Formation of indentation cracks and origin of indentation size effect in cadmium tartrate pentahydrate single crystals

The load dependence of the Vickers microhardness on the as-grown (0 1 0) and (0 0 1), and cleaved (0 0 1) faces of cadmium tartrate pentahydrate (CTPH) single crystals has been investigated. The experimental results showed that, with an increase in the applied load, the microhardness of the as-grown (0 1 0) and (0 0 1) faces decreases, while that of the unheated and heated (0 0 1) cleavage faces decreases first up to a load of 2.5 N and then increases. Analysis of the experimental results revealed that: (1) radial crack length, indentation size and applied indentation load are mutually related, and these dependences related with fracture mechanics are the basis of Meyer’s empirical law, (2) with increasing indentation load, changes in the mechanism of development of indentation cracks from radial cracks to lateral cracks and surface chipping of the material, followed by predominantly surface chipping of the material are responsible for indentation size effect in CTPH crystals, (3) proportional specimen resistance model and Meyer’s law not only explain the indentation size effect but also can be used to determine load-independent hardness H^∗, and (4) there is no direct relationship between microhardness and fracture toughness of different CTPH samples, while the values of load-independent hardness H^∗, and brittleness indices β and B of CTPH crystals increase linearly with the Meyer constant A. Procedures are given to determine load-independent hardness H^∗ from the transition values of load and corresponding indentation size.     

Electrical properties of Li-based NASICON compounds doped with yttrium oxide

In the present study, the electrical properties of lithium-based Li_1.3Al_0.3???x Y _x Ti_1.7(PO₄)₃ (LAYTP) system is reported. Yttrium is a rare earth element and has been found to be an excellent sintering aid in ceramic electrode materials. Earlier attempts to replace the tetravalent Ti⁴⁺ using trivalent cations like Al³⁺, Y³⁺, In³⁺, and Sc³⁺ in rhombohedral NASICON structure have resulted in enhanced electrical conductivity. The effect of trivalent cation Y³⁺ doping in an optimized system Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) is discussed. The electrical properties of this ceramic compound in temperature range of 303 to 423 K and in the microwave frequency range of 20 MHz to 1 Hz were studied for the LAYTP system using impedance spectroscopy. The role of yttrium to improve the density of the material and thereby the study of the grain and grain boundary is explored.     

Photoconducting nanocrystalline lead sulphide thin films obtained by chemical bath deposition

A chemical bath deposition method of preparing photoconducting nanocrystalline lead sulphide (PbS) thin films at room temperature (RT) is described. The aqueous bath of lead acetate, thiourea, and ammonium hydroxide produce films of about 100?nm thicknesses in 45?minutes. X-ray diffraction (XRD) studies show that these films are nanocrystalline cubic PbS with 10?nm crystallite size. Atomic Force Microscope (AFM) and Scanning Electron Microscope (SEM) revealed that the films consist of spherical grains of sizes 100 to 200?nm. The transmission spectra of the films show onset of absorption edge around 850?nm and the bandgap is around 1.65?eV. The films are p-type with dark conductivity of 2.5×10^?3?S/cm and mobility of 0.07?cm²/V?s. The photosensitivity is 6–7 for an illumination of 80?mW/cm² from a halogen lamp (50?W, 12?V). Transient photoconductivity measurements reveal short and long life times of minority carriers. Thermoelectric and photothermoelectric studies show that photoconductivity in these films is mainly due to photogenerated majority carriers.