Iodine NQR and Phase Transitions in [N(CH3)4]2 ZnI4

1990 ◽  
Vol 45 (3-4) ◽  
pp. 349-352 ◽  
Author(s):  
J. Pirnat ◽  
J. Lužnik ◽  
Z. Trontelj
Keyword(s):  
Crystal Structure ◽  
Phase Transitions ◽  
High Temperature ◽  
Temperature Dependence ◽  
General Formula ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Space Group ◽  
Crystal Space ◽  
Group D

Abstract Using a superregenerative NQR spectrometer, the temperature dependence of 127I NQR spectra in [N(CH3)4]2ZnI4 was measured between 167 and 335 K. The measurements confirm two known structural phase transitions at 219 and 257.5 K. The correspondence between the distinct regions of iodine NQR spectra and the crystal structure is discussed. The relation of [N(CH3)4]2ZnI4 to the incommensurate family with the general formula X2YZ4 and the high temperature (paraphase) crystal space group D162h (Pmcn) is studied.

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.

scholarly journals Structural and optical study of the phase transitions in Lead Hafnate, PbHfO3

2014 ◽  
Vol 70 (a1) ◽  
pp. C58-C58
Author(s):  
Steven Huband ◽  
Anthony Glazer ◽  
Krystian Roleder ◽  
Andrzej Majchrowski ◽  
Pam Thomas
Keyword(s):  
Phase Transitions ◽  
Structural Phase ◽  
Orthorhombic Phase ◽  
Temperature Hysteresis ◽  
Structural Phase Transitions ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Fundamental Understanding ◽  
Distinct Temperature

Lead Hafnate undergoes two structural phase transitions as a function of temperature. The first occurs at about 1630C, consisting of a transition from an antiferroelectric orthorhombic Pbam structure [1] to another antiferroelectric orthorhombic phase with an as-yet undetermined space group. The second is to a paraelectric cubic Pm3m structure at 2090C. Dielectric spectroscopy measurements on a single crystal have shown a distinct temperature hysteresis at the orthorhombic to orthorhombic transition [2]. Recently, dielectric measurements on a ceramic sample have shown a much larger temperature hysteresis and following x-ray diffraction measurements, it is suggested that the second orthorhombic phase is in space group A2mm and undergoes another transition to a tetragonal P4mm structure before the cubic transition [3]. We report on the results of an investigation of a PbHfO3crystal using a combination of high-resolution x-ray diffraction and birefringence imaging measurements with the Metripol system. These measurements have been performed as a function of temperature from the room-temperature orthorhombic structure to the high-temperature cubic structure. The results are discussed both in the context of the published work and fundamental understanding of the origin of antiferroelectricity.

Structural phase transitions at high-temperature in double perovskite Sr2GdRuO6

2012 ◽  
Vol 407 (16) ◽  
pp. 3150-3154 ◽  
Author(s):  
C.A. Triana ◽  
L.T. Corredor ◽  
D.A. Landínez Téllez ◽  
J. Roa-Rojas
Keyword(s):  
Phase Transitions ◽  
High Temperature ◽  
Structural Phase ◽  
Double Perovskite ◽  
Structural Phase Transitions

scholarly journals NQR and DSC Studies on Structural Phase Transitions and Lattice Stability in Some Tetrabromozincate(II) Compounds A2ZnBr4

2002 ◽  
Vol 57 (6-7) ◽  
pp. 425-430 ◽  
Author(s):  
Keizo Horiuchi ◽  
Hideta Ishihara ◽  
Naoko Hatano ◽  
Syuntaroh Okamoto ◽  
Tohru Gushiken
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Temperature Dependence ◽  
Single Phase ◽  
Structural Phase ◽  
Lattice Stability ◽  
Structural Phase Transitions ◽  
Melting Points ◽  
Dsc Studies ◽  
Disorder Type

The temperature dependence of 81Br NQR frequencies in some tetrabromozincate(II) compounds, pyridinium tetrabromozincate(II) (pyH)2ZnBr4, 4-picolinium tetrabromozincate(II) (4- piH)2ZnBr4, 2,6-lutidinium tetrabromozincate(II) (2,6-luH)2ZnBr4 and guanidinium tetrabromozincate( II) (guH)2ZnBr4,weremeasured between 77Kand temperatureswhere signals faded out.All compounds exhibited four NQR signals over the whole temperature range investigated. Moreover, DSC was measured between about 130 K and melting points. (4-piH)2ZnBr4 and (guH)2ZnBr4 showed no structural phase transition, while (pyH)2ZnBr4 and (2,6-luH)2ZnBr4 showed a single phase transition. The values of transition entropies obtained suggest that these transitions are of the order-disorder type. The nature of these transitions and the lattice stability in the present compounds were discussed

Hochtemperatursynthese und Kristallchemie der Oxotantalate Cr2+0,761Ta2,095O6 und FeTa2O6 / High Temperature Synthesis and Crystal Chemistry of the Oxotantalates Cr2+0,761Ta2,095O6 and FeTa2O6

1995 ◽  
Vol 50 (5) ◽  
pp. 712-716 ◽  
Author(s):  
E. Peters ◽  
Hk. Müller-Buschbaum
Keyword(s):  
Crystal Structure ◽  
High Temperature ◽  
Monoclinic Symmetry ◽  
Temperature Synthesis ◽  
Space Group ◽  
High Temperature Synthesis ◽  
Laser Techniques ◽  
Group D ◽  
Symmetry Space ◽  
Symmetry Space Group

Abstract Black single crystals of Cr0.761Ta2.095O6 have been prepared by CO2-LASER techniques. This phase crystallizes with monoclinic symmetry, space group C52h-P21/c, a = 4.748(1). b = 4.750(2), c = 10.405(3) Å, β = 117.152(13)°, Z = 2. The crystal structure is closely related to the trirutile type, although the metal positions are partly statistically occupied by Cr2+ and Ta5+ or underoccupied by Ta5+, respectively. FeTa2O6, prepared by the same m ethod does neither show any statistic occupation nor deviations from the trirutile structure, space group D144h-P42/mnm, a = 4.7595(5) Å, c = 9.201(2)A, Z = 2 .

scholarly journals Crystal structure and structural phase transitions in the GdBaCo2O5.0cobaltite

2011 ◽  
Vol 84 (10) ◽  
Author(s):  
Leonardo Lo Presti ◽  
Mattia Allieta ◽  
Marco Scavini ◽  
Paolo Ghigna ◽  
Laura Loconte ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Phase Transitions ◽  
Structural Phase ◽  
Structural Phase Transitions

Evidence for precursor clusters associated with structural phase transitions in antifluorite crystals

1982 ◽  
Vol 60 (4) ◽  
pp. 397-398 ◽  
Author(s):  
Robin L. Armstrong ◽  
Marie D'Iorio ◽  
Maximo E. Ramia
Keyword(s):  
Phase Transitions ◽  
Temperature Dependence ◽  
Structural Phase ◽  
Indirect Evidence ◽  
Cubic Phase ◽  
Structural Phase Transitions ◽  
Type Phase ◽  
Symmetry Phase ◽  
Nuclear Quadrupole ◽  
Low Symmetry

Measurements of the temperature dependence of the intensities of the halogen nuclear quadrupole resonances in K2PtBr6 and K2ReCl6, in the cubic phase are reported. These results provide indirect evidence for the formation of dynamic clusters of the low symmetry phase as a precursor to the occurrence of rotative type phase transitions to tetragonal structures in these crystals.

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