A New Approach of the -OH Content in Berlinite Crystals

Abstract In view of the numerous methods, often inconsistent, proposed to quantify the OH content from IR measurements in the piezoelectric materials as quartz and MX O 4 ( M = Al, Ga and X = P, As) quartz-like crystals, we have reinvestigated this determination. This knowledge is very important, because it is closely related to piezoelectric properties, in particular the Q factor, which is drastically reduced by this impurity. After a brief overview of previous studies devoted to quartz and berlinite crystals, we develop a formula taking into consideration an anisotropic factor, γ for the OH content distribution. This relation has been applied to IR measurements of a berlinite bar. Then, the C OH content can be directly estimated from the height, K , of the 3300 cm -1 absorption band: C OH/(Al+P) ppm = 907 K with an isotropic OH distribution.