Thermoelectric Power Studies on La2-xSrxNiO4-δ

Abstract

ABSTRACTThermoelectric power (S) has been measured on La2-xSrxNiO4-δ. Both nonmetallic (0.5 < × < 1.0) and metallic materials (1.1 ≤ × ≤ 1. 5) have been investigated between 80 and 310 K. The sign of S changes from negative to positive between 150 and 220 K for both metallic and nonmetallic samples. The position at which the curve crosses from negative to positive depends upon the composition (x). For example, when × = 1.15 (metallic conductivity) S changes from negative to positive at about 220 K. However, if this sample is heated to 1000° C under argon, the material becomes nonmetallic and the sign of S remains positive between 80 and 310 K. These results may indicate that more than one type of carrier is involved. The absolute magnitude of S at 300 K decreases with × for 0.5 ≤ × ≤ 1.15 and then increases with × for 1.15 ≤ × ≤ 1.5. In the heavily doped material where S becomes more negative with increasing doping, the thermoelectric power strongly indicates that electrons and not holes are the majority carriers.