Strontium titanate SrTiO 3 (100), (110), and (111) single crystals, undoped or donor doped with up to 1 at% La, were isothermally equilibrated at temperatures between 1523 and 1773 K in synthetic air followed by two different methods of Sr tracer deposition: ion implantation of 87 Sr and chemical solution deposition of a thin 86 SrTiO 3 layer. Subsequently, the samples were diffusion annealed under the same conditions as before. The initial and final depth profiles were measured by SIMS. For strong La-doping both tracer deposition methods yield similar Sr diffusion coefficients, whereas for weak doping the tracer seems to be immobile in the case of ion implantation. The Sr diffusivity does not depend on the crystal orientation, but shows strong dependency on the dopant concentration supporting the defect chemical model that under oxidizing conditions the donor is compensated by Sr vacancies. A comparison with literature data on Sr vacancy, Ti, and La diffusion in this system confirms the concept that all cations move via Sr vacancies. Cation diffusion is several orders of magnitude slower than oxygen diffusion.

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Measurements of the temperature dependence of surface acoustic wave velocity were performed for propagation on X, Y, A C, AT, and along the x axis of several other rotated Y cuts of quartz over the temperature range -25° to +75°C. A pulsed rf technique was employed. To facilitate the measurement of angular dependence of the temperature coefficient of velocity, surface wave delay lines were constructed in which the waves were excited on the quartz by means of an interdigital electrode structure on a glass substrate which was brought into contact with the quartz. Calculations of the temperature coefficients of velocity and delay time were performed using an iterative computer program based on the work of Coquin and Tiersten. The measurements and calculations are in good agreement in most cases, the largest discrepancy being approximately five percent. It is concluded that the orientation which best combines lowtemperature dependence of delay time, high coupling constant, and a minimum of deleterious side effects is 42!0 rotated V-cut quartz with propagation along the x axis.

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Langasite and gallium phosphate are shown to exhibit piezoelectrically stimulated bulk acoustic waves up to at least 1,400 and 900°C, respectively. Most critical issues are stoichiometry changes due to, e.g. low oxygen partial pressures, and high losses. Therefore, the paper discusses the atomistic transport and defect chemistry of those crystals and correlates them with the electromechanical properties. First, the defect chemistry of langasite is investigated. As long as the atmosphere is nearly hydrogen-free, the transport of charge carriers is governed by oxygen movement. A dominant role of hydrogen is observed in hydrogenous atmospheres. Based on the developed defect model, donors are expected to suppress the oxygen vacancy concentration and, thereby, the loss in langasite. The prediction is proven by niobium doping and found to be valid. A one-dimensional physical model of thickness shear mode resonators is summarized. The analysis of the resonance spectra showed that the loss of the resonators can be described satisfactorily by mechanical and electrical contributions expressed as effective viscosity and bulk conductivity, respectively. The mechanical loss in langasite is significantly impacted by the electrical conductivity due to the piezoelectric coupling. The effect of the piezoelectric coupling on the loss is negligible for gallium phosphate since it shows an extremely low electrical conductivity.

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