Alternating-current electrical properties of CaMnO₃ below the Neel temperature

The alternating-current electrical properties of polycrystalline CaMnO₃ were investigated by alternating current complex-impedance analysis, and the dielectric properties were analyzed over the temperature and frequency ranges of 10 to 130 K and 20 Hz to 1 MHz, respectively. Direct-current conductivity and the Seebeck coefficient as a function of temperature also were analyzed. Below 120 K, a Debye-type dielectric relaxation peak was observed. Experimental results implied that the number of charge carriers, which were generated by Mn³⁺, were not sufficient to stabilize small polarons, although it induced lattice distortion by the Jahn-Teller effect. Therefore, the thermal motion of Mn³⁺ between potential minimums produced by lattice distortion in the orthorhombic structure were believed to be the source of dielectric relaxation. The temperature dependence of conductivity of the grain interior (σ_gi) below 120 K was believed to be due to variable range-hopping conduction, where σ_gi≈exp(-T^-1/4).