Medidas de coeficiente piroelétrico e transição de fase em LiKSO4

Abstract

In this work the LiKSO crystal was studied at ambient pressure by means of dielectrical and pyroelectrical measurements as a function of temperature in the range from 15 to 300K. The anomalies observed in the dielectric constant and coefficient pyroelectrical curves were related to three first order phase transitions. The first transition occurs at 250K on heating (201 on cooling). There is no concordance in the bibliography on the structure of the crystal below 250K. Some workers suggest a trigonal simmetry belonging to space group C43v (P31c), others propose a hexagonal structure with space group C46v(P69mc) while others suggest an intermediate phase group of the C46v kind. All this models are discuassed in this work. A second transition occurs at 190K during heating (180K during cooling). Again, there is a disagreement about the atructure and the spacial group for the phase below 190K. A different model that is better compatible with our electrical measurements is proposed. For the third transition, which occurs at 30K during heating (20K during cooling), we present a model that explain this transition and the passible simmetry group for this new phase.