Investigation on relationship among calcination temperature, grain size, Mn valence and resistivity of Ca_0.75Er_0.25MnO_3−δ powders

As is known that calcination temperature plays an important role on structure and properties of ceramic powders. In order to improve the conductivity of Er-doped CaMnO₃ powders, we synthesized Ca_0.75Er_0.25MnO_3−δ powders at different calcination temperatures from 900 to 1,100 °C by sol–gel auto-combustion method. The relationship among calcination temperature, grain size, Mn valence and resistivity of Ca_0.75Er_0.25MnO_3−δ powders was investigated. The results show that the room temperature resistivity presents V-trend with increase in calcination temperature and reaches the minimum value of 0.8013 Ω m at 1,000 °C. X-ray diffraction patterns and the valence analysis illustrate that the grain size and Mn ions valence, which are related to the resistivity of Ca_0.75Er_0.25MnO_3−δ powders, are also affected by calcination temperature. When the calcination temperature is 1,000 °C, Mn ions valence reaches the lowest point of 3.4766. Scanning electron microscope images demonstrate that the grain sizes of Ca_0.75Er_0.25MnO_3−δ powders increase gradually with increase in calcination temperature. The grain size is moderate and uniform at 1,000 °C, which is an important factor to affect the conductivity.