Structure, thermoelectric and electrical properties of bismuth-manganese oxide prepared by mechanochemical method

Abstract

Production of nanomaterials by mechanochemical synthesis is one of the important modern methods in new technology. Mechanochemical technique followed by heat treatment has been used to produce bismuth-manganese oxide from bismuth oxide and manganese dioxide. X-Ray Diffraction (XRD) analysis is conducted evaluate the structure changes during the mechanochemical process. Structure transformation from crystalline to complete amorphous phase was observed after short time of milling. The amorphization mechanism and reaction kinetics are examined in the light of the processing parameters and materials composition. Interdiffusion and distraction of the long rang order structure are the proposed mechanisms for amorphization. Bismuth manganese oxide phase with chemical formula Bi2Mn4O10 was formed after heat treatment at 1073 K. Bi2Mn4O10 partially decomposed to γ-Bi12.8O19.2 and α-Mn2O3. Crystallite size (47.6–102.4 nm) of the formed phases after heat treatment is significantly affecting the electrical properties. Thermoelectric power (S) of present samples was reported and the fraction C of reduced transition metal ions was calculated. The manganese ions concentration N were calculated and found to be increasing from 1.11 X1022 cm− 3 to 1.38 X1022 cm− 3, while the average distance between manganese ions R increased from 0.623nm to 0.647nm. The hopping carrier mobility (µ) of the prepared samples was also calculated at fixed temperature. From studying the conduction mechanism, the present work was found to agree with non-adiabatic process of small polaron hopping.