Studies Of Physical Properties Of Perovskite Transition Metal Oxides

The transition metal oxides have been widely studied due to their novel properties,such as superconductivity, colossal magnetoresistance, abnormal Hall effect, huge thermoelectricaleffect and multiferronics. In these system charge, orbital,spin and latticeare coupled to each other,and complicated phase diagrams are introduced the competitionamong these interactions, giving rise to some interesting phenomena such as chargeordering, magnetic ordering, glassy behavior, phase separation, metal-insulator transitionand spin-state transition. Therefore,further understanding of their underlyingPhysical mechanism, such as hybirdizition, wil1 greatly boarden our knowledge on thecondensed mater Physics.In this dissertation, three materials of different p-d hybirdizition are as research objects.We regulate the hybirdizition with high pressure and doping methods, then studythe physical properties of the material. We briefly review the strong correlation systemand the various interactions between electronics. We present a review of the historyand progress of the Perovskite Transition Metal Oxides. Then, we introduce the physicalproperties of Perovskite Transition Metal Oxides,which includes the structuralconsiderations,electronic considerations, electronic considerations, oxygen displacements,transport properties,ordered phase and phase separation. Last, we focus on thephysical properties of iron-based , ruthenium-based and cobalt-based perovskites.We systematically researched charge, spin and lattice interactions in La_0.5Ba_0.5FeO₃of the low levels p-d hybirdizition system. The resistivity and magnetism were strongcorrelation with charge disproportion. The spin state transition of Fe³⁺ at under highpressure-low temperature is found in the magnetization measurement , which is due tothe pressure enlarged the crystal field energy and strengthen the hybirdizition.The electromagnetic property of two series of samples Sr_1-xLa_xRu_1-xCr_xO₃(SCRC)å’ŒSr_1-xCa_xRu_1-xCr_xO₃ (x= 0.04, 0.08 and 0.12) have been designed and investigated.We found the reason of enhancing the ferromagnetism in the SrRu_1-xCr_xO₃system, that is Ru⁵⁺-O^2-Cr³⁺ superexchange interaction.A detailed magnetic study has been carried out for the Ti-doped La_0.5Ba_0.5Co_1-xTi_xO₃(x=0, 0.05, 0.075, 0.10, 0.125 and 0.15) cobaltites. The spin states of Co ions does notchange and stabilize in the intermediate spin state. With introducing Ti ions at B site,it enlarged the crystal constant and Co-O bond length. Then it weakened the doubleexchange interaction and the ferromagnetic Curie temperature. When ferromagnetic interaction weakened to a threshold, antiferromagnetic exist in the system. At low temperature,the system is in a reentrant spin glass state due to the competition between theferromagnetic interaction and the antiferromagnetic interaction. Thus, we established amagnetic phase diagram.A magnetic study has been carried out for the R-doped La_0.5Ba_0.5Co_0.9R_0.1O₃(R=Cu, Zn, Cr, Ni, Ti and Ru) cobaltites. All ions doping stabilized the intermediatespin state of both kinds of Co ions. For R = Zn²⁺, Cu²⁺, Ni³⁺, Ti⁴⁺ and Ru⁴⁺, it decreasesTC and presents a complex magnetism which are closely related to Co3+/Co4+,the B site average cationic radius(.rB.), the tolerance factor(f) and ions itinerant character.Whereas in contrast, doping with Cr³⁺ increases TC. We presume that the Co-OCrexchange interaction exists in system and enhances the ordering temperature. Thisinteraction is confirmed experimentally by ESR spectra. It can deduce that the ferromagneticexchange interaction comes from Cr³⁺(t_2g³e_g⁰)-O-Co³⁺(t_2g⁵e¹_g) andCr³⁺(t³_2ge_g⁰)-O-Co⁴⁺(t⁴_2ge_g¹)。...