Facile microwave assisted combustion synthesis, structural, optical and magnetic properties of La2−Sr CuO4 (0 ≤ x ≤ 0.5) perovskite nanostructures

Strontium doped lanthanum cuprate perovskite-type nanostructures were synthesized by facile microwave assisted combustion method. The structural, optical, morphological, and magnetic properties were studied by using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX), photoluminescence (PL) and vibrating sample magnetometer (VSM) techniques.The XRD patterns of pure La 2 CuO 4 (LC) and La 1.9 Sr 0.1 CuO 4 confirmed the formation of perovskite structure without impurities. However with the increase in Sr 2+ content from ( x = 0.2–0.5), phase transformation from orthorhombic to tetragonal structure, occurred. The average crystallite size of orthorhombic and tetragonal phases were in the range 39.6–47.4 nm and 22.3–88.0 nm, respectively. The presence of tensile strain in Sr 2+ doped LC (LSC) was determined from Williamson–Hall (W–H) analysis. The appearance of FT-IR bands at around 688 and 521 cm -1 were correlated to the La-O and Cu-O stretching modes of orthorhombic La 2 CuO 4 phase. The direct band gap estimated using Kubelka–Munk (K–M) method increased with increasing Sr 2+ content (1.88–2.03 eV), due to quantum confinement. For LC and LSC, PL spectra showed emission bands in UV and visible regions, due to the defect centers acting as trap levels. The LSC system showed the formation of nanosized crystallized grains with pores and pore-walls due to fused grains. Magnetization–Field (M−H) hysteresis curves revealed the appearance of ferro-/para- magnetic behavior at room temperature.