Formation of secondary phases and microdiscs on flux-grown HoFeO3 crystals

Results of optical and scanning electron microscopic and EDAX studies, carried out on structures exhibited by HoFeO₃ crystals grown from the PbO-PbF₂-B₂O₃ flux system, are reported. Aluminium and silicon are present as impurities in the crystals studied. EDAX of certain structures indicate formation of magnetoplumbite (PbO · 6Fe₂O₃) during the flux growth of HoFeO₃. Crystallization of HoOF on the HoFeO₃ crystal surfaces is also indicated; the process taking place almost at the end of HoFeO₃ crystal growth. A variety of microdisc patterns on HoFeO₃ crystal surfaces are illustrated. Their formation is attributed to the covering process of impurity phases by the rapidly advancing growth fronts on the HoFeO₃ crystal surfaces. Experimental evidence in support of this is offered by exposing the impurity phase buried under the microdisc. Precipitation of the secondary phases during the flux growth of HoFeO₃ crystals and their influence on the latter is discussed.     

Characterization of flux-grown PZN-PT single crystals for high-performance piezo devices

Relaxor ferroelectric Pb(Zn(1/3)Nb(2/3))O(3-x)PbTiO(3) (PZN-PT) and Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3)(PMN-PT) single crystals are the potential candidates for future high-performance piezoelectric devices due to their exceptionally high dielectric and piezoelectric properties. Characterization on flux-grown PZN-PT single crystals of different orientations revealed that PZN-(6-7)%PT single crystals show good homogeneity in dielectric and electromechanical properties and composition. When poled in [001] direction, these crystals exhibit high longitudinal-mode properties with dielectric constant (K(T)) approximately equal to 7000, piezoelectric coefficients (d(33)) approximately equal to 2800 pC/N, and electromechanical coupling factors (k(33)) > or = 0.92. For [011]-cut crystals, optimally poled PZN-7%PT single crystal exhibits very high transverse-mode dielectric and piezoelectric properties with K(T) > or = 5000, d(32) approximately equal to -3800 pC/N and k(32) > or = 0.90. [011]- poled PZN 6%PT has d(32) approximately equal to -3000 pC/N and comparable k(32) and K(T) values. In comparison with melt-grown PMNPT single crystals, flux-grown PZN-PT single crystals show good compositional homogeneity, superior and consistent dielectric and electromechanical properties, and higher depolarization temperatures (TDP).     

Microstructural,etching and hardness studies on flux-grown KNiF3 crystals

Surface structures on {100} faces of flux-grown KNiF₃ crystals are reported. Etching experiments establish HNO₃ to be a dislocation etchant for the crystals. The etching behaviour of the HNO₃-KNiF₃ surface system is investigated. The results obtained on the effect of etching time and etchant concentration on lateral extension and depth of dislocation etch pits are reported. It is observed that the etchant is rendered passive after some period of initial etching. Indentation-induced hardness testing studies suggest a Vickers microhardness value in the range of (2.93 to 3.50)×10² kg mm^–2, and the response of indentation to load is in accordance with Kick's Law.     

Load and directional effects on microhardness and estimation of toughness and brittleness for flux-grown LaBO3 crystals

Results of microhardness measurements on (100) and (110) planes of flux-grown LaBO₃ crystals, in the applied load range of 10–100g, are presented. The microhardness was found to decrease with increasing load in a non-linear manner. By applying Hays and Kendall's law, the materials resistance pressure and other constants of the equation could be calculated. Hardness anisotropy, showing periodic variation of H _v with the maxima and minima repeating at every 15° change in orientation of the indentor, is described and discussed. H _max/H_min are estimated as 1.14 and 1.06 for (100) and (110) planes, respectively. The fracture toughness values, K _c, determined from measurements of crack lengths, are estimated to be 1.6, 1.7 MN m^–3/2 (for (100) planes) and 1.2, 1.5 MN m^–3/2 (for (110) planes) at 90 and 100g loads, respectively. The brittleness index, B _i, is estimated as 4.6, 4.0 m^–1/2 (for (100) planes) 6.0, 4.6 m^–1/2 (for (110) planes) at 90 and 100g, loads respectively.     

Surface structural investigations on (100) and (110) faces of flux-grown lanthanum borate crystals

Results of topographical studies carried out on (100) and (110) faces of lanthanum borate crystals grown from the PbO-B₂O₃ flux system are illustrated and discussed. The habit faces display the formation of cavities, microcrystals, elliptical etch pits, elliptical hillocks, circular hillocks and irregular structures. Also described are a various number of elevated structures identified as impurity phases. Energy dispersive X-ray (EDAX) studies have confirmed that these impurity phases in the growth of lanthanum borate (LaBO₃) crystals are enriched by lead (Pb). The habit faces also exhibit some elevated regions which are reported to be more imperfect in comparison with others. It is inferred that independent growth on the habit faces has taken place during the last stage of crystal growth by a two-dimensional nucleation mechanism.     

Microhardness measurements on single crystals of flux-grown rare earth perovskites (orthoferrites,orthochromites and aluminates)

The results of indentation-induced microhardness testing studies of flux-grown single crystals of rare earth orthoferrites, RFeO₃ (R=Gd to Er and Yb), rare earth orthochromites RCrO₃ (R=La, Eu and Dy), and rare earth aluminates RAlO₃ (R=La, Sm, Gd, Eu and Ho) are presented. The variation in the value of microhardness with load is observed to be non-linear in the case of all these materials. It is found that the results are not in accordance with Kick's law. The results have been analysed and the applicability of the idea of materials resistance pressure in the modified law as proposed by Hays and Kendall [Metallography 6 (1973) 275] is discussed.     

Optical and scanning electron microscopic and energy-dispersive X-ray analytical studies on some typical surface structures of flux-grown DyFeO3 crystals

The results of optical, scanning electron microscope and qualitative analysis studies conducted on surface structures displayed by flux-grown DyFeO₃ crystals are reported. The crystals were grown from PbO-PbF₂ B₂O₃ flux under various conditions. Magnetoplumbite (PbO · 6Fe₂O₃) is the most favoured secondary phase. Crystallization of DyOF and DyBO₃ on the DyFeO₃ crystal surfaces also takes place, almost at the end of DyFeO₃ crystal growth. Macro- and micro-disc patterns on DyFeO₃ and a rare observation of an elliptical disc of material containing lead are illustrated. Metallic platinum deposited on flux-grown DyFeO₃ is reported when the crystals were finally cooled in contact with the flux. Additional secondary phases (material containing lead, platinum, PbO · 6Fe₂O₃, DyBO₃) and other imperfections (inclusions, cavities, microcrystals) also occur. The addition of V₂O₅ to the flux leads to incorporation of traces of vanadium in the DyFeO₃ crystals and DYVO₄ as a secondary phase.     

Lattice disorder and electrical conductivity of flux-grown Ca(WO4) x (MoO4)1−x crystals

The growth of solid solutions of Ca(WO₄) _x (MoO₄)_1–x in the rangeX=0.072 to 0.86 has been successfully accomplished for the first time, employing a flux technique. The fact that proper mixing occurs is established by observing the variation in unit cell parameters and density of the crystals. The electrical conductivity of the pelletized samples is interpreted in terms of Schottky and Frenkel defect concentrations. The role of oxygen ion vacancies is stressed for the intrinsic region of conductivity.     

Spontaneous emission and lame shift in photonic crystals

Being motivated by the controversial results based on two dispersion models and Weisskopf–Wigner approximation (WWA), we introduce, for the first time to our knowledge, the position-dependent photon-atom interaction into the Green function method of the evolution operator and develop a universal theoretical approach to study spontaneous emission of atoms in photonic crystals (PCs). A position-sensitive generalized Lorentzian formalism (non-Lorentzian shape) for the decay of an excited atom in PCs is derived, and an exact numerical method for calculating the local coupling strength, proportional to the photonic local density of state (LDOS), is presented. For weak interaction PCs with pseudo gaps, the generalized Lorentzian formalism may be reduced to the famous Lorentzian spectrum. In this case, we introduce a lifetime distribution function for an assembly of atoms and find that it depends strongly on the atomic configuration in space, which clarifies successfully the tremendous discrepancy between different experiments. For the PCs with large full gaps, we find that the atomic position can fundamentally change the decay behavior of an excited atom: in strong interaction positions, the atomic decay is non-classical or exhibits an envelope-damped Rabi oscillation, while in weak interaction positions the WWA is valid. Recently, we also predicted giant Lamb shifts for hydrogen atoms in PCs, and revealed that in inhomogeneous electromagnetic environment, the dominant contribution to the Lamb shift comes from real photon emission, while the contribution from emission and reabsorption of virtual photon is negligible, in vast contrast with the case of free space where the virtual photon processes play a key role.     

Exoelectron emission and critical phenomena in CuCl crystals

The temperature dependence of thermostimulated exoelectron emission (TSEE) and the specific heat c _p of CuCl single crystals were studied in a broad temperature range. It is suggested that the TSEE peaks observed in the region of 375 and 420°C are due to the polytype formation and the structural transition from a sphalerite to wurtzite polymorph; the peak at 170°C is assigned to Cu²⁺ ions present in the CuCl crystals studied.     

Influence of Na deposition on convoy-electron emission

The influence of surface properties on convoy-electron emission from a sputter-clean Al foil induced by H⁺ has been studied under ultrahigh-vacuum conditions. It is found that the convoy-electron yield depends strongly on the Na coverage when the downstream surface is modified by controlled Na deposition. It can be concluded that an increasing yield is observed for larger work-function values.     

Glow discharge optical emission spectroscopy for accurate and well resolved analysis of coatings and thin films

In the last years, glow discharge optical emission spectrometry (GDOES) gained more and more acceptance in the analysis of functional coatings. GDOES thereby represents an interesting alternative to common depth profiling techniques like AES and SIMS, based on its unique combination of high erosion rates and erosion depths, sensitivity, analysis of nonconductive layers and easy quantification even for light elements such as C, N, O and H. Starting with the fundamentals of GDOES, a short overview on new developments in instrument design for accurate and well resolved thin film analyses is presented.The article focuses on the analytical capabilities of glow discharge optical emission spectrometry in the analysis of metallic coatings and thin films. Results illustrating the high depth resolution, confirmation of stoichiometry, the detection of light elements in coatings as well as contamination on the surface or interfaces will be demonstrated by measurements of: a multilayer system Cr/Ti on silicon, interface contamination on silicon during deposition of aluminum, Al₂O₃-nanoparticle containing conversion coatings on zinc for corrosion resistance, Ti₃SiC₂ MAX-phase coatings by pulsed laser deposition and hydrogen detection in a V/Fe multilayer system. The selected examples illustrate that GDOES can be successfully adopted as an analytical tool in the development of new materials and coatings. A discussion of the results as well as of the limitations of GDOES is presented.     

Anisotropy of secondary ion emission from single crystals

The fact that secondary ion emission (SIE) exhibits some features in case of single crystal bombardment should be taken into account when secondary ions are used to diagnose the surfaces of various substances. The features are most noticeable in the space and energy distributions of secondary ions and in the dependence of the SIE yield on the direction of primary ion incidence (the orientation effect).     

Thermostimulated exoelectron emission from uranium-activated LiF and NaF crystals

New high-temperature peaks of thermostimulated exoelectron emission (TSEE) from uranium-activated LiF and NaF Crystals were observed. TSEE parameters for various (Li,Na)-(U+Me) systems were determined.