CERIUM DISTRIBUTION COEFFICIENT AND ITS DEPENDENCE ON OXYGEN PARTIAL-PRESSURE IN ND2-XCEXCUO4 SINGLE-CRYSTAL GROWTH

A strong dependence of the cerium distribution coefficient (K(Ce)) on oxygen partial pressure P[O2] has been shown in direct TSFZ experiments by changing the oxygen pressure during Nd2-xCexCuO4 single crystal growth. The ratio of K(Ce)0.1 atm/K(Ce)0.2 atm has been found to be equal to approximately 0.62. Absolute values of K(Ce) measured from zone compositions have been found to be about 2.42, 3.37 and 9.06 at P[O2] = 0.1, 0.2 and 2.0 atm, respectively. C)ur experiment shows good agreement between measured and calculated K(Ce) values. We have shown that the quite large difference in K(Ce) obtained in a number of investigations is explained by a strong dependence of K(Ce) on P[O2]. We have also shown that a reason for this dependence is the variable valence of Ce. Cerium effectively incorporates in a Nd2-xCexCuO4 single crystal in the form of Ce+4 ion.