5585

5219

كارشناسي ارشد

ماده چگال

اصفهان: دانشگاه صنعتي اصفهان، دانشكده فيزيك

1389

[هشت]،88ص.: مصور،جدول،نمودار

ص.ع.به فارسي و انگليسي

پرويز كاملي

هادي سلامتي

7/10/89

فرهاد شهبازي، مهدي رنجبر

فيزيك

ID5219

به فارسي و انگليسي: قابل رويت در نسخه ديجيتالي

Investigation of grain size and ionic radius effects on structural magnetic and electrical properties of La0 5 Ca Sr 0 5MnO3 manganite Student name Payvand Amirzadeh Email address p amirzadeh@ph iut ac ir Date of submission 1389 8 3 Department of Physics Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Supervisor Dr Parviz Kameli kameli@cc iut ac ir Abstract In this thesis We report on the fabrication and characterization of La0 5Ca0 5MnO3 LCMO with different grain size from nanometer up to micrometer The samples have been prepared by new solid state method and their structure magnetic and electric properties have been investigated In the second part of this project the effect of cation size on the structure magnetic and electrical properties of La0 5Ca1 x Srx MnO3 LCSMO 0 x 0 5 which is prepared at temperature 1350oC have been studied X ray diffraction of LCMO samples shows that grain size increases with increase of sintering temperature without any variation in structure The structural parameters and space groups have been obtained by FULLPROF soft ware Rietveld refinement It shows that all the LCMO samples have orthorhombic structure with pnma space group and by increasing of sintering temperature unit cell volume decreased SEM images show that in the sample with sintering temperature of 800oC grain sizes are in range of nanometer and in the sample with sintering temperature of 1200 oC and1350oC are in the range of micrometer The ac magnetic susceptibility measurements showed that all LCMO samples have a PM FM transition and with increase in sintering temperature the charge ordering and AFM phases were observed Curie temperature Tc decreases by growing of crystallite size and suppressed FM phase and induced robust CO and AFM phases at the low temperature that explain with Core Shell model Samples have thermal hysteresis because of coexistence of the FM and AFM phases and phase separation which is a characteristic of first order transition All LCMO samples have a insulator behavior Sample with sintering temperature of 800oC has lowest resistance and sample with sintering temperature of 1350oC has highest resistance Rietveld refinement for LCSMO samples shows that all compounds with x 0 3 crystallize in the orthorhombic structure with space group of pnma and x 0 4 and x 0 5 compounds have tetragonal structure with space group of 14 mcm This structural variation is due to substitution of Ca by Sr and unit cell volume increase with Sr2 doping All the LCSMO samples have a PM FM and FM AFM transition that with increase of Sr2 doping AFM phase decreased and FM phase increased and consequently thermal hysteresis has been decreased All compounds with x 0 4 have insulator behavior and by increase of Sr2 doping resistance decreased Sample x 0 5 shows metal insulator transition Kay words Manganite Thermal hysteresis ac susceptibility Sr doping Charge ordering FM AFM

پرويز كاملي

هادي سلامتي

فرهاد شهبازي، مهدي رنجبر