Characterization of the pressure-induced second-order phase transition in the mixed-valence vanadate BaV6O11

2009 ◽  
Vol 65 (3) ◽  
pp. 326-333 ◽  
Author(s):  
Karen Friese ◽  
Yasushi Kanke ◽  
Andrzej Grzechnik
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Ambient Pressure ◽  
Mixed Valence ◽  
Volume Effect ◽  
Unit Cell ◽  
Additional Degree ◽  
Diamond Anvil

The pressure dependence of the structure of the mixed-valence vanadate BaV6O11 was studied with single-crystal X-ray diffraction in a diamond–anvil cell. The compressibility data could be fitted with a Murnaghan equation of state with the zero-pressure bulk modulus B 0 = 161 (7) GPa and the unit-cell volume at ambient pressure = 387.1 (3) Å^3 (B′ = 4.00). A phase transition involving a symmetry reduction from P63/mmc to P63 mc can be reliably detected in the high-pressure data. The estimated transition pressure lies in the range 1.18 < P c < 3.09 GPa. The transition leads to a breaking of the regular Kagomé net formed by part of the V ions. While in the ambient pressure structure all V—V distances in the Kagomé net are equal, they split into inter-trimer and intra-trimer distances in the high-pressure phase. In general, these changes are comparable to those observed in the corresponding low-temperature transition. However, the pressure-induced transition takes place at a lower unit-cell volume compared with the temperature-induced transition. Furthermore, overall trends for inter-trimer and intra-trimer V—V distances as a function of the unit-cell volume are clearly different for datapoints obtained by variation of pressure and temperature. The behavior of BaV6O11 is compared with that of NaV6O11. While in the latter compound the transition can be explained as a pure volume effect, in BaV6O11 an additional degree of freedom related to the valence distribution among the symmetrically independent vanadium sites has to be taken into account.

scholarly journals Low-temperature phase transition and highpressure phase stability of 1H-pyrazole-1carboxamidine nitrate

2021 ◽  
Vol 77 (6) ◽  
Author(s):  
Piotr Rejnhardt ◽  
Marek Drozd ◽  
Marek Daszkiewicz
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Phase I ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Negative Thermal Expansion ◽  
Unit Cell ◽  
Monoclinic Space Group ◽  
Temperature Phase ◽  
Scanning Calorimetry

The phase transition observed in a temperature-dependent experiment at 174 K is unachievable under high-pressure conditions. Negative thermal expansion for phase (II) and negative compressibility for phase (I) were observed. A new salt of 1H-pyrazole-1-carboxamidine, (HPyCA)NO3, for guanylation reaction was obtained in a crystalline form. The compound crystallizes in monoclinic space group P21/c and a phase transition at 174 K to triclinic modification P 1 was found. An unusual increase of the unit-cell volume was observed just after transition. Although the volume decreases upon cooling, it remains higher down to 160 K in comparison to the unit-cell volume of phase (I). The mechanism of the phase transition is connected with a minor movement of the nitrate anions. The triclinic phase was unreachable at room-temperature high-pressure conditions up to 1.27 GPa. On further compression, delamination of the crystal was observed. Phase (I) exhibits negative linear compressibility, whereas abnormal behaviour of the b unit-cell parameter upon cooling was observed, indicating negative thermal linear expansion. The unusual nature of the compound is associated with the two-dimensional hydrogen-bonding network, which is less susceptible to deformation than stacking interactions connecting the layers of hydrogen bonds. Infrared spectroscopy and differential scanning calorimetry measurements were used to investigate the changes of intermolecular interactions during the phase transition.

FexCu1-xBa2YCu2O7+y SUPERCONDUCTORS SYNTHESIZED BY HIGH PRESSURE

2005 ◽  
Vol 19 (01n03) ◽  
pp. 221-223 ◽  
Author(s):  
Y. H. LIU ◽  
G. C. CHE ◽  
K. Q. LI ◽  
Z. X. ZHAO ◽  
Z. Q. KOU ◽  
...  
Keyword(s):  
High Pressure ◽  
Cell Volume ◽  
Oxygen Content ◽  
Unit Cell Volume ◽  
Ambient Pressure ◽  
Lattice Parameter ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
X Ray ◽  
Oxygen Coordination

Systematic studies of x-ray diffraction(XRD), superconductivity and Mössbauer effect on Fe x Cu 1-x Ba 2 YCu 2 O 7+y ( x =0.00~0.70) superconductors synthesized by high pressure (HP) were summarized. All the HP-samples have tetragonal structure, smaller lattice parameter c and unit-cell volume than the AM-samples (synthesized by ambient pressure). The HP-samples have higher oxygen content than the AM-samples. Moreover, for the HP-sample with x =0.5, all of the Fe located in the CuO x chains have fivefold-oxygen coordination.

High-pressure transformations of NbO2F

2000 ◽  
Vol 56 (2) ◽  
pp. 189-196 ◽  
Author(s):  
Stefan Carlson ◽  
Ann-Kristin Larsson ◽  
Franziska E. Rohrer
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
High Pressures ◽  
Ambient Pressure ◽  
Close Packing ◽  
Hexagonal Close Packing ◽  
Rietveld Refinements ◽  
X Ray ◽  
Anion Coordination ◽  
Diamond Anvil

The ReO3-type structure NbO2F, niobium dioxyfluoride, has been studied at high pressures using diamond anvil cells and synchrotron X-ray radiation. High-pressure powder diffraction measurements have been performed up to 40.1 GPa. A phase transition from the cubic (Pm3¯m) ambient pressure structure to a rhombohedral (R3¯c) structure at 0.47 GPa has been observed. Rietveld refinements at 1.38, 1.96, 3.20, 6.23, 9.00 and 10.5 GPa showed that the transition involves an a − a − a − tilting of the cation–anion coordination octahedra and a change of the anion–anion arrangement to approach hexagonal close packing. Compression and distortion of the Nb(O/F)6 octahedra is also revealed by the Rietveld refinements. At 17–18 GPa, the diffraction pattern disappears and the structure becomes X-ray amorphous.

scholarly journals Synthesis of α-cristobalite-type CO2-SiO2under extreme conditions

2014 ◽  
Vol 70 (a1) ◽  
pp. C753-C753
Author(s):  
Julien Haines ◽  
Mario Santoro ◽  
Federico Gorelli ◽  
Roberto Bini ◽  
Olivier Cambon ◽  
...  
Keyword(s):  
Solid Solution ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Metastable Phase ◽  
Ambient Pressure ◽  
Small Variation ◽  
Unit Cell ◽  
Extreme Conditions ◽  
Oxygen Sublattice ◽  
Compact Structure

Extreme conditions change the behavior and reactivity of elements and compounds and permit the synthesis of novel materials. In the case of group IV oxides, molecular CO2and a network solid silica, which were considered to be incompatible, are found to react under HP-HT conditions. A crystalline CO2-SiO2solid solution was synthesized from molecular CO2and microporous silicalite SiO2at 16-22 GPa and temperatures above 4000 K in a laser heated diamond anvil cell [1]. Synchrotron X-ray diffraction data show that the crystal adopts a densely packed α-cristobalite structure (space group P41212) with carbon and silicon in 4-fold coordination. This occurs at pressures at which SiO2normally adopts a 6-fold coordinated rutile-type stishovite structure. The P-T conditions used in this study represent a compromise between the respective stabilities of 3- and 4-fold coordination in CO2and 4- and 6-fold coordination in SiO2. This solid solution can be recovered at ambient pressure at which the unit cell volume is 26% lower than that of α-cristobalite SiO2. This is due to the incorporation of much smaller carbon atoms, resulting in the collapse of the oxygen sublattice. The unit cell volume and the different C and Si sites identified in Raman spectroscopy are consistent with a C:Si ratio of 6(1):4(1). The tetragonal c/a ratio increases from 1.283 at 16 GPa to 1.303 at ambient pressure and is lower than that of SiO2due to the more compact structure of the new material and essentially corresponds to that of the dense rutile-type oxygen sublattice. This can explain the small variation in volume observed for this phase corresponding to a bulk modulus of about 240 GPa. Due to the incorporation of silicon atoms, this hard solid based on CO4tetrahedra can be retained as a metastable phase. This strongly modifies standard oxide chemistry and shows that carbon can enter silica giving rise to a new class of hard, light, carbon-rich oxide materials with novel physical properties.

Valence Crossover of Ce Ions in CeCu2Si2 under High Pressure –Pressure Dependence of the Unit Cell Volume and the NQR Frequency–

2013 ◽  
Vol 82 (11) ◽  
pp. 114701 ◽  
Author(s):  
Tatsuo C. Kobayashi ◽  
Kenji Fujiwara ◽  
Keiki Takeda ◽  
Hisatomo Harima ◽  
Yoichi Ikeda ◽  
...  
Keyword(s):  
High Pressure ◽  
Cell Volume ◽  
Pressure Dependence ◽  
Unit Cell Volume ◽  
Unit Cell

High-pressure phase transformation in MnCO3: a synchrotron XRD study

2006 ◽  
Vol 71 (1) ◽  
pp. 105-111 ◽  
Author(s):  
S. Ono
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Unit Cell ◽  
Manganese Carbonate ◽  
Orthorhombic Unit Cell ◽  
Direct Formation ◽  
Diamond Anvil ◽  
Pressure Form ◽  
Compression Data ◽  
Laser Heated

AbstractThe high-pressure behaviour of manganese carbonate was investigated by in situ synchrotron X-ray powder diffraction up to 54 GPa with a laser-heated diamond anvil cell. A phase transition from rhodochrosite to a new structure form was observed at 50 GPa after laser heating. The diffraction pattern of the new high-pressure form was reasonably indexed with an orthorhombic unit-cell with a = 5.361 A, b = 8.591 A and c = 9.743 Å. The pressure-induced phase transition implies a unit-cell volume reduction of ∼5%. This result does not support the direct formation of diamond by dissociation of solid state MnCO3 reported in a previous study. Fitting the compression data of rhodochrosite to a second-order Birch-Murnaghan equation of state (Ko’ = 4) gives K0 = 126(±10) GPa. The c axis of the unit-cell parameter was more compressive than the a axis.

Atomic displacements at and order of all phase transitions in multiferroic YMnO3 and BaTiO3

2009 ◽  
Vol 65 (4) ◽  
pp. 450-457 ◽  
Author(s):  
S. C. Abrahams
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Landau Theory ◽  
Unit Cell ◽  
Paramagnetic Phase ◽  
First Order ◽  
Atomic Displacements ◽  
Magnetic Symmetry

Coordinate analysis of the multiple phase transitions in hexagonal YMnO3 leads to the prediction of a previously unknown aristotype phase, with the resulting phase-transition sequence: P63′cm′(e.g.) ↔ P63 cm ↔ P63/mcm ↔ P63/mmc ↔ P6/mmm. Below the Néel temperature T N ≃ 75 K, the structure is antiferromagnetic with the magnetic symmetry not yet determined. Above T N the P63 cm phase is ferroelectric with Curie temperature T C ≃ 1105 K. The nonpolar paramagnetic phase stable between T C and ∼ 1360 K transforms to a second nonpolar paramagnetic phase stable to ∼ 1600 K, with unit-cell volume one-third that below 1360 K. The predicted aristotype phase at the highest temperature is nonpolar and paramagnetic, with unit-cell volume reduced by a further factor of 2. Coordinate analysis of the three well known phase transitions undergone by tetragonal BaTiO3, with space-group sequence R3m ↔ Amm2 ↔ P4mm ↔ Pm\overline 3m, provides a basis for deriving the aristotype phase in YMnO3. Landau theory allows the I ↔ II, III ↔ IV and IV ↔ V phase transitions in YMnO3, and also the I ↔ II phase transition in BaTiO3, to be continuous; all four, however, unambiguously exhibit first-order characteristics. The origin of phase transitions, permitted by theory to be second order, that are first order instead have not yet been thoroughly investigated; several possibilities are briefly considered.

Pressure Tuning of Crystalline As2Te3

2004 ◽  
Vol 848 ◽  
Author(s):  
T. J. Scheidemantel ◽  
J. F. Meng ◽  
J. V. Badding
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Thermoelectric Power ◽  
Diamond Anvil Cell ◽  
Ambient Pressure ◽  
Structural Phase ◽  
Absolute Value ◽  
Pressure Tuning ◽  
Diamond Anvil ◽  
Pressure Phase

ABSTRACTWe report the pressure dependence of the thermoelectric power of As2Te3. Pressures up to 10 GPa were induced using a Mao-Bell diamond anvil cell. The absolute value of the thermoelectric power dropped from S ≈ 230μV/K at ambient pressure to S ≈ 75 GPa near 5 GPa. At 6 GPa it then increased rapidly to S ≈ 220βV/K. This behavior is indicative of a structural phase transition as suggested by previously published high pressure phase diagrams.

Enantiotropic phase transition in a binuclear tin complex with anO,N,O′-tridentate ligand

2013 ◽  
Vol 69 (11) ◽  
pp. 1336-1339 ◽  
Author(s):  
Anke Schwarzer ◽  
Lydia E. H. Paul ◽  
Uwe Böhme
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Tridentate Ligand ◽  
Asymmetric Unit ◽  
Disorder Transition ◽  
Vinyl Group

The crystal structure of chlorido{μ-2-[(2-oxidobenzylidene)amino]ethanolato-κ4O,N,O′:O′}{2-[(2-oxidobenzylidene)amino]ethanolato-κ3O,N,O′}trivinylditin(IV), [Sn2(C2H3)3(C9H9NO2)2Cl], is disordered above 178 K. A doubling of the unit-cell volume is observed on cooling. The asymmetric unit at 93 K contains two ordered molecules. The phase transition corresponds to an order–disorder transition of one vinyl group bound to the SnIVatom.

scholarly journals Geometric considerations of the monoclinic–rutile structural transition in VO2

2019 ◽  
Vol 48 (25) ◽  
pp. 9260-9265
Author(s):  
Shian Guan ◽  
Aline Rougier ◽  
Matthew R. Suchomel ◽  
Nicolas Penin ◽  
Kadiali Bodiang ◽  
...  
Keyword(s):  
Phase Transition ◽  
Cell Volume ◽  
Unit Cell Volume ◽  
Structural Transition ◽  
Unit Cell

Geometrical and experimental examinations of VO2 show how hysteretic phase transition phenomena across the MIT can be driven by positive crystal energy effects of increasing unit cell volume.

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