Bahattin Düzgün

An investigation of the Nb doping effect on structural, morphological, electrical and optical properties of spray deposited F doped SnO2 films

F and Nb + F co-doped SnO2 thin films were deposited on glass substrates by the spray pyrolysis method. The microstructural, morphological, electrical and optical properties of the 10 wt% F doped SnO2 (FTO) thin films were investigated specifically for niobium (Nb) doping in the range of 0–4 at.% with 1 at.% steps. As shown by the x-ray diffraction patterns, the films exhibited a tetragonal cassiterite structure with (200) preferential orientation. It was observed that grain sizes of the films for (200) and (301) peaks depended on the Nb doping concentration and varied in the range of 25.11–32.19 and 100.6–183.7 nm, respectively. The scanning electron microscope (SEM) micrographs showed that the FTO films were made of small pyramidal grains, while doubly doped films were made of small pyramidal grains and big polyhedron grains. From electrical studies, although 1 at.% Nb doped FTO films have the lowest sheet resistance and resistivity values, the highest figure-of-merit and optical band gap values obtained for FTO films were 16.2 × 10−2 Ω−1 and 4.21 eV, respectively. Also, infrared reflectivity values of the films were in the range of 97.39–98.98%. These results strongly suggest that these films are an attractive candidate for various optoelectronic applications and for photothermal conversion of solar energy.

Indentation Size Effect and Microhardness Study of β-Sn Single Crystals

The load dependence of apparent microhardness of ?-Sn single crystals having different growth directions is investigated. The measurements are performed on (110) planes of these crystals in the load range from 10 to 50?mN. It is found that the degree of the microhardness anisotropy decreases for higher indentation test loads. The examined materials exhibit the behaviour of indentation size effect (ISE), i.e., the apparent hardness increases with decreasing indentation load. Neither Meyers law nor the proportional specimen resistance (PSR) model can fully explain the nonlinear variation of microhardness with load. Instead, preference is given to modified the PSR model based on the consideration of the effect of machining-induced residually stressed surface on the hardness measurement.

The Temperature Dependence of Work-Hardening Rate in Invar Fe–Ni Alloys

The stage I work-hardening behavior of Invar Fe-Ni alloys was studied in tension in the temperature range from room temperature to 700 K. Work-hardening rate (WHR) is a function of temperature and has a peak at about 560 K. The anomalous strength is attributed to thermally activated cross-slip.

Orientation and temperature dependence of slip systems in Cd single crystals

The orientation and temperature dependence of slip in Cd single crystals has been investigated in tension in the temperature range from room temperature to 480 K. At room temperature, slip occurs along directions on the basal plane regardless of crystals orientation. On the other hand, above 350 K operative slip directions are found to be depending on crystal orientation and slip planes.

STEADY-STATE CREEP DEFORMATION OF Cd SINGLE CRYSTALS

The creep behaviour of Cd single crystals has been investigated in tension in the temperature range from 300 Κ to 450 K. The activation energies and the stress exponents of steady-state creep were calculated. The dependence of steady-state creep rate on the stress and temperature show a possible change in the rate-controlling mechanism for creep.

The Effect of Crystal Diameter and Orientation On Plastic Deformation in White Tin Single Crystals

The stress-strain curves of white tin single crystals have been determined as a function of crystal diameter and orientation at room temperature. The stress-strain curves, especially for thinner crystals, are characterized by a remarkable decrease in stress after yielding followed by a gradual increase in the stress with strain due to work hardening. On the other hand, the easy glide region was found to be a function of both crystal diameter and orientation.

Deformation Twinning in Cd Single Crystals

Deformation twinning in hexagonal-close-packet (Lc.p.) crystals has been investigated under tension at room temperature. It was found that deformation twinning is possible in Cd single crystals at room temperature. But twinning was observed only in a limited number of crystallographic orientations, and twinning stress changed according to these orientations.