Structural phase change

Many metals and metallic alloys show martensitic transformations at temperatures below the melting point. Martensitic transformations are structural phase changes of first order which belong to the broader class of diffusion js solid-state phase transformations. These are structural transformations of the crystal lattice, which do not involve long-range atomic movements. A recent review of the properties and the classification of diffusionless transformations has been given by Delayed... 

Simulations of octahedral molecular clusters at constant temperature show two kinds of structural phase changes, a high-temperature discontinuous transformation analogous to a first-order bulk phase transition, and a lower-temperature continuous transformation, analogous to a second-order bulk phase transition. The former shows a band of temperatures within which the two phases coexist and hysteresis is likely to appear in cooling and heating cycles Fig. 10 the latter shows no evidence of coexistence of two phases. The width of the coexistence band depends on cluster size an empirical relation for that dependence has been inferred from the simulations. 

It would certainly be desirable to see some definitive work establishing the validity of Equation 25 in at least a few systems. The above two examples suggest, furthermore, that it may be entirely possible to have metastable films at one or the other solid interface-for example, if the liquid-film transition involves a structural phase change [11], so that nucleation may be required to produce an equilibrium film. 

Rahman Khan (1977, 1987b) explains the variation of resistivity with temperature and thickness in terms of structural phase changes. It is observed that the temperature dqiendence of the resistance and TCR values indicate metallic conduction characteristics of the hydrides. The thickness dependence of resistivity of H0H2 films (7-90 nm) at 293 and 77 K is given in fig. 13. Surplice and Kandasamy (1982), Kandasamy and Surplice (1981, 1982, 1985) have studied H-Sc, H-Er and H-Yb systems and deduced phase boundaries from changes of film resistance with atomic ratio H/R. The slow variation of... 

The CP/MAS NMR technique is also useful for investigating dynamic processes in solids such as re-orientational processes and structural phase transitions an example of solid-state phase transition monitored by variable temperature Sn CP/MAS is given by Me3Sn-C=C-C=C-SnMe3, for which a structural phase change occurs in the temperature range 232-248K. 

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