Influence of thermal annealing on resistivity of metallic glasses

U ovom radu proučavan je utjecaj termičkog napuštanja na otpornost metalnog stakla sastava Zr67Co33. Metalno staklo u obliku tanke trake sintetizirano je UBK metodom (”melt-spinning” tehnika). Napravljena je DSC analiza uzorka metalnog stakla kako bi se utvrdile temperature na kojima započinju procesi kristalizacije (pojavljuju se dva egzoterma). Uzorci su se napuštali na različitim temperaturama, odabranim prema rezultatima DSC-analize, u peći u trajanju od sat vremena. Mjerena je zatim temperaturna ovisnost otpora uzoraka metodom četiri kontakta. Uzorci su hlađeni pomoću helijevog hladnjaka, a temperaturni raspon u kojem se mjerilo je 20 - 280K. Amorfni uzorci pokazali su negativni temperaturni koeficijent otpornosti što se objašnjava efektom slabe lokalizacije, dok je kod nanokristaličnih uzoraka napuštanih na višim temperaturama uočen pozitivni temperaturni koeficijent otpornosti. Napravljena je i rentgenska difrakcija uzoraka napuštanih na temperaturama iznad prvog i iznad drugog egzoterma u DSC-slici. Uočeno je da se najprije izlučuju metastabilne faze koje, na višim temperaturama napuštanja, prelaze u stabilne. Iz difrakcijske slike procijenjena je i srednja veličina zrna u nanokristaličnim uzorcima (20 - 30nm).The influence of thermal annealing on the resistivity of metallic glass Zr67Co33 was studied in this work. The ribbon of the metallic glass was produced by ultra fast quenching with melt spinning method. To find crystallization temperatures, the sample of metallic glass was subjected to DSC analysis (two exotherms were found). The samples were annealed at different temperatures, chosen from DSC measurement, in the furnace for one hour. Subsequently, the temperature dependence of the sample resistance was measured by four probe method. The samples were cooled by helium refrigerator in the temperature range from 20 - 280K. The Amorphous samples shown a negative temperature coefficient of resistivity which is explained by effect of weak localization, whereas in the nanocrystalline samples annealed at higher temperatures, a positive temperature coefficient of the resistivity was observed. The samples annealed at temperatures above the first exotherm and the second exotherm in DSC picture were subjected to x-ray diffraction. It is observed that first the metastable phases are excreted which, at higher annealing temperatures, exceeding the stable phases. From the diffraction patterns the mean size of grains in the nanocrystalline samples was estimated (20 - 30nm)