Axial stoichiometry variations in lithium niobate crystals grown from near-congruent melts

Eleven lithium niobate crystals were grown using the Czochralski method from melts deviating from the congruent melting composition and the resulting axial variation of the crystal composition was analyzed using Curie temperature measurements. The weight of the melts was 7 kg, and grown crystals had solidifying mass ratios in excess of 90%. A mathematical model to predict axial compositional variations in the crystals was developed and integrated numerically to estimate the value of the effective distribution coefficient. A linear relationship between the effective distribution coefficient and the melt composition accurately describes the solid compositions of crystals grown from melts ranging from 45.1% to 51.7% Li2O. It is shown that for growth conditions suitable for volume production and large crystal diameters, the difference between the effective and equilibrium distribution coefficient is well below 0.2%.