Electrically controlled light scattering in FLC cells

Abstract— Three types of light‐scattering effects distinguished by physical mechanisms were studied in detail in monomeric ferroelectric liquid‐crystal (FLC) compositions at different boundary conditions and electrical pulse regimes. The total time of the scattering switching on and switching off is less than 150, 250, and 500 μsec at ±50 V for different scattering types in helix and non‐helix FLCs. They are quite fast, and FLC cells are quite transparent and were used in a stack of 30–100 light‐scattering shutters for a volumetric screen of a 3‐D display.     

Investigation of a ceramic in indentation of a Vickers diamond pyramid

The results are given of hardness and crack resistance tests of the surface of silicon nitride- and zirconium dioxide-base material in indentation of a Vickers pyramid. For the investigated materials the presence on the curves of change in these characteristics of areas of stabilization of the mechanisms of deformation and fracture is established and also the fact that one of the reasons for nonlinearity of the strain curves is probably microcracking of the glassy phase and phase transformations occurring in the area of the indentor impression. In addition, a semiempirical relationship most applicable for calculation of K_Ic of the investigated constructional ceramics was determined.Translated from Problemy Prochnosti, No. 9, pp. 49–54, September, 1990.     

Phase transformations in materials studied by micro-Raman spectroscopy of indentations

 Phase transformations occurring in materials under high pressures are important for a wide range of problems in materials science and solid-state physics. Most of the results in this area have been obtained using various sophisticated high-pressure cells. We studied solid-state phase transformations and amorphisation under high non-hydrostatic pressures in very simple experiments using a combination of hardness indentation tests with micro-Raman spectroscopy. Amorphisation of diamond, that did not occur under hydrostatic loading, has been observed. Shearing and distortion of cubic diamond structure above 100 GPa resulted not only in its amorphisation, but also in the formation of threefold coordinated carbon. A carbon film that was squeezed between a SiC substrate and diamond indenter lost its graphitic structure and produced a Raman band typical of diamond-like carbon (DLC). Even for such a well-studied material as Si, principally new data have been obtained. High spatial resolution of the method allowed us to show that the Raman spectrum that was previously ascribed to a metastable Si-III phase originates from two different high-pressure phases of Si. Up to five different phases of Si were found within a single impression. Studies of reversible transformations that occur upon unloading or heating of samples by the laser beam have also been carried out. Amorphisation and/or phase transformations have been observed for some other materials, such as SiC, quartz, Ge, GaAs and other. The combination of indentation tests with micro-Raman spectroscopy provides a powerful and fast tool for in-situ and ex-situ monitoring of pressure-induced phase transformations in materials. Received: 2 January 1997 / Accepted: March 1997     

Nonstoichiometry and solubility of impurity in In-doped PbTe films on Si substrates

The chemical quantitative composition, phase constitution, and crystal structure of doped with In lead telluride films on Si (1 0 0) or SiO₂/Si (1 0 0) substrates have been studied in this work. By EPMA and atomic absorption measurements, it has been found that the concentration of In atoms y_In varied from 0.0011 to 0.045 in these deposited Pb_1−yIn_yTe films. The results of EPMA, SEM, and X-ray diffraction (XRD) measurements show that formation of In solid solutions in lead telluride matrix revealed not only in PbTe–InTe cross-section, but in PbTe–In₂Te₃ pseudobinary system also. The results of XRD show that the lattice parameter a_PbTe of PbTeIn/Si and PbTeIn/SiO₂/Si heterostructures is described by nonmonotone function and does not obey the Vegard's law within concentration interval 0.0011y_In0.045.     

Mechanical behavior of zirconium dioxide crystals partially stabilized with yttrium oxide

The results are given of a composite investigation of the mechanical behavior of single crystals of zirconium dioxide partially stabilized with yttrium oxide and ytterbium oxide at temperatures up to 1400°C. It is shown that the elastic modulus of these materials lies in the 150–350 GPa range and their tensile strengths may reach 1,688 MPa. These materials have a nonincreasing relationship of the stress intensity factor to crack length (flat R-curves). The stress intensity factors determined on specimens with a sharp crack are significantly lower than on specimens with a notch. The picture of fracture of single crystals in penetration of an indentor, etc. differs significantly in relation to the stabilizing addition.Translated from Problemy Prochnosti, No. 1, pp. 73–77, January, 1991.