ساخت منگنايت پروسكايتي La0-8 pb0-2 mno3 به روش آلياژسازي مكانيكي و بررسي خواص ساختاري، مغناطيسي و الكتريكي آن

چكيده انگليسي :

AbstractIn this project our intent was to produce La0 8Pb0 2MnO3 LPMO nanocrtystalline samples fromoxide precursors Mechanical alloying MA is a solid state powder processing techniqueinvolving repeated cold welding and fracturing of powder particles in a high energy ball mill MA offers a simple processing route of materials with large quantities and at relatively low cost In first section of this project the effect of crystallite size on structural and magnetic properties ofpowder La0 8Pb0 2MnO3 was investigated The samples were characterized using X ray diffraction The results showed that it is possible to produce LPMO perovskite powders after 10h ofball milling The XRD pattern of samples reveals that all samples are single phase withrhombohedral crystal structure The crystallite size and microstrain were estimated usingWilliamson Hall equation The results show that the crystallite size and microstrain initiallyincreases and then decreases by the increase of milling times By decreasing crystallite size thedislocation density strain increases and reaches to a saturation point at a particular grain size further particle size reduction takes place through gliding motion along grain boundaries whichleads to a reduction takes place through gliding motion along grain boundaries which leads toreduction of the strain The FT IR investigation shows that the Jahn Teller distortion increaseswith the decreasing in the crystallite size Magnetic susceptibility measurements showed that themagnetization and the transition temperature decline with decreasing of the crystallite size Thedynamic properties of 15h ball milled sample were investigated by Ac susceptibility using theNeel Brown and Vogel Fulcher law for superparamagnetism The frequency dependence ofblocking temperature is well described by the Vogel Fulcher law and fitting the experimentaldata with Neel Brown law shows unphysical value for relaxation time In the next section we have investigated the effect of sintering temperature on structural magnetic and electrical properties of La0 8Pb0 2MnO3 For this purpose the 15h ball milled powderwere pressed under the 1 Gpa pressure and sintered at different temperatures The obtainedsamples were characterized by X ray diffraction scanning electron microscopy SEM andmagnetic measurements Room temperature X ray diffraction of sintered La0 8Pb0 2MnO3 showsthe formation of homogeneous single phase compound with rhombohedral perovskite structure Also X ray diffraction of these samples shows the increasing crystallite size by increasingsintering temperature Magnetic susceptibility measurements showed that the magnetizationincreases with the increases of crystallite size In other hand on decreases of real part of Acsusceptibility one more peak appears in the imaginary component for 1200 and 1350 oC sinteringsamples To further investigate this behavior we have measured the Ac susceptibility of samplesat different frequencies and magnetic fields The low temperature peaks shift toward the highertemperature by increasing of the frequency and shift to the low temperature with increasingmagnetic field We have checked the possibilities of spin glass behavior thorough a conventionalcritical slowing down model The best fited parameters from a log log plot of the reducedtemperature Tf Tg T g versus external frequencies are T g 60 K and zv 11 25 for 1350oC sample The estimated values are within the realm of three dimensional spin glass In order to study thetransport properties of the samples the temperature dependences of the resistance R T weremeasured The metal insulator transition could not be observed in all samples To explain thetransport properties described above the interface layers between grains have to be considered Inthe milling process many defects were inevitably produced in the interface layers due to theintrinsic characteristics of ball milling Oxygen vacancies break parts of the Mn3 O2 Mn4 network introduce forbidden paths for conductance el

بهرامي، حسين

ساخت منگنايت پروسكايتي La0-8 pb0-2 mno3 به روش آلياژسازي مكانيكي و بررسي خواص ساختاري، مغناطيسي و الكتريكي آن

رابطه ي ويلياسيون - هال , فيزيك منگنايت