding author: dsantamaria@quim.ucm.es † MALTA Consolider Team PACS Numbers:...
2011
High-temperature study of the synthetic melilite-related Ba 2 MgSi 2 O 7 (s.g. C2/c) was performed up to 1273 K. Linear thermal expansion coefficients along the unit cell edges and of the volume are α a = 8.7×10 -6 K -1 , α b = 11.0×10 -6 K -1 , α c = 8.5×10 -6 K -1 , and α V = 31.1×10 -6 K -1 , respectively, showing an anisotropic expansion behaviour characterized by α a ≈ α c < α b . High-temperature data were then combined with high-pressure data (taken from the literature) for the same monoclinic sample. The "inverse relationship" of variation against temperature and pressure is observed for both the unit cell parameters and the (c/a) axial ratio as a function of the molar volume. A further comparison with melilite-type compounds at ambient condition along the join (Ca-Sr-Ba) 2 MgSi 2 O 7 reveals that the tetragonal polymorph of the barium compound (Ba 2 MgSi 2 O 7 ) should be a metastable phase favoured by high pressure conditions.
Journal of the American Ceramic Society, 2017
The compressional behaviour and the P-induced deformation mechanisms at the atomic scale of (Cs,K)Al4Be5B11O28 (londonite, a~7.31 Å and space group P 4 3m) were investigated by in-situ single-crystal synchrotron X-ray diffraction with a diamond anvil cell up to 26 GPa. No phase transition was observed within the P-range investigated: this material remains elastically isotropic (i.e., with cubic symmetry) in response to the applied pressure. Fitting the P-V data with a Birch-Murnaghan isothermal equation of state, we obtained: V0 = 390.8(3) Å 3 , KP0= 212(7) GPa (β0 = 1/KP0 = 0.0047(1) GPa-1) and K'= 4.6(6). A series of structural refinements, based on the high-pressure intensity data, were performed. The stiffness of londonite (similar to that of carbides) is governed by its close-packing structure, and in particular by the very low compressibility of Band Be-tetrahedra and the modest compressibility of the Al-octahedra. The Cs-polyhedra are the most compressible units of the structure. The effects of pressure can be accommodated by intra-polyhedral compression or deformation, leading to a modest bulk compression. The high amount of boron in londonite (B2O3~50wt%) makes its synthetic counterpart a potential neutron absorber. In addition, the high content of Cs makes londonite-type materials as potential hosts for nuclear waste.
Physics and Chemistry of Minerals, 2001
The structural behavior of synthetic gahnite (ZnAl 2 O 4) has been investigated by X-ray powder diffraction at high pressure (0±43 GPa) and room temperature, on the ID9 beamline at ESRF. The equation of state of gahnite has been derived using the models of Birch±Murnaghan, Vinet and Poirier±Tarantola, and the results have been mutually compared (the elastic bulk modulus and its derivatives versus P determined by the third-order Birch±Murnaghan equation of state are K 0 201.7(0.9) GPa, K H 0 7.62(0.09) and K HH 0)0.1022 GPa)1 (implied value). The compressibilities of the tetrahedral and octahedral bond lengths [0.00188(8) and 0.00142(5) GPa)1 at P 0, respectively], and the polyhedral volume compressibilities of the four-and sixfold coordination sites [0.0057(2) and 0.0041(2) GPa)1 at P 0, respectively] are discussed.