Preparation And Performance Optimization Of Mn Doped CaTiO₃

Perovskite oxides（ABO₃）are a kind of functional materials with various structures and properties.CaTiO₃ is a typical perovskite oxide and a precursor ferroelectric material with a wide band gap.In order to further expand the application field of CaTiO₃,this paper proposed the method of Mn doped CaTiO₃ to improve its performance through the combination of experiment and theory,and studied the crystal structure,sintering quality,band gap structure and ferroelectric performance of the doping system.This paper attempts to obtain a new narrow gap perovskite oxide material,which may be used in ferroelectric photovoltaic in the future.Firstly,Mn doped CaTiO₃ materials were prepared by solid phase synthesis method on the basis of previous theoretical research of the research group.The results show that the prepared CaTi_1-xMn_xO₃（x=0,0.1,0.2,0.3,0.4,0.5）material is single phase with orthogonal crystal structure of space group Pbnm,and the cell parameters of the materials decrease monotonically with the increase of Mn doping amount.Mn element exists in the form of mixed valence state(Mn³⁺and Mn⁴⁺)in the materials,which is one of the main factors leading to the leakage of CaTi_1-xMn_xO₃ materials.The materials’band gap decreases monotonically with the increase of Mn content,and the band gap of the materials x=0.3,0.4 and 0.5 are in good agreement with the visible spectrum.Mn doping obviously induces the ferroelectric property of CaTiO₃.Then,in order to solve the leakage problem of Mn doped CaTiO₃ material,a certain amount of Nb element is doped into the CaTi_1-xMn_xO₃ system,and excess electrons are introduced through Nb⁵⁺to neutralize the holes introduced by Mn³⁺and reduce the leakage behavior of the system.In this study,CaTi_0.625Mn_0.375O₃ was selected as the theoretical research object,and the effects of Nb doping on the crystal structure,band structure and electronic structure of CaTi_0.625Mn_0.375O₃ were investigated by using first-principles.The results show that the Fermi level guide band of CaTi_0.625Mn_0.375O₃ is shifted by Nb doping.With the increase of Nb doping concentration,Fermi level has a tendency to go further into the conduction band,which makes the material system change from semi-conductive to metallic properties,and shows metallic behavior.Moreover,the band gap of the material system increases with the increase of Nb doping concentration.Finally,Ca[(Ti_1-yNb_y)_0.7Mn_0.3]O₃（y=0.0025,0.0050,0.0075,0.0100）materials formed by Nb-doped CaTi_0.7Mn_0.3O₃ were prepared by solid phase synthesis method to verify the practical effect of Nb doping.The results show that the prepared Ca[(Ti_1-yNb_y)_0.7Mn_0.3]O₃material still has an orthogonal crystal structure with space group Pbnm,and the cell parameters of the materials increase monotonically with the increase of Nb doping amount.Mn element mainly exist in the form of Mn⁴⁺in y=0.0025 materials,but the Mn element coexist in the form of Mn³⁺and Mn⁴⁺when the amount of Nb doping increases further.The band gap increases monotonically with the increase of Nb content,and the band gap of y=0.0025material is in good agreement with the visible spectrum.The ferroelectric property of y=0.0025material is better than that of CaTi_0.7Mn_0.3O₃.In general,Ca[(Ti_0.9975Nb_0.0025)_0.7Mn_0.3]O₃maintains good ferroelectric performance while ensuring that the material band gap can match with the visible spectrum of solar energy.Therefore,Ca[(Ti_0.9975Nb_0.0025)_0.7Mn_0.3]O₃ can be considered as an absorption layer material of solar cells and applied in ferroelectric photovoltaic in the future.