Structures and Phase Transitions of the A 7PSe6 (A = Ag, Cu) Argyrodite-Type Ionic Conductors. I. Ag7PSe6

1998 ◽  
Vol 54 (4) ◽  
pp. 376-383 ◽  
Author(s):  
M. Evain ◽  
E. Gaudin ◽  
F. Boucher ◽  
V. Petricek ◽  
F. Taulelle
Keyword(s):  
Phase Transition ◽  
Atomic Displacement ◽  
Ionic Conductors ◽  
Reliability Factor ◽  
Conducting Phase ◽  
Cubic Symmetry ◽  
Space Group ◽  
Ionic Conducting ◽  
Jahn Teller ◽  
Diffusion Paths

The crystal structures of the two polymorphic forms of the argyrodite Ag7PSe6 compound are analysed by means of single-crystal X-ray diffraction. Above the phase transition at 453 K leading to the ionic conducting phase, γ-Ag7PSe6 crystallizes in cubic symmetry, space group F4¯3m, with a = 10.838 (3) Å, V = 1273.1 (12) Å3 and Z = 4 at 473 K. The refinement of the 473 K structure leads to a reliability factor of R = 0.0326 for 192 independent reflections and 33 variables. Diffusion paths for silver d 10 ions are evidenced by means of a combination of a Gram–Charlier development of the atomic displacement factors and a split model. Below the phase transition β-Ag7PSe6 crystallizes again in cubic symmetry, but with the space group P213 and a = 10.772 (2) Å, V = 1250.1 (6) Å3 and Z = 4 at room temperature. The refinement of the 293 K structure leads to a reliability factor of R = 0.0267 for 1125 independent reflections and 68 variables. In the β-Ag7PSe6 ordered phase the silver cations are found in various sites corresponding to the most pronounced probability density locations of the high-temperature diffusion paths. Those positions correspond to low coordination (2, 3 and 4) sites, in agreement with the silver preference for such environments. In addition, the Ag atoms are found slightly displaced from the true linear, triangular or tetrahedral coordination, as expected from second-order Jahn–Teller effects.

Structures and phase transitions of the A 7PSe6 (A = Ag, Cu) argyrodite-type ionic conductors. II. β- and γ-Cu7PSe6

2000 ◽  
Vol 56 (3) ◽  
pp. 402-408 ◽  
Author(s):  
E. Gaudin ◽  
F. Boucher ◽  
V. Petricek ◽  
F. Taulelle ◽  
M. Evain
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Partial Ordering ◽  
Temperature Phase ◽  
Intermediate Form ◽  
Ionic Conductors ◽  
Conducting Phase ◽  
Cubic Symmetry ◽  
Space Group ◽  
Diffusion Paths

The crystal structures of two of the three polymorphic forms of the Cu7PSe6 argyrodite compound are determined by means of single-crystal X-ray diffraction. In the high-temperature form, at 353 K, i.e. 33 K above the first phase transition, γ-Cu7PSe6 crystallizes in cubic symmetry, space group F4¯3m. The full-matrix least-squares refinement of the structure leads to the residual factors R  = 0.0201 and wR = 0.0245 for 31 parameters and 300 observed independent reflections. In the intermediate form, at room temperature, β-Cu7PSe6 crystallizes again in cubic symmetry, but with space group P213. Taking into account a merohedric twinning, the refinement of the β-Cu7PSe6 structure leads to the residual factors R  = 0.0297 and wR  = 0.0317 for 70 parameters and 874 observed, independent reflections. The combination of a Gram–Charlier development of the Debye–Waller factor and a split model for copper cations reveals the possible diffusion paths of the d 10 species in the γ-Cu7PSe6 ionic conducting phase. The partial ordering of the Cu+ d 10element at the phase transition is found in concordance with the highest probability density sites of the high-temperature phase diffusion paths. A comparison between the two Cu7PSe6 and Ag7PSe6 analogues is carried out, stressing the different mobility of Cu+ and Ag+ and their relative stability in low-coordination chalcogenide environments.

Structure and phase transition of the Se-rich variety of antimonpearceite, [(Ag,Cu)6(Sb,As)2(S,Se)7][Ag9Cu(S,Se)2Se2]

2006 ◽  
Vol 62 (5) ◽  
pp. 768-774 ◽  
Author(s):  
Michel Evain ◽  
Luca Bindi ◽  
Silvio Menchetti
Keyword(s):  
Phase Transition ◽  
Room Temperature ◽  
Atomic Displacement ◽  
X Ray Diffraction ◽  
X Ray ◽  
Dimensional Diffusion ◽  
Ionic Conducting ◽  
Local Arrangement ◽  
Diffusion Paths ◽  
Linear Coordination

The crystal structure of a Se-rich antimonpearceite has been solved and refined by means of X-ray diffraction data collected at temperatures above (room temperature) and below (120 K) an ionic conductivity-induced phase transition. Both structure arrangements consist of the stacking of [(Ag,Cu)6(Sb,As)2(S,Se)7]2− A (A′) and [Ag9Cu(S,Se)2Se2]2+ B (B′) module layers in which Sb forms isolated SbS3 pyramids typically occurring in sulfosalts; copper links two S atoms in a linear coordination, and silver occupies sites with coordination ranging from quasi-linear to almost tetrahedral. In the ionic-conducting form, at room temperature, the silver d 10 ions are found in the B (B′) module layer along two-dimensional diffusion paths and their electron densities described by means of a combination of a Gram–Charlier development of the atomic displacement factors and a split-atom model. The structure resembles that of pearceite, except for the presence of both specific (Se) and mixed (S, Se) sites. In the low-temperature `ordered' phase at 120 K the silver d 10 ions of the B (B′) module layer are located in well defined sites with mixed S—Se coordination ranging from quasi-linear to almost tetrahedral. The structure is then similar to that of 222-pearceite but with major differences, specifically its cell metric, symmetry and local arrangement in the B (B′) module layer.

Structural aspects of thermal properties of AgCuS compound

2020 ◽  
Vol 34 (05) ◽  
pp. 2050066 ◽  
Author(s):  
Y. I. Aliyev ◽  
Y. G. Asadov ◽  
T. M. Ilyasli ◽  
F. M. Mammadov ◽  
T. G. Naghiyev ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Central Peak ◽  
Orthorhombic Symmetry ◽  
Cubic Symmetry ◽  
Space Group ◽  
Temperature Ranges ◽  
Structural Aspects

The crystal structure and thermal properties of AgCuS compound were investigated at high temperature ranges. It was found that the crystal structure of these compounds has orthorhombic symmetry with Cmcm space group at the normal condition and room temperature. The phase transition to cubic symmetry with Fm3m space group is observed at [Formula: see text] temperature. The endoeffect was observed with a central peak at [Formula: see text] in the differential thermal analysis. The temperature dependence on heat capacity was obtained in the range of [Formula: see text] temperature. Thermodynamic parameters have been determined: enthalpy and heat capacity. The value of enthalpy was calculated according to the temperature of the phase transition.

Crystal structure refinements of tetragonal (OH,F)-rich spessartine and henritermierite garnets

2018 ◽  
Vol 74 (1) ◽  
pp. 104-114 ◽  
Author(s):  
Sytle M. Antao ◽  
Laura A. Cruickshank
Keyword(s):  
Large Deviation ◽  
Scattered Electron ◽  
Cubic Symmetry ◽  
Oh Groups ◽  
Space Group ◽  
Space Groups ◽  
Cell Parameters ◽  
Jahn Teller ◽  
Homogeneous Composition ◽  
Cation Sites

Cubic garnet (space group Ia\overline 3 d) has the general formula X 3 Y 2 Z 3O12, where X, Y and Z are cation sites. In the tetragonal garnet (space group I41/acd), the corresponding cation sites are X1 and X2, Y, and Z1 and Z2. In both space groups only the Y site is the same. The crystal chemistry of a tetragonal (OH,F)-rich spessartine sample from Tongbei, near Yunxiao, Fujian Province, China, with composition X (Mn2.82Fe^{2+}_{0.14}Ca0.04)Σ3 Y {Al1.95Fe^{3+}_{0.05}}Σ2 Z [(SiO4)2.61(O4H4)0.28(F4)0.11]Σ3 (Sps94Alm5Grs1) was studied with single-crystal X-ray diffraction and space group I41/acd. The deviation of the unit-cell parameters from cubic symmetry is small [a = 11.64463 (1), c = 11.65481 (2) Å, c/a = 1.0009]. Point analyses and back-scattered electron images, obtained by electron-probe microanalysis, indicate a homogeneous composition. The Z2 site is fully occupied, but the Z1 site contains vacancies. The occupied Z1 and Z2 sites with Si atoms are surrounded by four O atoms, as in anhydrous cubic garnets. Pairs of split sites are O1 with F11 and O2 with O22. When the Z1 site is vacant, a larger [(O2H2)F2] tetrahedron is formed by two OH and two F anions in the O22 and F11 sites, respectively. This [(O2H2)F2] tetrahedron is similar to the O4H4 tetrahedron in hydrogarnets. These results indicate ^{X}{{\rm Mn}^ {2+}_{3}}\,^{Y}{\rm Al}_{2}^{Z}[({\rm SiO}_{4})_{2}({\rm O}_{2}{\rm H}_{2})_{0.5}({\rm F}_{2})_{0.5}]_{\Sigma3} as a possible end member, which is yet unknown. The H atom that is bonded to the O22 site is not located because of the small number of OH groups. In contrast, tetragonal henritermierite, ideally ^{X}{\rm Ca}_{3}\,^{Y}{\rm Mn}^{3+}_{2}\,^{Z}[({\rm SiO}_{4})_{2}({\rm O}_{4}{\rm H}_{4})_1]_{\Sigma3}, has a vacant Z2 site that contains the O4H4 tetrahedron. The H atom is bonded to an O3 atom [O3—H3 = 0.73 (2) Å]. Because of O2—Mn3+—O2 Jahn–Teller elongation of the Mn3+O6 octahedron, a weak hydrogen bond is formed to the under-bonded O2 atom. This causes a large deviation from cubic symmetry (c/a = 0.9534).

scholarly journals In situ observation of the tetragonal–cubic phase transition in the CeZrO4 solid solution – a high-temperature neutron diffraction study

2007 ◽  
Vol 63 (3) ◽  
pp. 384-389 ◽  
Author(s):  
Takahiro Wakita ◽  
Masatomo Yashima
Keyword(s):  
Phase Transition ◽  
Solid Solution ◽  
Neutron Diffraction ◽  
Axial Ratio ◽  
Rietveld Analysis ◽  
Atomic Displacement ◽  
Cubic Phase ◽  
In Situ Observation ◽  
Space Group

The crystal structure of the compositionally homogeneous ceria–zirconia solid solution CeZrO4 is refined by Rietveld analysis of neutron diffraction data measured in situ over the temperature range 296–1831 K. The CeZrO4 exhibits a tetragonal structure with the space group P42/nmc at temperatures from 296 to 1542 K (Z = 1), and a cubic fluorite-type form with the space group Fm\overline 3 m at 1831 K (Z = 2). The isotropic atomic displacement parameters of Ce and Zr atoms B(Ce,Zr) and O atoms B(O) are found to increase with temperature, with B(O) being larger than B(Ce,Zr), suggesting the higher diffusivity of oxygen ions. The ratio of the c axial length to the a length of the pseudo-fluorite lattice (c/a F axial ratio) for the tetragonal CeZrO4 phase increased from 296 to 1034 K and decreased from 1291 to 1542 K, reaching unity between 1542 and 1831 K. The displacement of O atoms along the c axis in the tetragonal CeZrO4 phase increased from 296 to 1034 K and decreased from 1291 to 1542 K, reaching 0.0 Å between 1542 and 1831 K. These results indicate that the cubic-to-tetragonal phase transition between 1542 and 1831 K is accompanied by oxygen displacement along the c axis and the increase of the c/a F axial ratio from unity.

Crystal structure and structural phase transition in bismuth-containing HoFe3(BO3)4 in the temperature range 11–500 K

2019 ◽  
Vol 75 (6) ◽  
pp. 954-968 ◽  
Author(s):  
Ekaterina S. Smirnova ◽  
Olga A. Alekseeva ◽  
Alexander P. Dudka ◽  
Dmitry N. Khmelenin ◽  
Kirill V. Frolov ◽  
...  
Keyword(s):  
Phase Transition ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Local Environment ◽  
Atomic Displacement ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Atomic Displacement Parameters ◽  
Thermal Vibrations

An accurate single-crystal X-ray diffraction study of bismuth-containing HoFe3(BO3)4 between 11 and 500 K has revealed structural phase transition at T str = 365 K. The Bi atoms enter the composition from Bi2Mo3O12-based flux during crystal growth and significantly affect T str. The content of Bi was estimated by two independent methods, establishing the composition as (Ho0.96Bi0.04)Fe3(BO3)4. In the low-temperature (LT) phase below T str the (Ho0.96Bi0.04)Fe3(BO3)4 crystal symmetry is trigonal, of space group P3121, whereas at high temperature (HT) above 365 K the symmetry increases to space group R32. There is a sharp jump of oxygen O1 (LT) and O2 (LT) atomic displacement parameters (ADP) at T str. O1 and O2 ADP ellipsoids are the most elongated over 90–500 K. In space group R32 specific distances decrease steadily or do not change with decreasing temperature. In space group P3121 the distortion of the polyhedra Ho(Bi)O6, Fe1O6 and Fe2O6, B2O3 and B3O3 increases with decreasing temperature, whereas the triangles B1O3 remain almost equilateral. All BO3 triangles deviate from the ab plane with decreasing temperature. Fe–Fe distances in Fe1 chains decrease, while distances in Fe2 chains increase with decreasing temperature. The Mössbauer study confirms that the FeO6 octahedra undergo complex dynamic distortions. However, all observed distortions are rather small, and the general change in symmetry during the structural phase transition has very little influence on the local environment of iron in oxygen octahedra. The Mössbauer spectra do not distinguish two structurally different Fe1 and Fe2 positions in the LT phase. The characteristic temperatures of cation thermal vibrations were calculated using X-ray diffraction and Mössbauer data.

Crystal structure, phase transition and structural deformations in iron borate (Y0.95Bi0.05)Fe3(BO3)4in the temperature range 90–500 K

2018 ◽  
Vol 74 (2) ◽  
pp. 226-238 ◽  
Author(s):  
Ekaterina S. Smirnova ◽  
Olga A. Alekseeva ◽  
Alexander P. Dudka ◽  
Vladimir V. Artemov ◽  
Yan V. Zubavichus ◽  
...  
Keyword(s):  
Phase Transition ◽  
Structural Characteristics ◽  
Structural Phase ◽  
Atomic Displacement ◽  
Coordination Polyhedra ◽  
Space Group ◽  
Temperature Range ◽  
Trigonal Structure ◽  
Iron Borates ◽  
Structure Phase Transition

An accurate X-ray diffraction study of (Y0.95Bi0.05)Fe3(BO3)4single crystals in the temperature range 90–500 K was performed on a laboratory diffractometer and used synchrotron radiation. It was established that the crystal undergoes a diffuse structural phase transition in the temperature range 350–380 K. The complexity of localization of such a transition over temperature was overcome by means of special analysis of systematic extinction reflections by symmetry. The transition temperature can be considered to beTstr≃ 370 K. The crystal has a trigonal structure in the space groupP3121 at temperatures of 90–370 K, and it has a trigonal structure in the space groupR32 at 375–500 K. There is one type of chain formed by the FeO6octahedra along thecaxis in theR32 phase. When going into theP3121 phase, two types of nonequivalent chains arise, in which Fe atoms are separated from the Y atoms by a different distance. Upon lowering the temperature from 500 to 90 K, a distortion of the Y(Bi)O6, FeO6, B(2,3)O3coordination polyhedra is observed. The distances between atoms in helical Fe chains and Fe—O—Fe angles change non-uniformly. A sharp jump in the equivalent isotropic displacement parameters of O1 and O2 atoms within the Fe—Fe chains and fluctuations of the equivalent isotropic displacement parameters of B2 and B3 atoms were observed in the region of structural transition as well as noticeable elongation of O1, O2, B2, B3, Fe1, Fe2 atomic displacement ellipsoids. It was established that the helices of electron density formed by Fe, O1 and O2 atoms may be structural elements determining chirality, optical activity and multiferroicity of rare-earth iron borates. Compression and stretching of these helices account for the symmetry change and for the manifestation of a number of properties, whose geometry is controlled by an indirect exchange interaction between iron cations that compete with the thermal motion of atoms in the structure. Structural analysis detected these changes as variations of a number of structural characteristics in thecunit-cell direction, that is, the direction of the helices. Structural results for the local surrounding of the atoms in (Y0.95Bi0.05)Fe3(BO3)4were confirmed by EXAFS and Mössbauer spectroscopies.

scholarly journals Crystal and electronic structure engineering of tin monoxide by external pressure

2021 ◽  
Author(s):  
Kun Li ◽  
Junjie Wang ◽  
Vladislav A. Blatov ◽  
Yutong Gong ◽  
Naoto Umezawa ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Band Gap ◽  
High Pressures ◽  
Low Pressure ◽  
Widespread Application ◽  
Space Group ◽  
Tin Monoxide ◽  
High Possibility ◽  
Pressure Phase

AbstractAlthough tin monoxide (SnO) is an interesting compound due to its p-type conductivity, a widespread application of SnO has been limited by its narrow band gap of 0.7 eV. In this work, we theoretically investigate the structural and electronic properties of several SnO phases under high pressures through employing van der Waals (vdW) functionals. Our calculations reveal that a metastable SnO (β-SnO), which possesses space group P21/c and a wide band gap of 1.9 eV, is more stable than α-SnO at pressures higher than 80 GPa. Moreover, a stable (space group P2/c) and a metastable (space group Pnma) phases of SnO appear at pressures higher than 120 GPa. Energy and topological analyses show that P2/c-SnO has a high possibility to directly transform to β-SnO at around 120 GPa. Our work also reveals that β-SnO is a necessary intermediate state between high-pressure phase Pnma-SnO and low-pressure phase α-SnO for the phase transition path Pnma-SnO →β-SnO → α-SnO. Two phase transition analyses indicate that there is a high possibility to synthesize β-SnO under high-pressure conditions and have it remain stable under normal pressure. Finally, our study reveals that the conductive property of β-SnO can be engineered in a low-pressure range (0–9 GPa) through a semiconductor-to-metal transition, while maintaining transparency in the visible light range.

scholarly journals Pressure-induced Jahn-Teller Switch in the Homoleptic Hybrid Perovskite [(CH3)2NH2]Cu(HCOO)3: Orbital Reordering by Unconventional Degrees of Freedom

2021 ◽  
Author(s):  
Rebecca Scatena ◽  
Michał Andrzejewski ◽  
Roger D Johnson ◽  
Piero Macchi
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Coordination Polymer ◽  
Degrees Of Freedom ◽  
X Ray Diffraction ◽  
X Ray ◽  
Hybrid Perovskite ◽  
Jahn Teller

Through in-situ, high-pressure x-ray diffraction experiments we have shown that the homoleptic perovskite-like coordination polymer [(CH3)2NH2]Cu(HCOO)3 undergoes a pressure-induced orbital reordering phase transition above 5.20 GPa. This transition is distinct...

NQR and Crystal Structure of 4,5-Dichloroimidazole, C3H2N2Cl2

1992 ◽  
Vol 47 (1-2) ◽  
pp. 177-181 ◽  
Author(s):  
Shi-Qi Dou ◽  
Alarich Weiss
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Temperature Dependence ◽  
Room Temperature ◽  
Unit Cell ◽  
Space Group ◽  
Temperature Range ◽  
Temperature Coefficients ◽  
Group D

AbstractThe two line 35Cl NQR spectrum of 4,5-dichloroimidazole was measured in the temperature range 77≦ T/K ≦ 389. The temperature dependence of the NQR frequencies conforms with the Bayer model and no phase transition is indicated in the curves v ( 35Cl)= f(T). Also the temperature coefficients of the 35Cl NQR frequencies are "normal". At 77 K the 35Cl NQR frequencies are 37.409 MHz and 36.172 MHz and at 389 K 35.758 MHz and 34.565 MHz. The compound crystallizes at room temperature with the tetragonal space group D44-P41212, Z = 8 molecules per unit cell; at 295 K : a = 684.2(5) pm, c = 2414.0(20) pm. The relations between the crystal structure and the NQR spectrum are discussed.

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