Second harmonic generation study of local polar inhomogeneities in Pb3(MgNb2)O9

The temperature dependence of the second harmonic generation in the lead magnesium niobate (Pb 3 (MgNb 2 )O 9 ) crystal has been studied. It has been shown that the second harmonic generation in the crystal occurs in local non-centrosymmetric regions in the sample bulk, whereas a similar response from a fine powder is caused by effects associated with decreasing grain sizes. Maximum changes in polarization in local regions occur near the Vogel-Fulcher temperature in the range of 200–270 K. In the same temperature range, according to the published data, gradual freezing of polar regions and the formation of an infinite cluster is assumed.