Calorimetric study of order–disorder and martensitic phase transitions in methylammonium hexachlorotellurate
- 1 February 1988
- journal article
- research article
- Published by Taylor & Francis in Philosophical Magazine A
- Vol. 57 (2) , 245-260
- https://doi.org/10.1080/01418618808204514
Abstract
Heat capacities of methylammonium hexachlorotellurate (IV), (CH3NH3)2[TeCl6], have been measured in the temperature range 13–300 K. Five phase transitions were identified, of which three are reported here for the first time. The temperatures and entropies of the transitions are as follows, 73 K (0·77 R), 137 K (1·79 R), ∼ 155 K (0·30 R), 226 K (0·20 R) and 439 K (1·18 R). Those transactions at 137 and 226 K are of higher order and the others are first order. The 155 K transition is martensitic: it can be suspended at any intermediate stage with the two phases coexisting. The 439 K transition is accompanied by an anisotropic to isotropic change of the optical property. The hysteresis around the 155 K transition explains the complicated behaviour of the substance previously reported in nuclear resonance experiments.Keywords
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