Hardness and dielectric characteristics of flux grown terbium aluminate crystals

Results of indentation induced Vickers hardness testing and dielectric studies conducted on flux-grown terbium aluminate crystals are presented. It is shown that the Vickers hardness value (Hv) is independent of indentation time, but depends on the applied load. Applying the concept of Hays and Kendall, the load independent values are estimated for (110) and (001) planes. Differential behaviour in the crack formation of two different planes (110) and (001) is observed, while (001) plane develops Palmqvist cracks in the whole load range of 10–100 g, (110) plane shows a transition from Palmqvist to median cracks at 70 g. The fracture toughness, brittleness index and yield strength are determined for both the planes. The hardness anisotropy is reported. The dielectric constant, dielectric loss and conductivity are shown to be dependent on temperature and frequency of the applied a.c. field. The dielectric constant versus temperature shows a transition peak at 230°C, which remains independent of the frequency of the applied a.c. field in the range 1 kHz–13 MHz.