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2. Bragg, W.L.: Acta Crystallogr. 1 (1948) 46.
3. Mason, W.P.: Piezoelectric Crystals and Their Applications to Ultrasonics, Princeton: D.Van Nostrand Co., 1950.
4. Bleaney, B., Stevens, K.W.H.: Paramagnetic Resonance, Rep. Prog. Phys. 16 (1953) 108.
5. von Hippel, A.R. (ed.): Dielectric Materials and Applications, New York: John Wiley & Sons, Inc., 1954.