Silver Doping (Pr_1-xLa_x)_0.7Sr_0.3MnO₃(0?x?0.4)Polycrystalline Ceramic Preparation And Its Electrical Transport Properties

Strongly correlated manganese oxide Re_1-xAe_xMnO₃(Re is the Pr³⁺?La³⁺,and Ae is the Sr²⁺?Ba²⁺?Pb²⁺)is belong to a kink of rare earth-doped manganese oxides with a perovskite structure.Attributed to the excellent electrical properties,such as CMR effect,the Re_1-xAe_xMnO₃ have been studied by scientists.In recent years,the focus of more research has shifted to devices,such as spintronic devices,magnetic sensors and infrared bolometer(IR).The temperature coefficient of resistance(TCR)plays a key role in IR.Researchers have done much works on La-based manganese systems.The researchers have successfully solved the three major problems of T_k and T_p values far from room temperature,lower TCR values.Thus La AMnO₃ is a candidate material for uncooled bolometer.However,the attention of electrical properties on Pr-based systems is less.According to the ferromagnetic phase diagram of Pr_1-xSr_xMnO₃,it is known that the material has the strongest electromagnetic coupling at x=0.3.Thus,Pr_0.7Sr_0.3MnO₃ is used as the base ratio.The La-doped or modulated Pr/Sr ratio to change its electromagnetic properties,so as to obtain the Pr system material with room temperature TCR value.Then Ag₂O as the second phase composite to further improve the room temperature TCR value of the sample.Firstly,a series of(Pr_1-xLa_x)_0.7Sr_0.3MnO₃(x=0,0.10,0.20,0.25,0.30 and 0.40)polycrystalline ceramics were prepared.The resistivity gradually decreased with La content increased.The main peak of the crystal structure had a tendency to shift from single peak to double peaks.The T_p values gradually shifted toward the high temperature region.At x=0.25,the TCR value is 5.03%K^-1 and T_k is 299.37 K,reaching the room temperature.Secondly,the(Pr_0.75La_0.25)_0.7Sr_0.3MnO₃ material system with T_k and T_p reaching room temperature was selected,the Ag₂O was doped by solid-phase method to prepare a series of(Pr_0.75La_0.25)_0.7Sr_0.3MnO₃:Ag_x(x=0,0.05,0.1,0.15,0.2,0.25)composite materials.The results showed the crystal structure unchanged and the grain size increased.The resistivity decreased,while the T_p and T_k values remained almost unchanged.The T_k values remained at room temperature.TCR reaching the maximum value at x=0.15(11.35%K^-1(T_k=300.69 K)).The effect of varying the Pr/Sr ratio on Pr_1-xSr_xMnO₃(0.3?x?0.35)was investigated.At x=0.35,TCR value is 5.77%K^-1(T_k is 298.63 K),reaching the room temperature.To further enhance the room-temperature TCR of PSMO ceramics and to analyze the mechanism of Ag₂O doping mechanism,a series of Pr_0.65Sr_0.35MnO₃:Ag_x(x=0,0.04,0.08,0.12,0.16 and 0.2)composite were prepared on the basis of Pr_0.65Sr_0.35MnO₃.The results show that Ag₂O is present in two forms,the main part is precipitated at the grain boundaries in the form of Ag,followed by a small part in the form of Ag⁺replacing Pr/Sr ions at the A-site.The addition of Ag₂O does not change the crystal structure of Pr_0.65Sr_0.35MnO₃.The TCR maximum value is 11.02%K^-1 at x=0.16(T_k=300.05 K).In summary,the(Pr_0.75La_0.25)_0.7Sr_0.3MnO₃:Ag_0.15 and Pr_0.65Sr_0.35MnO₃:Ag_0.16 composite materials were achieved high room temperature TCR values(?10%K^-1,T_k=300 K).This result provides a reference for the application of Pr-based manganese oxide materials in advanced uncooled infrared bolometer and other optoelectronic fast devices.