Structural and Physical Properties of La2/3Ca1/3MnO3 Prepared via a Modified Sol-Gel Method

High purity powder of manganese perovskite, La_2/3Ca_1/3MnO₃, is prepared using a modified sol-gel synthesis based on the dissolution and homogenisation of metal salts in ethanol-acetic acid mixture without using any complexing aid (e.g., polyol or polyhydroxy acid, etc.), which is essentially used in the polymeric precursor routes. This modification minimises the organic contamination in the resulting ceramic that is formed as single perovskite at 650°C, after short calcination time periods. The formation of a monophasic material and absence of second phases or phase segregation was confirmed by powder X-ray diffraction, energy dispersive X-ray and electron microscopy of the ceramic calcined at higher temperatures (800–1400°C). The calcined samples are nanocrystalline up to 1000°C (average particle size, 44 nm) however, significant particle growth is observed at higher temperatures with micron-sized grains present in the sample sintered at 1400°C. The sample exhibits the characteristic colossal magnetoresistance behaviour. Owing to the high chemical and structural purity of the obtained ceramic, the intrinsic bulk features like metal-insulator transition and ferromagnet-antiferromagnet behaviour of the polycrystalline sample are comparable to those observed in the single crystal La_2/3Ca_1/3MnO₃ specimen, used as a reference. The single-crystal-like properties are also corroborated by the observation of a sharp metallic fermi edge in the UPS measurements. The variable temperature photoemission spectra reveal a temperature dependent redistribution of spectral weight close to the fermi level corroborating the temperature dependent resistance and magnetoresistance of the sample. The material shows a homogeneous grain size and a high sinterability as shown by TEM and SEM studies, respectively. XPS study indicates a charge carrier hopping between Mn³⁺(3d⁴) and Mn⁴⁺(3d³) sites.