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In this work, tetravalent Ti doping effect on structural, electrical, and magnetic properties of disordered Sm0.55Sr0.45Mn1- xTixO3 (0.0 ≤ x ≤ 0.2) system was investigated. Unlike the metallic nature of resistivity below Curie temperature TC in parent compound, the Ti-doped composition exhibits only semiconducting-type behavior throughout the measured temperature range. The electrical transport results above TC can be explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. Furthermore, magnetization measurements show drastic reduction of TC, Curie Weiss temperature (θCW) and effective magnetic moment (µeff) due to replacement of Ti4+ at Mn4+ site, which can broke exchange coupling of Mn3+/Mn4+ network, destroy the long-range ferromagnetic order.

A systematic series of polycrystalline compounds of YBaCo4−xNixO7 (0 ≤ x ≤ 0.3) have been synthesized by conventional solid-state reaction technique in order to scrutinize comprehensively the effect of Ni substitution on structural, micro-structural and electrical transport properties. X-ray diffraction patterns recorded at room temperature illustrate the structural phase transition with Ni from hexagonal (P6 3 mc) phase symmetry to trigonal (P31c) phase symmetry. The grain morphology observed via scanning electron microscopy indicates the decrease in grain size with increasing Ni percentage. The EDS analysis indicates that Ni is distributed randomly on Co sites also supports the change in crystal structure. The calculated electrical resistivity revealed the semiconducting nature of all compound with and without magnetic field. The resistivity data supported by using Mott’s variable range hopping (VRH) model to calculate the hopping distance (Rh), hopping energy (Eh) and density of states at Fermi level N(EF). Moreover, resistivity data are well fitted with small polaron hopping (SPH) model to investigate the conduction behaviour in the system. Thus, conduction mechanism carried out electronically induced structural phase changes involves in Ni–O–Ni and Ni–O–Co bond angles and bond lengths.