Segregation study and segregation modeling of Ti in Pb[(Mg1/3Nb2/3)0.60Ti0.40]O3 single crystal grown by Bridgman method

Relaxor ferroelectric 0.60Pb(Mg1/3Nb2/3)O3-0.40PbTiO3 single crystal was synthesized by Bridgman method. The segregation along the length of this crystal was observed by various physico-chemical characterization techniques. First, we note the evolution of the crystalline structure along the length of the as-grown crystals. The tetragonality factor c/a increases from 1.013 to 1.020. This evolution has been correlated with the Ti content determination by flame atomic absorption spectrometry, and it is shown that this is due to the evolution of Ti concentration along the crucible. Furthermore, a continuous increase of the fraction of tetragonal phase with increasing Ti content was observed. Hence, we could compare the experimental data with a standard segregation model and therefore calculate the effective segregation coefficient keff for this composition. This coefficient was found to be equal to 0.849. The variation of the titanium content along the ingot causes an inevitable fluctuation of the dielectric and piezoelectric properties of the single crystal. Due to the increase of Ti concentration, the Curie point was 186 °C at the bottom of the ingot and 222 °C at the top. The piezoelectric coefficient of oriented and poled <0 0 1> samples varies from 1500 to 250 pC/N.