Phase transition in K2Cd2(SO4)3: Order parameter and microscopic distortions |
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| Authors: | Dorian M Hatch Johanne I Artman Juliana Boerio-Goates |
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| Institution: | 1. Department of Physics, Brigham Young University, 84602, Provo, UT, USA
2. Department of Chemistry, Brigham Young University, 84602, Provo, UT, USA
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| Abstract: | The transition from P213(T
4) to P212121(D
2
4
) in the langbeinite K2Cd2(SO4)3 has been analyzed using group theoretical methods and previously published structural data above and below the transition. We find that because the transition is strongly first-order, the primary-order parameter has relatively large values at the transition temperature, and higher order terms which involve the order parameter, the strain, and the coupling of the two must be included in the Landau expansion for the free energy. Complex displacements occur at the transition for all atoms of the unit cell, but these displacements can be resolved into contributions which can be shown from symmetry considerations to transform as the 
2
3 irrep of P2
1 3(T
4) as well as contributions from symmetry-preserving displacements which transform under the irrep
1. Therefore, the transition is not a simple one and involves sulfate rotations and cadmium and potassium ion displacements. |
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| Keywords: | |
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