Search results for "tetragonal crystal"
showing 10 items of 216 documents
Pressure-induced structural and semiconductor-semiconductor transitions in Co0.5Mg0.5Cr2O4
2018
The effect of pressure on the structural, vibrational, and electronic properties of Mg-doped Cr bearing spinel $\mathrm{C}{\mathrm{o}}_{0.5}\mathrm{M}{\mathrm{g}}_{0.5}\mathrm{C}{\mathrm{r}}_{2}{\mathrm{O}}_{4}$ was studied up to 55 GPa at room-temperature using x-ray diffraction, Raman spectroscopy, electrical transport measurements, and ab initio calculations. We found that the ambient-pressure phase is cubic (spinel-type, $Fd\overline{3}m$) and underwent a pressure-induced structural transition to a tetragonal phase (space group $I\overline{4}m2$) above 28 GPa. The ab initio calculation confirmed this first-order phase transition. The resistivity of the sample decreased at low pressures …
Pressure-induced order–disorder transitions in β-In2S3: an experimental and theoretical study of structural and vibrational properties
2021
This joint experimental and theoretical study of the structural and vibrational properties of β-In2S3 upon compression shows that this tetragonal defect spinel undergoes two reversible pressure-induced order-disorder transitions up to 20 GPa. We propose that the first high-pressure phase above 5.0 GPa has the cubic defect spinel structure of α-In2S3 and the second high-pressure phase (ϕ-In2S3) above 10.5 GPa has a defect α-NaFeO2-type (R3m) structure. This phase, related to the NaCl structure, has not been previously observed in spinels under compression and is related to both the tetradymite structure of topological insulators and to the defect LiTiO2 phase observed at high pressure in oth…
High-pressure electronic structure and phase transitions in monoclinic InSe: X-ray diffraction, Raman spectroscopy, and density functional theory
2008
We have studied the crystal and electronic structure of monoclinic (MC) InSe under pressure finding a reversible phase transition to a ${\mathrm{Hg}}_{2}{\mathrm{Cl}}_{2}$-like tetragonal phase. The pressure evolution of the crystal structure was investigated by angle-dispersive x-ray diffraction and Raman spectroscopy in a diamond-anvil cell up to $30\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. From the diffraction experiments, we deduced that MC InSe becomes gradually more symmetric under pressure, transforming the crystal structure into a tetragonal one at $19.4\ifmmode\pm\else\textpm\fi{}0.5\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. This phase transition occurs without any volume change. Ra…
Crystal polymorphism of (μ4–O)-body centered adamantanoid Cu(II) complexes
2016
Abstract Two novel polymorphs of [Cu4(μ4–O)(μ–Cl)6(DASO)4], (DASO = diallyl sulfoxide; C6H10OS), rhombic (C) and triclinic (D), were obtained and examined by single crystal X-ray diffraction analysis at two temperatures, 295(2) and 100(1) K. This study, in addition to our recent work on the tetragonal (A) and trigonal (B) forms of the title compound, allowed determining the nature of polymorphism and temperature-induced phase transitions. It is stated that both the packing arrangement and the displacive transformation integrate these structures, forming the symmetrically and thermodynamically related series: A,B → C → D. The C3h → C4 distortion of Cu(II) trigonal bipyramidal coordination ge…
Guest Modulation of Spin-Crossover Transition Temperature in a Porous Iron(II) Metal Organic Framework: Experimental and Periodic DFT Studies
2014
The synthesis, structure, and magnetic properties of three clathrate derivatives of the spin-crossover porous coordination polymer {Fe(pyrazine)[Pt(CN)(4)]} (1) with five-membered aromatic molecules furan, pyrrole, and thiophene is reported. The three derivatives have a cooperative spin-crossover transition with hysteresis loops 14-29 K wide and average critical temperatures T-c=201 K (1.fur), 167 K (1.pyr), and 114.6 K (1.thio) well below that of the parent compound 1 (T-c=295 K), confirming stabilization of the HS state. The transition is complete and takes place in two steps for 1.fur, while 1.pyr and 1.thio show 50% spin transition. For 1.fur the transformation between the HS and IS (mi…
Comparative studies of ferroelectric and magnetic phase transitions in Pb(Fe1/2Nb1/2)O3-PbMO3 (M-Ti, Zr) multiferroic solid solutions
2015
Some peculiar features of magnetic x,T-phase diagram of (1-x)PbFe1/2Nb1/2O3- xPbTiO3 system at x ≈ 0.1 have been ascribed previously to the change of the lattice symmetry from rhombohedral to tetragonal or to the decrease of the lattice parameter with x. We carried out structural, dielectric, magnetization, and Mossbauer studies of (1-x)PbFe1/2Nb1/2O3-xPbZrO3 system, where the symmetry remains rhombohedral, while the lattice parameter increases with x. However, the magnetic x,T-phase diagram of (1-x)PbFe1/2Nb1/2O3-xPbZrO3 appeared to be very similar to that of (1-x) PbFe1/2Nb1/2O3-xPbTiO3. Anomalies of composition dependence of magnetic phase transition temperatures at x ≈ 0.1 are supposed …
An EPR investigation of the phase transitions and cooperative ordering phenomena of pentaamminecopper(II) polyhedra in Cu(NH3)5X2 [X=BF4, CIO4; Br]
1996
The results of powder and single-crystal EPR studies on Cu(NH3)5X2 compounds [X=BF4, CIO4; Br] give evidence that phase transitions from a cubic α-phase (g i ≃2.12) with an anti-K2PtCl6 type structure to low-temperature β-phases with reduced symmetry occur, which are induced by ordering processes of the vacancies □ of elongated [Cu(NH3)5□]2+ pseudo-octahedra. The type of order is crucially controlled, by the nature of the anion. In the case of the BF 4 − and ClO 4 − salts the large anions are structure-determining leading to a slightly disturbed antiferrodistortive order of the elongated CuIIN5 square pyramids atT c≃155 K and <130 K, respectively. The resulting pseudo-tetragonal β-structure…
Neutron diffraction experiments on UCu4+xAl8−x
1992
Abstract Neutron diffraction experiments are reported on UCu4+xAl8−x for concentrations 0.1≤ x ≤1.9 and temperatures 1.6 K≤T≤300 K. For x ≤ 1 these compounds undergo antiferromagnetic phase transitions into a collinear AF I-type structure. with the magnetic moments aligned along the tetragonal c-axis and alternating order within the a−b planes. With increasing concentration the ordering temperatures decrease and moment compensation due to a Kondo-type interaction develops for x>1.
LaAg x In1?x
1980
The phonon dispersion of LaAg x In1−x (x=1, 0.89, 0.8) has been studied by inelastic neutron scattering in the cubic high temperature phase. A soft mode behaviour was observed at theM-point. The doubling and the cubic to tetragonal deformation of the elementary cell was observed through the phase transition. The measurements of the elastic constants were extended to 450 K and their magnetic field dependence was investigated.
Structure and properties of high piezoelectric coupling Pb(B′½Nb½)O3-PbTiO3binary systems
1999
Abstract The (1-x)Pb(Lu½ Nb½)O3-xPbTiO3 and (1-x)Pb(Er½ Nb½)O3-xPbTiO3 binary systems have been obtained, the structure and properties of which are studied. The unit cell of erbium niobate (PErN) is described as pseudomonoclinic of orthorhombic Bmm2 symmetry: a=c=4.2161 A b=4.0869 A β=90.55° and composition is characterized with antiferroelectric phase transition at 305°C. The PErNT system has the morphotropic phase region extending over the x=0.4–0.6 interval. In PLuNT ceramics system the pseudomonoclinic phase structure Bmm2 extending over the 0≤x ≤0.38 interval becomes pseudocubic at x≈ 0.2. The morphotropic region is spread over 0.38< × < 0.49; at higher PT concentrations (1.0 ≥ × ≥ 0.4…