Structural phase transition of CeAuGe at high pressure

2005 ◽  
Vol 220 (2/3) ◽  
Author(s):  
Valeri Brouskov ◽  
Michael Hanfland ◽  
Rainer Pöttgen ◽  
Ulrich Schwarz
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Structural Phase ◽  
Lattice Parameter ◽  
First Order ◽  
First Order Phase Transition ◽  
Diamond Anvil ◽  
Ternary Intermetallic Compound ◽  
First Order Phase ◽  
Type Crystal

AbstractStructural properties of the ternary intermetallic compound CeAuGe were investigated at hydrostatic pressures up to 15 GPa with high-resolution angle dispersive X-ray powder diffraction using synchrotron radiation and the diamond anvil cell technique. At 8.7(7) GPa a first order phase transition is observed from a hexagonal NdPtSb-type arrangement into an orthorhombic high-pressure modification with a TiNiSi-type crystal structure. The transformation is associated with a 3% shortening of the lattice parameter perpendicular to the puckered layers [AuGe]

scholarly journals Спектры пропускания монокристаллов гибридных перовскитов MAPbI-=SUB=-3-=/SUB=- вблизи края фундаментального поглощения

2022 ◽  
Vol 130 (1) ◽  
pp. 116
Author(s):  
В.Е. Аникеева ◽  
К.Н. Болдырев ◽  
О.И. Семенова ◽  
М.Н. Попова
Keyword(s):  
Phase Transition ◽  
Absorption Edge ◽  
Structural Phase ◽  
Fundamental Absorption Edge ◽  
Orthorhombic Phase ◽  
Temperature Hysteresis ◽  
First Order ◽  
Hybrid Perovskite ◽  
First Order Phase Transition ◽  
First Order Phase

The paper presents the transmission spectra of hybrid perovskite MAPbI3 single crystals near the fundamental absorption edge in a wide temperature range. The absorption coefficient α of the single crystal samples is estimated at a temperature T = 150 K for the light with a photon energy E = 1.6 eV and at T = 40 K for E = 1.8 eV. The obtained values turned out to be several orders of magnitude smaller than the values of α for thin-film samples known from the literature. A sharp shift of the fundamental absorption edge by ~ 100 meV was observed at a temperature T1 = 160 K of the structural phase transition from the tetragonal to the orthorhombic phase. The temperature hysteresis of the shift of the fundamental absorption edge near T1 was recorded, which is characteristic of a first-order phase transition.

scholarly journals Crystal structure of the high-pressure phase of the oxonitridosilicate chloride Ce4[Si4O3 + x N7 − x ]Cl1 − x O x , x ≃ 0.2

2006 ◽  
Vol 62 (2) ◽  
pp. 205-211 ◽  
Author(s):  
Alexandra Friedrich ◽  
Eiken Haussühl ◽  
Wolfgang Morgenroth ◽  
Alexandra Lieb ◽  
Björn Winkler ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Single Crystal ◽  
Structural Changes ◽  
Low Pressure ◽  
First Order Phase Transition ◽  
Compression Mechanism ◽  
Diamond Anvil ◽  
Structural Mechanisms ◽  
First Order Phase

The structural compression mechanism of Ce4[Si4O3 + x N7 − x ]Cl1 − x O x , x ≃ 0.2, was investigated by in situ single-crystal synchrotron X-ray diffraction at pressures of 3.0, 8.5 and 8.6 GPa using the diamond–anvil cell technique. On increasing pressure the low-pressure cubic structure first undergoes only minor structural changes. Between 8.5 and 8.6 GPa a first-order phase transition occurs, accompanied by a change of the single-crystal colour from light orange to dark red. The main structural mechanisms, leading to a volume reduction of about 5% at the phase transition, are an increase in and a rearrangement of the Ce coordination, the loss of the Ce2, Ce3 split position, and a bending of some of the inter-polyhedral Si—N—Si angles in the arrangement of the corner-sharing Si tetrahedra. The latter is responsible for the short c axis of the orthorhombic high-pressure structure compared with the cell parameter of the cubic low-pressure structure.

Bulk modulus and high-pressure crystal structures of tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 determined by X-ray powder diffraction

2000 ◽  
Vol 56 (2) ◽  
pp. 310-316 ◽  
Author(s):  
Robert E. Dinnebier ◽  
Stefan Carlson ◽  
Sander van Smaalen
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Crystal Structures ◽  
Phase Iii ◽  
Ambient Conditions ◽  
Space Group ◽  
X Ray ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase

The pressure dependence of the crystal structure of cubic tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 (TC) (P < 16.0 GPa, T = 298 K) is reported using high-resolution angle-dispersive X-ray powder diffraction. The compound has crystal structures with the molecules in a cubic-close-packed (c.c.p.) arrangement. It shows three phase transitions in the measured pressure range. At ambient conditions, TC has space group Fm{\bar 3}m (Z = 4) with a = 12.8902 (2) Å, V = 2141.8 (1) Å3 (phase I). Between 0 and 0.13 GPa TC exhibits a first-order phase transition into a structure with space group Pa{\bar 3} (phase II). A second first-order phase transition occurs between 0.2 and 0.28 GPa into a structure with space group P213 (phase III). Under non-hydrostatic pressure conditions (P > 10  GPa) a transformation is observed into a c.c.p. structure that is different from the face-centred-cubic structure at ambient conditions. A non-linear compression behaviour is observed, which could be described by a Vinet relation in the range 0.28–4.8 GPa. The extrapolated bulk modulus of the high-pressure phase III was determined to be K 0 = 7.1 (8) GPa. The crystal structures in phase III are refined against X-ray powder data measured at several pressures between 0.49 and 4.8 GPa, and the molecules are found to be fully ordered. This is interpreted to result from steric interactions between neighbouring molecules, as shown by analysing the pressure dependence of intramolecular angles, torsion angles and intermolecular distances. Except for their cell dimensions, phases I, II and III are found to be isostructural to the corresponding phases at low temperatures.

Raman study of tetragonal TbPO4and observation of a first-order phase transition at high pressure

2008 ◽  
Vol 20 (42) ◽  
pp. 425216 ◽  
Author(s):  
A Tatsi ◽  
E Stavrou ◽  
Y C Boulmetis ◽  
A G Kontos ◽  
Y S Raptis ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Order Phase Transition ◽  
First Order ◽  
First Order Phase Transition ◽  
Raman Study ◽  
First Order Phase

Order–disorder phenomena determined by high-resolution powder diffraction: the structures of tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 and tetrakis(trimethylsilyl)silane Si[Si(CH3)3]4

1999 ◽  
Vol 55 (6) ◽  
pp. 1014-1029 ◽  
Author(s):  
Robert E. Dinnebier ◽  
Wayne A. Dollase ◽  
Xavier Helluy ◽  
Jörg Kümmerlen ◽  
Angelika Sebald ◽  
...  
Keyword(s):  
Phase Transition ◽  
Low Temperature ◽  
Intermediate Phase ◽  
Lattice Parameter ◽  
Temperature Phase ◽  
Space Group ◽  
First Order ◽  
First Order Phase Transition ◽  
First Order Phase ◽  
Low Temperature Phase

The compounds tetrakis(trimethylsilyl)methane C[Si(CH3)3]4 (TC) and tetrakis(trimethylsilyl)silane Si[Si(CH3)3]4 (TSi) have crystal structures with the molecules in a cubic closed-packed (c.c.p.) stacking. At room temperature both structures have space group Fm{\bar 3}m (Z = 4) with a = 13.5218 (1) Å, V = 2472.3 (1) Å3 for TSi, and a = 12.8902 (2) Å, V = 2141.8 (1) Å3 for TC. X-ray scattering data can be described by a molecule with approximately sixfold orientational disorder, ruling out a structure with free rotating molecules. Upon cooling, TSi exhibits a first-order phase transition at T c = 225 K, as is characterized by a jump of the lattice parameter of Δa = 0.182 Å and by an exothermal maximum in differential scanning calorimetry (DSC) with ΔH = 11.7 kJ mol−1 and ΔS = 50.0 J mol−1 K−1. The structure of the low-temperature phase is refined against X-ray powder data measured at 200 K. It has space group P2 13 (Z = 4), a = 13.17158 (6) Å and V = 2285.15 (2) Å3. The molecules are found to be ordered as a result of steric interactions between neighboring molecules, as is shown by analyzing distances between atoms and by calculations of the lattice energy in dependence on the orientations of the molecules. TC has a phase transition at T c1 = 268 K, with Δa 1 = 0.065 Å, ΔH 1 = 3.63 kJ mol−1 and ΔS 1 = 13.0 J mol−1 K−1. A second first-order phase transition occurs at T c2 = 225 K, characterized by Δa 2 = 0.073 Å, ΔH 2 = 6.9 kJ mol−1 and ΔS 2 = 30.0 J mol−1 K−1. The phase transition at higher temperature has not been reported previously. New NMR experiments show a small anomaly in the temperature dependence of the peak positions in NMR to occur at T c2. Rietveld refinements were performed for the low-temperature phase measured at T = 150 K [space group P2 13, lattice parameter a = 12.609 (3) Å], and for the intermediate phase measured at T = 260 K [space group Pa{\bar 3}, lattice parameter a = 12.7876 (1) Å]. The low-temperature phase of TC is formed isostructural to the low-temperature phase of TSi. In the intermediate phase the molecules exhibit a twofold orientational disorder.

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