DETERMINATION OF THE CT GAP OF A ND2CUO4-DELTA SINGLE-CRYSTAL BY HIGH-TEMPERATURE CONDUCTIVITY MEASUREMENT

The single crystal was grown by the TSFZ method, and the in-plane and c-axis conductivities were determined as functions of temperature and oxygen partial pressure. Arrhenius plots for in-plane and c-axis conductivity in the intrinsic region fall on straight lines. The in-plane mobility calculated by the combination of conductivity with oxygen nonstoichiometry was nearly independent of temperature and was regarded as 1.33 cm2 V-1 s-1. Assuming the temperature independence of the mobility, the CT gap was determined from the slope of the Arrhenius plot for conductivity. The CT gaps in the ab-plane and along the c-axis were found to be 1.21 and 1.22 eV, respectively. It was concluded that the same band contributes to conduction along the c-axis and in the ab-plane.