Elastic properties of 5-mol % MgO doped LiNbO3 crystals measured by line focus beam acoustic microscopy

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Abstract
An ultrasonic method of line focus beam (LFB) acoustic microscopy is applied to quantitative characterization of LiNbO3 wafers destined for optical use. Commercial Z‐cut wafers obtained from two optical grade LiNbO3 crystals, with and without 5‐mol % MgO doping, are evaluated by measuring the leaky surface acoustic wave (LSAW) velocities. Doping of 5‐mol % MgO to LiNbO3 results in an increase of about 1% in the LSAW velocities and in a decrease of about 0.1% in density. Fewer elastic inhomogeneities are observed in the undoped wafer than in the MgO doped wafer. The measured LSAW velocities are compared with the chemical and physical properties, chemical composition, density, lattice constant, refractive index, and Curie temperature. It is shown that the LFB system has a much greater sensitivity and resolution in the determination of these properties than do other analytical methods. It is suggested that this method should be adopted as a new analytical technique for establishment of the crystal growth conditions and for evaluation of optical grade LiNbO3 wafers.