Growth, thermal and spectral properties of Nd-doped NaGd(MoO4)2 crystal

Nd³⁺-doped NaGd(MoO₄)₂ crystal with dimensions were grown by Czochralski method. Nd³⁺:NaGd(MoO₄)₂ crystal melts at 1182 °C. The hardness of Nd³⁺:NaGd(MoO₄)₂ crystal is 334 VDH. The specific heat is 72.6 cal/mol K. The thermal expansion coefficients are for c-axis and for a-axis, respectively. The absorption cross-sections of Nd³⁺:NaGd(MoO₄)₂ crystal are with a FWHM of 9 nm at the 804 nm for π-polarization and with a FWHM of 17 nm at 807 nm for σ-polarization, respectively. The emission cross-section σ_em are at 1063 nm for π-polarization and 1.94×10^-20 at 1070 nm cm² for σ-polarization, respectively. The fluorescence lifetime τ_f is 93.9 μs at room temperature.     

Growth and characterization of nonlinear optical single crystals of l-arginine diiodate

Growth of good optical quality single crystals of l-arginine diiodate (abbreviated as LADI), a semiorganic nonlinear optical (NLO) material is reported. Crystals of dimension up to were obtained from its aqueous solution by slow solvent evaporation technique. The crystals were characterized by single crystal XRD, FTIR, optical absorption spectrum, microhardness, dielectric and photoconductivity studies. The DTA and TGA traces of LADI confirm the decomposition of the sample at 145 °C.     

Growth of cubic silicon carbide on oxide using polysilicon as a seed layer for micro-electro-mechanical machine applications

The growth of highly oriented 3C–SiC directly on an oxide release layer, composed of a 20-nm-thick poly-Si seed layer and a 550-nm-thick thermally deposited oxide on a (1 1 1)Si substrate, was investigated as an alternative to using silicon-on-insulator (SOI) substrates for freestanding SiC films for MEMS applications. The resulting SiC film was characterized by X-ray diffraction (XRD) with the X-ray rocking curve of the (1 1 1) diffraction peak displaying a FWHM of 0.115° (414″), which was better than that for 3C–SiC films grown directly on (1 1 1)Si during the same deposition process. However, the XRD peak amplitude for the 3C–SiC film on the poly-Si seed layer was much less than for the (1 1 1)Si control substrate, due to slight in-plane misorientations in the film. Surprisingly, the film was solely composed of (1 1 1) 3C–SiC grains and possessed no 3C–SiC grains oriented along the 3 1 1 and 1 1 0 directions which were the original directions of the poly-Si seed layer. With this new process, MEMS structures such as cantilevers and membranes can be easily released leaving behind high-quality 3C–SiC structures.     

Heteroepitaxial growth of Cu2O thin film on ZnO by metal organic chemical vapor deposition

Cuprous oxide (Cu₂O) thin films were grown epitaxially on c-axis-oriented polycrystalline zinc oxide (ZnO) thin films by low-pressure metal organic chemical vapor deposition (MOCVD) from Copper(II) hexafluoroacetylacetonate [Cu(C₅HF₆O₂)₂] at various substrate temperatures, between 250 and 400 °C, and pressures, between 0.6 and 2.1 Torr. Polycrystalline thin films of Cu₂O grow as single phase with [1 1 0] axis aligned perpendicular to the ZnO surface and with in-plane rotational alignment due to (2 2 0)_Cu2O(0 0 0 2)_ZnO; [0 0 1]_Cu2O[1 2¯ 1 0]_ZnO epitaxy. The resulting interface is rectifying and may be suitable for oxide-based p–n junction solar cells or diodes.     

The fabrication and properties of solid polymer electrolytes based on PEO/PVP blends

New solid polymer electrolytes were fabricated by the addition of lithium perchlorates in the blends of polyethylene oxide (PEO, MW = 5 × 10⁶) and poly-4-vinylpyridine (PVP, MW = 1.6 × 10⁶). Not only the coordinating bonding between ether units (-O-) of PEO and Li⁺ ions at about 1100 cm⁻¹ but also the existence of pyridine salts at about 3500 cm⁻¹ were definitely observed in the FT-IR spectra. The addition of PVP in the PEO matrix is to restrict mobility of ions through the coupling of PVP and ions. Therefore, the increase of PVP content is expected to decrease the self-discharge rate. In the case of PEO-PVP blends without LiClO₄, the melting temperature T_m and the degree of crystallinity were decreased by the increase of PVP content. On the contrary, those of PEO-PVP blends with LiClO₄ were increased with the increase of PVP content. The results can be explained lay ions, which reduced the crystallinity of PEO by steric hindrance, segregated from the PEO by the coupling of PVP and ions. The new solid polymer electrolytes based on PEO-PVP blends showed ionic conductivities of the order of 10⁻⁸ to 10⁻⁷ S/cm.     

A combined measurement of thermal and mechanical relaxation

In order to describe relaxation the thermodynamic coefficient can be generalized into a complex frequency-dependent cross response function. We explore theoretically the possibility of measuring for a supercooled liquid near the glass transition. This is done by placing a thermistor in the middle of the liquid which itself is contained in a spherical piezoelectric shell. The piezoelectric voltage response to a thermal power generated in the thermistor is found to be proportional to but factors pertaining to heat diffusion and adiabatic compressibility κ_S(ω) do also intervene. We estimate a measurable piezoelectric voltage of 1 mV to be generated at 1 Hz for a heating power of 0.3 mW. Together with κ_S(ω) and the longitudinal specific heat c_l(ω) which may also be found in the same setup a complete triple of thermoviscoelastic response functions may be determined when supplemented with shear modulus data.     

Effect of heat-treatment condition on crystallization behavior and thermal expansion coefficient of Li2O-ZnO-Al2O3-SiO2-P2O5 glass-ceramics

Utilizing P₂O₅ as nucleation agent, a Li₂O-ZnO-Al₂O₃-SiO₂ glass was prepared by conventional melt quenching technique and subsequently converted to glass-ceramics with different crystal phases. During the processing, two-step heat-treatments including nucleation and crystallization were adopted. The effects of heat-treatment on the crystal type, the microstructure and the thermal expansion behavior of the glass-ceramics were studied by means of differential scanning calorimetry, X-ray powder diffraction analysis, scanning electron microscopy and thermal expansion coefficient tests. It was shown that the crystallization of occurred after the glass was treated at 580 °C. As the temperature increased from 580 °C to 630 °C, cristobalite and were identified as main and second crystal phases, respectively, in the glass-ceramic. An increase in the temperature to 700 °C, the β-quartz solid solution in the glass-ceramic accompanied by a decrease in cristobalite content. The transformation from to γ₀-Li₂ZnSiO₄ took place from 700 °C to 750 °C. The resulting crystallization phases in the glass-ceramics obtained at the temperature higher than 750 °C were β-quartz solid solution and γ₀-Li₂ZnSiO₄. The glass-ceramics containing or β-quartz solid solution crystal phase possessed a microstructure formed by the development of dendritic crystals. The thermal expansion coefficient of the glass-ceramics varied from 36.7 to 123.8 × 10⁻⁷ °C⁻¹ in the temperature range of 20-400 °C, this precise value is dependent on the type and the proportion of the crystalline phases presented.     

Effect of silver doping on the structure and phase separation of sulfur-rich As–S glasses: Raman and SEM studies

We report on the structural details and microphase separation of the bulk glasses Ag_x·(As₃₃S₆₇)_100-x for 0x25. Glass–glass phase separation occurs over a wide range of Ag content, i.e. 4x20. An off-resonant polarized Raman spectroscopic study has been carried out to elucidate structural aspects at the short- and medium-range structural order of the glasses. Analysis of Raman spectra revealed quantitative changes of the sulfur-rich microenvironments that reduce upon adding Ag. Scanning electron microscopy combined with X-rays microanalysis have been utilized to examine the type and extent of phase separation, and to provide quantitative details on the atomic concentrations in the Ag-poor and Ag-rich phases. It has been shown that at 7 at.% Ag the Ag-rich phase percolates through the structure; this effect can be associated with an ionic-to-superionic behavior of these glasses in accordance with similar studies on the stoichiometric arsenic sulfide glass; although the phase separation observed in the present glasses is qualitatively different.     

Interrelation between the parameters of equations of viscous flow and chemical composition of glassforming melts

The number of free parameters of viscosity equations are reduced to two by assuming that the glass transition temperature T_g is the temperature at which viscosity is 10^13.5 [dPa s]. In this way the Avramov and Milchev AM equation is becoming while the VFT equation is transformed to the form: . It is demonstrated that the dimensionless fragility parameter a of the AM equation depends on composition, x, as α = α_ο + 6x, where α_ο = 1 − 2 for silicates and α_ο = 2.75 for borates. We show that the fitting parameters of AM and of VFT equations are correlated. Thus the relationship between the pre-exponential constants is lg η_V ≈ lg η_A − 2. There is also relationship between the fragility parameter a and the divergence temperature T_o of the VFT equation.We develop an alternative approach to consider the vibration frequency of building units of the system. The superposition of the independent vibrations of the atoms constituting the building unit causes a “beat” of the latter.