Study of structural & optical properties of pure and Ca doped PrMnO3

Abstract

Manganese oxides with the perovskite structure have been the subject of numerous papers since the discovery of large magnetoresistance in these materials. These manganites with the generic formulation Ln1􀀀xAxMnO3 (A = Ca, Sr, Pb, Ba etc.) exhibit a decrease of the resistance on ap- plying a magnetic eld near their Curie temperature (Tc) so that their magnetoresistance is negative and generally de ned as MR% = " R(0) 􀀀 R(H) R(0) # 100 Manganites with the perovskite structure represent a very important family of oxides which are extensively studied for their colossal mag- netoresistance (CMR) properties. In the present review we discuss the different factors which govern the magnetic and transport properties of these materials e.g. average size of the interpolated cation and mismatch e ect on the A-site. Two parameters must be taken into consideration to explain the magnetotransport properties of these oxides: the hole carrier density and the overlapping of the manganese and oxygen or- bitals. The hole concentration is provided by the amount of tetravalent manganese introduced in the trivalent manganese perovskite LnMnO3, by just replacing partly the trivalent lanthanide cation Ln3+ with a di- valent cation A2+. Thus, the hole carrier density is controlled by the Mn(III)/Mn(IV) ratio. The overlapping of the Mn 3d orbitals and O- 2p orbitals depends on the Mn-Mn distance between two consecutive MnO6 octahedra and on the Mn-O-Mn angle. Band gap tuning accord- ing to the atomic replacement and doping can be a great aid to solar industry.