Influence of structural disorder on the optical and transport properties of Co0.50Ti0.50 alloy films

Co0.50Ti0.50 alloy films with a total thickness of about 100 nm were prepar ed by flash evaporation of the crushed alloy powders onto heated (730 K for the ordered state) and LN2-cooled (150 K for the disordered state) substra tes. Structural analysis of the films was performed by using transmission e lectron microscopy. The optical conductivity (OC) of the samples wits measu red at room temperature in a spectral range of 265 - 2500 nm (4.7 - 0.5 eV) . The resistivity measurements were carried out by using the four-probe tec hnique in a temperature range of 4.2 - 300 K. The experimental OC spectra f or the Co0.50Ti0.50 alloys show the most significant changes in the infrare d region upon the order-disorder transformation The structural disorder in the Co0.50Ti0.50 alloy film leads to a change in the sign of the temperatur e coefficient of the resistivity from positive to negative. The observed ch anges in the optical properties and the temperature dependences of resistiv ity caused by the order-disorder structural transition are analyzed in the framework of the lattice symmetry and the electronic structure of the order ed CoTi compound.