Pressure-temperature-induced transition

Pressure-temperature-induced transition to the cubic, deficient ThjP -type structure for rare earth sesquisulfides and sesquiselenides, determined on quenched samples by Eatough et al. (1969) and Eatough and Hall (1970). The selenide phases were prepared from stoichiometric mixtures of the components. 

Pressure-temperature-induced transition to the orthorhombic U2Sj-type structure for rare earth sesijuisulfides, determined on quenched samples by Range and Leeb (1975). 

Hiickel calculations have been employed extensively in other approaches such as the angular overlap model and the method of moments developed by Burdett and coworkers. Stabilities of crystal structures, pressure- and temperature-induced transitions, dynamical pathways in reactions and other phenomena have been analysed using angular overlap models. Thus, the electronic control of rutile structures and the stability of the defect structure of NbO have been examined (Burdett, 1985 Burdett Mitchell, 1993). In the case of NbO, the structure is stable at involving the formation... 

Melnichenko, Y. B. Kiran, E. Wignall, G. D. Heath, K. D. Salaniwal, S. Cochran, H. D. Stamm, M. Pressure- and Temperature-Induced Transitions in Solutions of Poly(dimethylsiloxane) in Supercritical Carbon Dioxide. Macromolecules 1999, 32, 5344—5347. 

Y. B. Melnichenko, E. Kiran, G. D. Wignall, K. D. Heath, S. Salaniwal, H. D. Cochran, and M. Stamm, Pressure- and temperature-induced transitions in solutions ofpoly(dimethyl siloxane) in supercritical carbon dioxide, A/acro/Mofecwfei 32 5344 (1999). 

Figure 8. Left panel phase diagram of ice T> T (P)) and transition lines corresponding to the ice Ih-to-HDA, LDA-to-HDA, and HDA-to-LDA transformations T

Pressure-temperature-induced structural transitions for rare earth tri-aluminides, determined on quenched samples by Cannon and Hall... 

The temperature-induced transition from> rhombohedral (R-3m) LaOF, SmOF, GdOF, and ErOF to the fluorite type shifts to higher temperatures with increasing pressure (studied up to 4 GPa by DTA (Pistorius 1973)). The oxyfluorides LnOF of La, Pr, Nd, Sm, Eu, and Gd transforms to the PbClj type around 1270K under pressures of 4 to 9 GPa, with a volume decrease of about 6.5% (Gondrand et al. 1970) (quenched samples). Rhombohedral YOF did not show a phase transformation under these conditions, rhombohedral TbOF and DyOF became tetragonal. 

The conversion of lipid/water systems from one type of phase to another can be induced by physical and chemical parameters. The phase structure depends, for instance, on the water content of the sample, but also on temperature and pressure. For systems with more than one lipid component, the lipid composition is, of course, also important. The phase transformation can be easily studied by differential scaruiing calorimetry (DSC) for a temperature induced transition, and... 

Pressure-induced phase transitions in the titanium dioxide system provide an understanding of crystal structure and mineral stability in planets interior and thus are of major geophysical interest. Moderate pressures transform either of the three stable polymorphs into the a-Pb02 (columbite)-type structure, while further pressure increase creates the monoclinic baddeleyite-type structure. Recent high-pressure studies indicate that columbite can be formed only within a limited range of pressures/temperatures, although it is a metastable phase that can be preserved unchanged for years after pressure release Combined Raman spectroscopy and X-ray diffraction studies 6-8,10 ave established that rutile transforms to columbite structure at 10 GPa, while anatase and brookite transform to columbite at approximately 4-5 GPa. 

The calculated Aa values of pure DPPC bilayers are plotted as a function of pressure in Fig. 18. Only the absolute value of Aa can be determined from Eq. (7), but in view of the fact that Aa is negative for the LC phase and the temperature-induced gel phases (GI, GII), it is expected that Aa will also be negative for the high pressure gel phases of DPPC. The absolute value of Aa increases slightly with pressure in the LC phase in the pressure range from 1 to 500 bar. The transition from the LC phase to the GI phase is accompanied by a... 

The peak height ratio between the antisymmetric and symmetric CHj stretching modes H-2880/H-2850 is plotted as a function of pressure in Figure 7. This parameter has been shown to reflect the magnitude of interchain interactions in systems that contain polymethylene chains [20]. An abrupt increase in this ratio, and thus an increase in the interchain interactions, is observed at the pressure-induced transition from the micellar to the coagel phase. Furthermore, it is also evident from Figure 7 that the transition has a considerable pressure hysteresis. Interestingly, pressure [76] and temperature [79] have different effects on the H-2880/H-2850 ratio in the micellar phase of... 

The line shifts of f-f transitions discussed in sect. 4.2, offer an interesting possibility to establish high pressure gauges. As mentioned in sect. 2, ruby is still the most widely used gauge for pressure determination. However, some deficiencies caused a continuous search for improved sensor materials. Especially the temperature induced broadening and quenching limits the application of ruby to below 500 °C. 

Another luminescence sensor, SrlLOyiSm2"1" has been suggested by Lacam and Chateau (1989). The advantage of using Sm2+ instead of Sm3+ is the occurrence of the well-isolated singlet transition 5Do -> 7Fo at 685.41 nm at ambient conditions. Also in this case the pressure-induced shift was similar to ruby, whereas the temperature-induced shift was much smaller. The stability of the host was proven up to 108 GPa (Leger et al., 1990) and the shift of the 5Do -> 7Fo transition has been calibrated in a hydrostatic medium (helium) up to 124 GPa (Datchi et al., 1997). 

The concept of a single structural transition in amorphous material, i.e., an amorphous-amorphous transition, was coined in 1985 by Mishima et al. [25] on the example of water. Today, in many respects the nature of pressure- and/or temperature-induced transformations in glasses and amorphous solids remains unclear. In most cases, the pressure treatment of glasses and amorphous solids results in residual densification. In the process, the densified glasses and... 

It is evident that similar sets of multiple-phase transitions are bound to be observed in the respective melts. Such structural studies on the oxide melts have not yet been carried out, which is because of greater experiment complexity. Nevertheless, the chalcogenide melts, which experience structural transformations at more moderate temperatures and pressures, give examples of multiple phase transitions. Thus, the AsS [29] and CdTe [130] melts feature at least two pressure-induced transitions accompanied by a change in the short-range order structure and properties of the liquids. 

The metal-insulator transition induced by hydrogen causes also changes of the electric resistance of the sample. The physical relation is rather complicated as it depends on the electronic changes as well as hydride growth mechanism and morphology. Therefore, in most cases, the change in resistance behavior is used to determine the onset of hydride formation/ decomposition. Repeating the measurements at various applied pressures/temperatures reveals a van t Hoff plot, similar to DSC-measurements (2.3). 

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