ETCHING KINETICS OF FLUX GROWN RARE EARTH ALUMINATE CRYSTALS. Krishen Bamzai, K. K. Sharma, P. N. Kotru, Department of Physics, University of Jammu, Jammu-India, B. M. Wanklyn, Clarendon Laboratory, University of Oxford, Oxford UK

Results of experiments performed on etching of (110) and (001) surfaces of flux grown rare earth aluminate crystals (where R = Er, Dy, Gd, Tb) using H₃PO₄ and HNO3 as etchants are described and discussed. The etching kinetics were investigated using different concentrations of the same acid as well as different proportions of two combined acids and temperatures of the etchants. The lateral and vertical etch rates are worked out and their variations with temperature are recorded. From the data, the activation energies of rare earth aluminate for lateral extension (E_L ) and depth of etch pits (E_D) are estimated. The optimum conditions of etching leading to well defined etch pits are found to be H₃PO₄ at 180deg.C keeping the etching time 10 minutes and H₃PO₄ : HNO₃ (1:1) at 150deg.C for 15 minutes. Results of experiments suggesting the formation of the point bottomed etch pits at the dislocation lines intersecting the crystal surfaces are described and discussed.