Preparation Of La_1-xCa_xMnO₃ (0.1≤x≤0.4) Thin Film Materials By Spin Coating And Their Electrical Transport Propertie

With excellent physical properties,such as metal-insulator transition and phase separation,perovskite manganese have much attention from scientists,with promising applications in magnetic memory,optoelectronic fast devices,and uncooled infrared bolometers.Passing on the excellent properties of ceramics to films is an urgent problem.In this work,La_0.7Ca_0.3Mn O₃films were prepared by sol-gel spin coating and sintering process was optimized in terms of final firing temperature,final firing time and presentering temperature.Then composition was further optimized by Ca-doping and electrical transport properties were researched,providing a theoretical basis for the fabrication and study of films of perovskite manganese oxide.It also provides high-quality replacement materials for uncooled infrared bolometers.The specific results are as follows:Optimal final firing temperature,final firing time,and presentering temperature were determined analytically and tested by preparing La_0.7Ca_0.3Mn O₃ films through sol-gel spin-coating.All the prepared La_0.7Ca_0.3Mn O₃ films were grown along the epitaxial preferred orientation of the La Al O₃（LAO）substrate,and their spatial group was Pnma.The films have low roughness,uniform growth,and smooth surfaces.In the process of changing the final firing temperature,the resistiveity of films decreases first and then increases with the increase of the final firing temperature,and the peak of temperature coefficient of resistivity（TCR）also increases first and then decreases.At 1200℃,the peak of TCR of the film sample is the highest,and its value is 22.59%K^-1,and the corresponding peak TCR temperature（T_k）is 246.85 K.Therefore,the final firing temperature of the experiment was 1200℃after confirmation.The final firing time is the second step of sintering process optimization,and the best final firing time is 6 min.The proportion of Mn⁴⁺in the film samples with the final firing time of 6 min is close to the theoretical value of 33.33%,and the double exchange effect is the strongest.The resistivity of the films first decreases and then increases due to the combined effect of double exchange and Jahn-Teller distortion.In particular,the resistivity of the membrane sample corresponding to 10 min shows an anomalous drop.The TCR of the films first increases and then decreases with the final firing time,with TCR_max of 27.86%K^-1 and T_k of 241.60 K.In the preparation of La_0.7Ca_0.3Mn O₃ films,the influence of the prefiring temperature on the properties of the films was analyzed by varying the prefiring temperature.The degree of distortion of the Mn O₆ octahedra first increases and then decreases with increasing prefiring temperature.The resistivity-temperature curves of the sample films were obtained using the four-probe method.The change of the prefiring temperature has an effect on the resistivity of the film.At the same time,the TCR and T_k of the film samples sintered at 650℃are 24.10%K^-1 and 246.64 K respectively.After determining the optimal final firing temperature,final firing time and prefiring temperature,we explore the effect of Ca-doping on the electrical transport properties of La_1-xCa_xMn O₃ films by varying the doping amount.It has been found that lattice distortion occurs with Ca doping,the Mn-O bond length increases,and the electrical transport properties are affected by the Jahn-Teller effect.The Mn⁴⁺content first increases and then decreases,the Mn content is closest to the theoretical value at x=0.3,and the electrical transport properties change under the influence of the double exchange mechanism.The resistivity decreases with increasing Ca doping content.The PP model fitting for the resistivity and temperature curve of the thin film showed thatρ_4.5,ρ_α,E_a and⁸8)8)8)8)8))together affected the slope of theρ-T curve,resulting in the change of peak TCR.With increasing Ca doping,the TCR of La_1-xCa_xMn O₃films first increases and then decreases,reaching a maximum of 22.92%K^-1 at x=0.3,corresponding to a T_k of 241.93 K.