Powder Reduction And Bulk Sintering Conditions Of Mno The La <sub> 0.67 </ Sub> Of Sr <sub> 0.23-x </ Sub> The Cu <sub> 0.10 </ Sub> ¡õ <sub> X </ Sub> < Sub> 3 </ Sub> (x = 0,0.03) Materials, Ma

Since the 1990's, When the colossal magnetoresistance (CMR) effect in rare-earth manganite perovskites was found, it has attracted considerable attention of scientists and engineers due to its special physics mechanism and the potential application in fields of magnetic record and magnetic sensor and so on.However, the poor temperature dependence of magnetoresistance (MR), the ideal MR occurred only in high field and the low-temperature for the most materials, severely limit their practical utilities. Many researches have thus been concentrated on making new material system that provides low field magnetoresistance (LFMR) around room temperature. On the other hand, recent efforts to broaden the CMR temperature range have been made by means of the Mn-site substitution or oxygen-deficiency.In this paper, La_0.67Sr_0.23-xCu_0.10â–¡_xMnO₃(x=0,0.03) polycrystalline powders were prepared by sol-gel method, which we used as parent materials. The parent powders were reduced by hydrogen in different conditions, and series of reduced powders were prepared. The bulk samples sintered in an Ar and air atmosphere respectively. Their structure, morphology, electrical and magnetic properties as well as magnetoresistance were researched in detail. There are several results we have got:1. Morphologies of La_0.67Sr(0.23-x)Cu_0.10â–¡_xMnO₃(x=0, 0.03) parent powders and reduced powders were obtained by S-570 scanning electron microscopy (SEM). The results show that the particles in powder samples are closed to globular shape and the particle size is nanometer order. The phenomenon of conglobation in particles was improved by reducing treatment.2. The phase identification of samples has been carried out by the X-ray diffraction (XRD) with a Rigaku D_Max(12KW) diffractometer. The results indicate that the Mn₃O₄ impurity phase in the samples could decrease or disappear by reducing treatment in a hydrogen atmosphere at proper temperature.3.Under an applied magnetic filed of 1.8T, The two bulk samples sintered in Ar atmosphere for 12 hours at 1100℃, with the powder reduced for 30 and 60 minutes in 400℃ hydrogen atmosphere for La_0.67Sr₍0.20_Cu_0.10â–¡_0.03MnO₃ parent powders, respectively, have the stable MR (11.0±0.3) % and (10.0±0.5) % in temperature range between 270K and 330K. It is important for the potential application of this kind ofmagnetoresistance material.4. Under an applied magnetic filed of 1.8T, the maximum values of MR, MRP, of the samples sintered in Ar atmosphere for 12 hours at 1100°C, with the powder reduced for 15 minutes in different temperature (2.00°C, 250°C, 300°C) hydrogen atmosphere for Lao.67Sro.2oCuo.io[Ilo.o3Mn03 parent powders, respectively, were improved comparing to one of the sample sintered with the parent sample. The MR? of the sample sintered with parent powder is 24.6% at 319K;the MRf of the sample sintered with powder reduced for 15 minutes at 250°C, reaches 31.5%.5. On the basis of the studies about the dependence of Curie temperature of the several powder and bulk Lao.67Sr0.2oCuo.io!Ho.o3Mn03 samples on the conditions of reducing powder and sintering bulk, there are several results as follows:First, the perovskite crystal grain size and oxygen content in the lattice have a significant effect on the samples' magnetic variation in the transition zone from ferromagnetism to paramagnetism. The effect can be described by the maximum valueofdadTUm=dadT, in which a represents magnetization and T representsMAXtemperature. As the crystal grain size increasing, um increases;as the oxygen content in lattice deviating from standard value 3.00,wm decreases.Second, the oxygen content in the lattice of Lao.67Sro.2oCuo.ioDo.o3Mn03 parent powder sample PI exceeds standard value 3.00. The oxygen content in the lattice of the powder sample P2, being reduced by hydrogen for 15 minutes at 200°C, approaches the standard value 3.00. Both higher reducing temperature and longer reducing time can make the oxygen content in the lattice of powder sample lower than standard value 3.00;the reducing temperature or reducing time increases, the oxygen content decreases.Third, sintering bulks in Ar atmosphere has no obvious effect on the oxygen content in samples;Sintering bulks in air atmosphere can make oxygen content in the lattice be higher than standard value 3.00, the sintering temperature or sintering time increases, the oxygen content exceeds standard value;for bulk samples sintered in air atmosphere, the lower oxygen content in the lattice of its powder is, the fewer oxygen content in the lattice of bulk samples exceed standard value 3.00, the higher magnetization the samples have.In conclusion, reducing the powder in the suitable temperature hydrogen for suitable time interval, could improve the maximum value of MR and the value of MRnear room temperature of the Lao.67Sro.20Cuo.10 D o.o3Mn03 bulk samples. The temperature stability of MR near room temperature can also be improved.