Structural, electrical transport and optical properties of doped La0.7Ca0.3MnO3 ceramics

[Display omitted] In this study, we have investigated the structural, electrical transport and UV–Visible properties of polycrystalline La0.7Ca0.3−xKxMnO3 (x=0.0, 0.05, 0.10, 0.20) ceramic samples prepared by conventional solid-state reaction. The structure characterized by X-ray diffraction shows that the samples possess orthorhombic perovskite structure belonging to Pnma space group with some impurity for higher doping level (x=0.10, 0.20) and cell volume is enlarged with Ca2+ substitution by K1+. The surface morphology was investigated by field emission scanning electron microscope, which indicates that the samples with better crystallization having higher density. The electrical transport properties were measured by the standard four-probe method, which demonstrates that the resistivity decreases non-monotonically and the metal–insulator transition temperature (TP) shifts to higher temperature with increasing K1+ content, the electrical transport behavior for metal and insulator region was explained using Zener double exchange model and small polaron hopping model respectively. Furthermore, the progressive substitution of Ca2+ by K1+ broadens the metal–insulator transition and reduces the temperature coefficient of resistivity. Room temperature UV–Vis studies show that the optical band gap changes with the partial replacement of Ca2+ with K1+. The investigations clearly show the effect of impurity present on structural, electrical transport and UV–visible response of the prepared ceramic samples. En este estudio, hemos investigado las propiedades estructurales, de transporte eléctrico y UV-visible de muestras cerámicas policristalinas de La0.7Ca0.3-xKxMnO3 (x=0,0, 0,05, 0,10, 0,20) preparadas por reacción convencional en estado sólido. La estructura comprobada por difracción de rayos X muestra que las muestras poseen una estructura perovskita ortorrómbica perteneciente al grupo espacial Pnma con algunas impurezas para niveles de dopaje más altos (x=0,10, 0,20) y el volumen de las celdas se amplía con la sustitución de Ca2+ por K1+. La morfología de la superficie se investigó mediante un microscopio electrónico de barrido de emisión de campo, que indica que las muestras con mejor cristalización tienen mayor densidad. Las propiedades de transporte eléctrico se midieron mediante el método estándar de cuatro sondas, que demuestra que la resistividad disminuye de forma no monótona y la temperatura de transición metal-aislante (TP) se desplaza a una temperat