Thermal expansion and spontaneous strain of KMnF3 near the 186 K-structural phase transition |
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| Authors: | H. Sakashita N. Ohama A. Okazaki |
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| Affiliation: | 1. The Centre of Advanced Instrumental Analysis, Kyushu University , Kasuga, 816, Japan;2. Department of Literature , Seinan Gakuin University , Fukuoka, 814, Japan;3. Department of Physics , Kyushu University , Fukuoka, 812, Japan |
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| Abstract: | Abstract By means of high-angle double-crystal X-ray diffractometry (HADOX), the thermal expansivity of KMnF3 has been determined. The linear thermal expansion coefficient along each crystallographic axis exhibits a divergent anomaly at the structural phase transition at 186 K. The critical exponents of these coefficients are determined: in the cubic phase α = 0.21 ± 3, and in the tetragonal phase α′ = 0.19 ± 3 for the a axis and α″ = 0.35 ± 3 for the c axis. In addition, the critical exponent of the spontaneous strain, c/a ? 1, is determined to be 0.4248 ± 8, which is smaller than that of the order parameter 2β = 0.5714 ± 12. These values are reasonable if the transition occurs in the vicinity of a tricritical point. |
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| Keywords: | X-ray diffraction lattice constant phase transition critical exponent potassium manganese fluoride. |
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