P phase transition

An alloy is said to be of Type II if neither the AC nor the BC component has the structure a as its stable crystal form at the temperature range T]. Instead, another phase (P) is stable at T, whereas the a-phase does exist in the phase diagram of the constituents at some different temperature range. It then appears that the alloy environment stabilizes the high-temperature phase of the constituent binary systems. Type II alloys exhibit a a P phase transition at some critical composition Xc, which generally depends on the preparation conditions and temperature. Correspondingly, the alloy properties (e.g., lattice constant, band gaps) often show a derivative discontinuity at Xc. 

Deluca, P. P. Phase transitions in frozen antibiotic solutions, p. 87 bis 92, International Institute of Refrigeration (Comm. Cl, Tokyo, 1985)... 

Na3Hg, as a typical example of the first group, exhibits Pauli paramagnetism (/mol 3 x 10-5) at higher temperatures with a weak but significant temperature dependence [4], In particular the a/p phase transition for Na3Hg at 309 K is reflected in a x change of about 5%. 

We can write Clapeyron s equation in a more compact notation by letting phase transition (i.e., the constraint of remaining on the coexistence curve of a, phases)... 

Because RUMs are low-energy deformations of a framework structure, they are natural candidates for soft modes associated with displacive phase transitions (Dove 1997a,b, Dove et al. 1992, 1993, 1995, Hammonds et al. 1996). Indeed, we started by noting that the soft mode that gives the displacive a-P phase transition in quartz is a RUM, and we summarised the model by which the existence of a line of RUMs gives rise to the intermediate incommensurate phase transition. We have used the RUM analysis to explain the displacive phase transitions in a number of silicates (Dove et al. 1995, Hammonds et al. 1996). 

Brace AD, Cowley RA (1980). Stractnral Phase Transitions. Taylor Francis, London Cai Y, Thorpe MF (1989) Floppy modes in network glasses. Phys Rev B 40 10535-10542 Carpenter MA, Salje EKH, Graeme-Batber A, Wrack B, Dove MT, Knight KS (1998) Cahbration of excess thermodynamic properties and elastic corrstant variatiorts dne to the a-p phase transition in quartz. Am Mineral 83 2-22... 

Schmahl WW, Swainson IP, Dove MT, Graeme-Barber A (1992) Landau free energy and order parameter behavior of the a-p phase transition in ciistobalite. Z Kristallogr 201 125-145 Sollich P, Heine V, Dove MT (1994) The Ginzburg interval in soft mode phase transitions Consequences of the Rigid Unit Mode picture. JPhys Condensed Matter6 3171-3196 Strauch D, Domer B (1993) Lattice dynamics of a-quartz. 1. Experiment. J Phys Condensed Matter 5 6149-6154... 

Tucker MG, Dove MT, Keen DA (2000) A detailed structural characterisation of quartz on heating through the a-p phase transition. Phys Rev B (submitted)... 

Van Tendeloo G, Van Landuyt J, Amelinckx S (1976) The a-p phase transition in quartz and AIPO4 as studied by electron microscopy and diffraction. Phys Status Sohdi 33 723-735 ... 

Hatch DM, Ghose S (1991) The a-p phase transition in cristobalite, Si02 cristobalite symmetry analysis, domain stracture and transition dynamics. Phys Chem Minerals 21 67-77 Hatch DM, Ghose S, Bjorkstam JL (1994) The a-p phase transition in AIPO4. Phys Chem Minerals... 

For calibration, the temperature at the sample location can be determined by visually observing the melting of salts of known melting temperatures. The salts that have proved to be most reliable for this purpose are NaCl (800.5 °C) and NaNOs (306.8 °C). The a-P phase transition in quartz (574°C) can be used as well. The laser interferometry method described above can be used to accurately pinpoint the transition in an optically perfect platelet of quartz. 

Several published equations of state for H2O were available when the first HDAC was made. Of these, Haar et al. [10] and Saul and Wagner [11] were considered to be the most comprehensive and accurate. One of the first applications of the HDAC [5] was undertaken to compare EOS data of water with the published a-P phase transition boundary in quartz... 

The crystal structures of a-Na2Cr207 and K2Cr207 have been refined and the a- to P-phase transition in the former was discussed. A detailed study of the i.r. and Raman spectra of K2Cr207 as single crystals(77 K), as a melt (708 K), and in saturated aqueous solutions (298— 542 K) has been accomplished, and a normal-co-ordinate analysis of the dichromate ion presented in support of the proposed assignment of these experimental data. The vibrational spectra of each of the salts M2Cr207(M = K, Rb, or Cs) are unique to the extent that unambiguous identification of both the compound and its crystal form is possible. 

In the steels considered, the phase transformation proceeds in different ways. In the 18Cr-8Ni-0.03C steel, a rapid y-phase to a stable a-phase transition occurs the e-phase (h.c.p.) is not observed. In the 18Cr-10Ni-Ti steel, the h.c.p. phase transition is possible, provided that the external stress is 0.8 to 0.9cro.2 at room... 

The most important problem associated with the use of pure palladium membranes is the hydrogen embrittlement phenomenon. When the temperature is below 300 °C and the pressure below 2.0 MPa, the 3-hydride phase may nucleate from the a-phase, resulting in severe lattice strains (see Figure 13.3), so that a pure palladium membrane becomes brittle after a few cycles of oc (3 transitions. Such a problem can be overcome by using Pd-alloy containing another metal, such as silver. The palladium alloys have a reduced critical temperature for the oc-P phase transition. Pd-Ag membranes can operate in hydrogen atmosphere at temperatures below 300 °C without observing... 

The LAMOX family of oxide ion conductors, based initially on the La Mo O parent compound, are competitive with existing electrolytes at temperatures above 600 °C at which point there is an a-P phase transition (Lacorre et al. 2000). Associated with this transition is a dramatic improvement in the... 

The potential of ROFTIR has been exploited in a wide variety of polymer systems. These include the orientation processes during elongation and relaxation of polyethylene [299-301, 312] uniaxial deformation phenomena in polypropylene [302, 303, 309-311], PET [304, 305] and polystyrene [306] hard and soft segmental orientations during stretching of polyurethanes [307, 308] and the stress-induced reversible a-P phase transition in crystalline PBT [312-314] and uniaxial deformation of amorphous PBT [315]. 

Fig. 103. Discontinuity of the hexagonal c-axis of In2Se3 at the a-p phase transition [456].

R Phase transitions Refs. P Phase transitions Refs. 

D. Yairg and E L. Thomas, Effect of PMMA on the morphology and a- p phase transition of oriented PVDF/PMMA blends, J. Mat. Sei. Leo. 6 593 (1967X... 

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