| Autor: |
Dvořák, V., Quilichini, M., Le Calvé, N., Pasquier, B., Heger, G., Schweiss, P., Dvořák, V., Quilichini, M., Le Calvé, N., Pasquier, B., Heger, G., Schweiss, P. |
| Zdroj: |
Journal de Physique I; October 1991, Vol. 1 Issue: 10 p1481-1498, 18p |
| Abstrakt: |
We propose a hypothetical prototype phase (space group Imm) from which all observed phases in NH4HSeO4and ND4DSeO4can be deduced by introducing order parameters of definite symmetries. Following this hypothesis the symmetry of the superionic phase should be P2/n in disagreement with recent experimental results. Free energies of Landau type are derived by means of which particular phase transitions could be described. The large dielectric anomaly near 252 K in NH4HSeO4is discussed in some detail. The first order phase transition in ND4DSeO4from the room temperature phase P212121into commensurate lock-in phase (with the wave-vector kz(0,0, π/c)) has been investigated by neutron elastic scattering and the symmetry of the latter has been found to be P1121in agreement with our theoretical prediction. |
| Databáze: |
Supplemental Index |
| Externí odkaz: |
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