Electrical and Optical Properties of Nanosized Perovskite-type La_0.5Ca_0.5MO₃ (M=Co,Ni) prepared using a Sol-Gel Method

Abstract

In this paper the uniform nanopowders of La_0.5Ca_0.5CoO_3–δ and La_0.5Ca_0.5NiO_3–δ (LCCO and LCNO) were synthesized fromnitrates of the constituent metal ion, citric acid (CA), and ethylene glycol (EG) by the combined citrate-ethylene glycol (EG) method. These nanopowders were also characterized by differential thermal analysis (DTA), X-ray diffraction (XRD), transmission electron microscopy (TEM), SEM-EDX analysis and Brunauer-Emmett-Teller (BET) method. XRD results show that single perovskite phase was completely formed after calcination at 750 °C. Fourier transforminfrared (FTIR) spectra were measured for the xerogels and powder samples after calcination. In addition, the TEM images show that the average particle size of nanoparticles is approximately 25–32 nm in diameter. The ultraviolet (UV) spectrum was used to calculate the absorption coefficient (α) as a function of photon energy (hυ) and the obtained results indicate that the optical band gap energy (E_g) for LCNO sample is smaller than that of LCCO. Finally, the temperature dependence of the specific resistivity of LCCO and LCNO sintered at 1100 °C was compared and revealed that the resistivity of both compounds decreases exponentially by increasing the temperature.

Keywords: La_0.5Ca_0.5MO₃, perovskite, sol-gel process, nanopowder, optical properties