Electrical Properties of Li_<i>x</i>Ni_(1-<i>x</i>)O Single Crystals

Abstract

Aiming at a better understanding of still vague conduction processes in NiO, extensive measurements of the electrical resistivity ρ were made between 300 and 1020°K on Li x Ni (1- x ) O single crystals epitaxially grown on the MgO substrates, where x from zero up to 0.065 was controlled by diffusion method. The main results are as follows: (1) log ρ(/ T ) vs 1/ T forms two straight lines, folded at a transition temperature T * . Each T * is close to the Néel temperature of NiO but a slight decreasing function of x . (2) With increasing x two activation energies ε 1 ( T > T * ) and ε 2 ( T < T * ), their difference ε 2 – ε 1 , and ρ sharply decrease at first (3) When x increases above 0.015, ε 1 approaches a final constant of 0.14 eV, and ε 2 – ε 1 to k T * with a maximum error of 20%, while ρ still exhibits a gentle decrease. (4) ε 2 – ε 1 always has the positive sign which is opposite to that of early sintered samples. These results are discussed in terms of Toyozawa's hopping model. The initial rapid decrease in ε 1 , ε 2 , and ρ with increasing x is explained by the sharp decrease in the attracting potential of neighboring Li + ion, and the saturation value of the activation energy corresponds to the activation energy for the hopping process.