ETCH RATE OF GADOLINIUM GALLIUM GARNET IN CONCENTRATED PHOSPHORIC-ACID OF VARYING COMPOSITION

The etch rate of Gd//3Ga//5O//1//2 in concentrated phosphoric acid betweeen 140 and 180 C was found to vary directly with the square of the H//3PO//4 concentration when dilution of the H//3PO//4 with higher acids occurs as a result of dehydration. When the H//3PO//4 concentration is reduced by dilution with water, however, the etch rate continues to increase reaching a maximum value at a dilution of approximately 50 mole percent (m/o) H//2O at 140 C. For any given acid composition the etch rate varies exponentially with temperature.