PROPERTIES OF UNDOPED AND MGO-DOPED LINBO3 - CORRELATION TO THE DEFECT STRUCTURE

A series of LiNbO3 crystals were grown with different Li/Nb ratios and a MgO doping up to 8 mol%. The lattice constants, the permittivities, the elastic compliances, the piezoelectric constants, the birefringence and the pyroelectric coefficient were measured and correlated to the Li2O content or to the MgO content of the crystals respectively. Here the congruent melt was found to be 48.3 +/- 0.1 mol%. Lithium could be incorporated up to about 49 mol% into the LiNbO3 lattice. A sudden change in the physical properties announce a structural phase transition of the LiNbO3 lattice with a higher Li2O content. The experimental results on MgO doped crystals indicate that the ferroelectric properties are dependent on the vacancy concentration of the Nb sites. A defect model for MgO doped LiNbO3 is suggested.