An apparent Landau-type second order transition in the spinel CdIn2S4 |
| |
Authors: | W Czaja |
| |
Institution: | 1. Laboratories RCA Ltd., Hardturmstra?e 169, CH-8005, Zürich, Switzerland
|
| |
Abstract: | Experimental evidence is given of a second order transition in the spinel CdIn2S4. The specific heatc p shows a step at the transition temperature (T c=403°K), the thermal expansion coefficientα remains unaffected. An analysis yields a critical region of this transition considerably narrower (5°K) than expected from the critical regions of transitions of a similar type (quartz: 160°K,β-brass: 250°K) and therefore the critical region has not been observed experimentally, i.e. the transition appears to follow Landau’s theory. Landau’s group theoretical analysis of second order transitions in crystals leads to a model for the transition in CdIn2S4 on the atomic scale. If the temperature is decreased below the critical temperature a 1:1 ordering occurs between Cd and In on the tetrahedral sites. With this model the gross features of this transition can be qualitatively understood: The unaffected thermal expansion and the long relaxation times for the establishment of equilibrium approachingT c. Also the narrow critical region can be explained in terms of a large correlation length in CdIn2S4. Finally it is shown that a generalized formulation of the thermodynamic part of Landau’s theory correlates thermodynamic quantities far above and far below the critical temperature, as illustrated for CdIn2S4. This generalization allows also a more satisfactory determination of the critical region. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|