On the high-temperature phase transitions of some KDP-family compounds: a structural phase transition? A transition to a bulk-high proton conducting phase?

1999 ◽  
Vol 125 (1-4) ◽  
pp. 177-185 ◽  
Author(s):  
E Ortiz ◽  
R.A Vargas ◽  
B.-E Mellander
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Conducting Phase ◽  
Proton Conducting ◽  
High Proton

A high temperature structural phase transition in crocoite (PbCrO4) at 1068 K: crystal structure refinement at 1073 K and thermal expansion tensor determination at 1000 K

2000 ◽  
Vol 64 (2) ◽  
pp. 291-300 ◽  
Author(s):  
K. S. Knight
Keyword(s):  
Crystal Structure ◽  
Phase Transition ◽  
Thermal Expansion ◽  
High Temperature ◽  
Structural Phase Transition ◽  
Structural Phase ◽  
Structure Type ◽  
Temperature Phase ◽  
Thermal Expansion Tensor ◽  
Principal Axes

AbstractHigh-resolution, neutron time-of-flight, powder diffraction data have been collected on natural crocoite between 873 and 1073 K. Thermal analysis carried out in the 1920s had suggested that chemically pure PbCrO4 exhibited two structural phase transitions, at 964 K, to the β phase, and at 1056 K, to the γ phase. In this study, no evidence was found for the α-β structural phase transition, however a high-temperature phase transition was found at ∼1068 K from the ambient-temperature monazite structure type to the baryte structure type. The phase transition, close to the temperatures reported for the β to γ phase modifications, is first order and is accompanied by a change in volume of −1.6%. The crystal structure of this phase has been refined using the Rietveld method to agreement factors of Rp = 0.018, Rwp = 0.019, Rp = 0.011. No evidence for premonitory behaviour was found in the temperature dependence of the monoclinic lattice constants rom 873 K to 1063 K and these have been used to determine the thermal expansion tensor of crocoite just below the phase transition. At 1000 K the magnitudes of the tensor coefficients are α11, 2.66(1) × 10−5 K−1; α22, 2.04(1) × 10−5 K−1; α33, 4.67(4) × 10−5 K−1; and α13, −1.80(2) × 10−5 K−1 using the IRE convention for the orientation of the tensor basis. The orientation of the principal axes of the thermal expansion tensor are very close to those reported previously for the temperature range 50–300 K.

High-temperature reversible phase transitions and exceptional dielectric anomalies in cobalt(ii) based ionic crystals: [Me3NCH2X]2[CoX4] (X = Cl and Br)

2018 ◽  
Vol 47 (17) ◽  
pp. 6218-6224 ◽  
Author(s):  
Xiu-Ni Hua ◽  
Chao-Ran Huang ◽  
Ji-Xing Gao ◽  
Yang Lu ◽  
Xiao-Gang Chen ◽  
...  
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Ionic Crystals ◽  
Temperature Phase Transition ◽  
Reversible Phase

Two isostructural cobalt(ii) based ionic crystals with exceptional dielectric anomalies have been designed as new high-temperature phase transition materials.

scholarly journals Inorganic Anion Regulates the Phase Transition in Two Organic Cation Salts Containing [(4-Nitroanilinium)(18-crown-6)]+ Supramolecules

2017 ◽  
Author(s):  
Yuan Chen ◽  
Yang Liu ◽  
Binzu Gao ◽  
Chuli Zhu ◽  
Zunqi Liu
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
Variable Temperature ◽  
Structural Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Space Group ◽  
X Ray

Two novel inorganic–organic hybrid supramolecular assemblies, namely, (4-HNA)(18-crown-6)(HSO4) (1) and (4-HNA)2(18-crown-6)2(PF6)2(CH3OH) (2) (4-HNA = 4-nitroanilinium), were synthesized and characterized by infrared spectroscopy, single X-ray diffraction, differential scanning calorimetry (DSC), and temperature-dependent dielectric measurements. The two compounds underwent reversible phase transitions at about 255 K and 265 K, respectively. These phase transitions were revealed and confirmed by the thermal anomalies in DSC measurements and abrupt dielectric anomalies during heating. The phase transition may have originated from the [(4-HNA)(18-crown-6)]+ supramolecular cation. The inorganic anions tuned the crystal packings and thus influenced the phase-transition points and types. The variable-temperature X-ray diffraction data for crystal 1 revealed the occurrence of a phase transition in the high-temperature phase with the space group of P21/c and in the low-temperature phase with the space group of P21/n. Crystal 2 exhibited the same space group P21/c at different temperatures. The results indicated that crystals 1 and 2 both underwent an iso-structural phase transition.

HIGH TEMPERATURE PHASE TRANSITIONS WITHOUT INFRARED DIVERGENCES

1994 ◽  
Vol 09 (22) ◽  
pp. 4029-4061 ◽  
Author(s):  
N. TETRADIS ◽  
C. WETTERICH
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Order Phase Transition ◽  
High Temperature Phase ◽  
Second Order ◽  
Temperature Phase ◽  
Perturbative Approach ◽  
Temperature Phase Transition ◽  
Infrared Divergences

The most commonly used method for the study of high temperature phase transitions is based on the perturbative evaluation of the temperature-dependent effective potential. This method becomes unreliable in the case of a second order or weakly first order phase transition, due to the appearance of infrared divergences. These divergences can be controlled through the method of the effective average action, which employs renormalization group ideas. We report on the study of the high temperature phase transition for the N-component ϕ4 theory. A detailed quantitative picture of the second order phase transition is presented, including the critical exponents for the behavior in the vicinity of the critical temperature. An independent check of the results is obtained in the large N limit, and contact with the perturbative approach is established through the study of the Schwinger–Dyson equations.

TEM of Phase Transitions in Tridymite and Cristobalite Based Materials.

2000 ◽  
Vol 6 (S2) ◽  
pp. 358-359
Author(s):  
Gustaaf Van Tendeloo
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Solid State ◽  
Wide Temperature Range ◽  
Room Temperature ◽  
Paraelectric Phase ◽  
High Temperature Phase ◽  
Temperature Phase ◽  
Extended Defects

We have determined the structure of the paraelectric phase of BaAl2O4, which is a stuffed tridymite, by different TEM techniques and we will describe the phase transition between the ferroelectric room temperature phase and the paraelectric high temperature phase. We have also obtained HREM images of the higly radiation sensitive acristobalite phase of (Si0,9 Ge0,1)O2 and analysed the extended defects in this material.The stuffed tridymite BaAl2O4 is ferroelectric at room temperature and undergoes a paraelectric-ferroelectric (PEFE) phase transition. The transition is reversible, takes place over a wide temperature range (400K-670K) and has a dynamical character. BaAl2O4 is easily obtained by solid state reaction of BaCO3, and A12O4,. The stoichiometric amounts of the initial reagents were mixed, grinded in an agate mortar under acetone and pressed into a pellet. The pellet was annealed in alumina crucibles at 1000 °C and 1300 °C for 40 h in air and furnace cooled.

Reversible high-temperature phase transition of a manganese(II) formate framework with imidazolium cations

2013 ◽  
Vol 69 (6) ◽  
pp. 616-619 ◽  
Author(s):  
Bi-Qin Wang ◽  
Hai-Biao Yan ◽  
Zheng-Qing Huang ◽  
Zhi Zhang
Keyword(s):  
Phase Transition ◽  
High Temperature ◽  
Low Temperature ◽  
Variable Temperature ◽  
Structural Phase ◽  
High Temperature Phase ◽  
Mirror Plane ◽  
Temperature Phase ◽  
Temperature Structure ◽  
Imidazolium Cations

A new metal–formate framework, poly[1H-imidazol-3-ium [tri-μ2-formato-manganese(II)]], {(C3H5N2)[Mn(HCOO)3]}n, was synthesized and its structural phase transition was studied by thermal analysis and variable-temperature X-ray diffraction analysis. The transition temperature is around 435 K. The high-temperature phase is tetragonal and the low-temperature phase is monoclinic, with a β angle close to 90°. The relationship of the unit cells between the two phases can be described as:aHT= 0.5aLT+ 0.5bLT;bHT= −0.5aLT+ 0.5bLT;cHT = 0.5cLT. In the high-temperature phase, both the framework and the guest 1H-imidazol-3-ium (HIm) cations are disordered; the HIm cations are located about 2mmsites and were modelled as fourfold disordered. The Mn and a formate C atom are located on fourfold rotary inversion axes, while another formate C atom is on a mirror plane. The low-temperature structure is ordered and consists of two crystallographically independent HIm cations and two crystallographically independent Mn2+ions. The phase transition is attributable to the order–disorder transition of the HIm cations.

Reconstructive phase transition in (NH4)3TiF7accompanied by the ordering of TiF6octahedra

2014 ◽  
Vol 70 (6) ◽  
pp. 924-931 ◽  
Author(s):  
Maxim Molokeev ◽  
S. V. Misjul ◽  
I. N. Flerov ◽  
N. M. Laptash
Keyword(s):  
Phase Transition ◽  
Phase Transitions ◽  
High Temperature ◽  
Room Temperature ◽  
Parent Phase ◽  
High Temperature Phase ◽  
Cubic Phase ◽  
Temperature Phase ◽  
Large Rotations ◽  
Fourfold Axis

An unusual phase transitionP4/mnc→ Pa\bar 3 has been detected after cooling the (NH4)3TiF7compound. Some TiF6octahedra, which are disordered in the room-temperature tetragonal structure, become ordered in the low-temperature cubic phase due to the disappearance of the fourfold axis. Other TiF6octahedra undergo large rotations resulting in huge displacements of the F atoms by 1.5–1.8 Å that implies a reconstructive phase transition. It was supposed that phasesP4/mbmand Pm\bar 3m could be a high-temperature phase and a parent phase, respectively, in (NH4)3TiF7. Therefore, the sequence of phase transitions can be written as Pm\bar 3m →P4/mbm→P4/mnc→ Pa\bar 3. The interrelation between (NH4)3TiF7, (NH4)3GeF7and (NH4)3PbF7is found, which allows us to suppose phase transitions in relative compounds.

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