Effects of a-site and b-site substitution on the structural, magnetic and electrical properties of bi-doped La0.7Pb0.3-xBixMnO3 and v-doped La0.7Pb0.3Mn1-yVyO3 manganites / Muhammad Afiq Ikhwan Zainuddin

Substitution of paramagnetic metal cations onto the A-site and B-site appears to influence the lattice stability and electron conduction behaviour of perovskite-type compounds. The variation of structural, electrical, and magnetic behaviour in perovskite manganites La0.7Pb0.3-xBixMnO3 (x = 0 – 0.04) and La0.7Pb0.3Mn1-yVyO3 (y = 0 – 0.1) was studied and reported in the present dissertation. Each compound was prepared according to the conventional solid-state synthetization method. All the samples crystallized in a rhombohedral structure with a space group of R-3c. A clear transition peak of the metal-insulator was observable in both samples, with variation in TMI values. The TMI values of La0.7Pb0.3-xBixMnO3 (x = 0 – 0.04) compound decrease from 292 K (x = 0) to 256 K (x = 0.04) while the La0.7Pb0.3Mn1-yVyO3 (y = 0 – 0.1) TMI’s value also exhibits the same pattern, dropping from 292 K (y = 0) to 250 K (y = 0.1). The deterioration of the TMI value was due to several factors, such as variations in cell parameters, MnO6 octahedral distortion, and the existence of hopping mechanism competition introduced by dopants (Bi and V) may affect the itinerant electron double-exchange (DE) behaviour, causing the TMI value to shift away from room temperature (300 K). Further discussion on the electrical behaviour of the samples was elucidated via mathematical fittings to determine the most appropriate, eg electron conductivity behaviour in the metallic region (30 K < T < TMI) and insulating region (300 K > T > TMI). All the samples exhibited a smooth magnetic phase transition curve from ferromagnetic (FM) to paramagnetic (PM) with different Curie temperature (TC) values. A declining pattern of TC value can be observed in all the samples as the dopant (Bi and V, respectively) increases. An assumption can be constructed where the electron hopping between Mn3+ – O2- – Mn4+ is suppressed due to the Mn – O bond angle and length alteration induced by the dopant element. Furthermore, substituting V at B-site of La0.7Pb0.3MnO3 may alter the Mn3+/Mn4+ stoichiometry ratio, further disrupting the electron DE mechanism. In summary, the substitution of Bi at the A-site and V at the B-site of the La0.7Pb0.3MnO3 compound resulted in alterations to its structure, electrical properties, and magnetic characteristics.