Crystal Structures And Properties Of Ba₂FeMoO_6-xF_x And La_0.67Sr_0.33MnO_3-xF_x

Magnetoresistance effect is one of the main properties in the study of perovskite magnetic materials.Doping is an effective method of material modification.In recent years,fluorine^-ion doped hybrid halide perovskite solar cells has been used to study materies modification.In addition,it was also applied to modify the electrical transmission performance of Ba₂CaNbO_5.5.5 and Ba₂InO₅?perovskite-like?with double perovskite structure.The structure of F^-ions doped in perovskite and double perovskite has been rarely studied in theoretical research on its structure electrical and magnetic.Ba₂FeMoO_6-x-x F_x and La_0.67Sr_0.33MnO_3-x-x F_x series samples were synthesized by standard solid state technique.which used to study the structure and electromagnetic properties.Ba₂FeMoO_6-xF_x series samples crystallize in cubic system with Fm-3m space group.It is found that the oxidation number of some B sit ions decreases due to the incorporation of fluorine ions.Therefore,the overall unit cell volume appears to increase with the increase of fluorine^-doped.According to the magnetic analysis of the samples,the samples were all ferromagnetic in the measured temperature range,and the the T_C values of the sample decreases with the increase of F content,and T_C varies from 316 K to 343 K.Through electrical analysis,all the samples of the series have negative magnetoresistance.La_0.67Sr_0.33MnO_3-xF_x series samples crystallize in rhombohedral structure with R-3c space group.On the whole,the unit cell volume increases with the increase of fluorine content.The samples of series are shown to be ferromagnetic materials.the T_C values are found to decrease and move into the cold temperature with fluorine^-ion substituted,which are the results of the reduction of bandwidth due to the weakening of double-exchang.All the samples showed large negative magnetoresistance effect,and the MR value rate of x=0.15 sample is the highest at room temperature.From the?-T curve of samples?x=0?x=0.05?x=0.10?,the transition temperature from metal to insulator observed.According to the?-T curve of samples?x=0.15?x=0.2?,it is obvious that there are double peaks.One that the temperature value corresponding to the transition from metal to insulator(T_p1),the other is(T_p2).The T_p value of all samples is significantly moved towards high temperature zone with the external magnetic field.The reason is that the presence of oxygen deficiency makes the change of resistivity with the doping amount not monotonous.Undoped F-ion samples may have oxygen vacancy,resulting in increased resistivity,However,the sample doped with F^-ions may have an oxygen vacancy,which may lead to an increase in the conductivity of oxygen ions,namely,a decrease in the resistivity of the sample.The conductive models of the semiconductor part of the series are all small polaron adiabatic transition conductive models.The electrical transport performance of metal parts is more complex and conforms to a variety of conductive mechanisms.