H. N. Acharya

Monophasic silica glasses with large neodymia concentration

Abstract The use of one ideal candidate for high-powered lasers, neodymia-silica glass, is unfortunately limited by phase separation into undesirable Nd-rich crystalline droplets within an Nd-deficient matrix. Plasma CVD and sol-gel process using NdCl3 or Nd(NO3)3 as dopant both failed to produce single-phase Nd2O3SiO2 glass when neodymia exceeded 5 wt%. Using Nd(COOCH3)3 and acetic acid hydrolysed tetraethyl orthosilicate, the present authors produced monolithic glasses 10 (wt%) Nd2O3 · 90 SiO2 with no observable phase separation. Nd chloride doped gels, where the neodymium concentration increased from the interior to the surface, were much poorer in chemical homogeneity than Nd acetate doped gels of equivalent composition. Free salts of neodymium are responsible for causing the concentration gradient.

Structural and dielectric properties of Nd modified Pb(Zr0.60Ti0.40)O3 ceramics

Abstract Ferroelectric Pb1−zNdz(Zr0.60Ti0.40)1−z/4O3 (z=0.07, 0.08, 0.10) (PNZT) fine powders have been prepared through the acetate alkoxide sol–gel techniques. XRD and TEM studies indicate that the PNZT powders can be formed at 550°C in the perovskite structure. The pellet samples (sintered at 1300°C for 7 h) prepared from the above powders have high density. SEM study shows the uniform distribution of spherical grains throughout the sample surface. Studies of dielectric and electrical properties show that PNZT has diffuse phase transition of second order.

X-ray, SEM and dielectric studies of Gd-modified sol–gel-prepared lead zirconate–lead titanate solid solution

Abstract Polycrystalline samples of (Pb 1− z Gd z )(Zr 0.60 Ti 0.40 ) 1− z /4 O 3 ( z =0.07, 0.08, 0.10) have been synthesized by an acetate–alkoxide sol–gel process. X-ray diffraction analysis suggests the formation of a single-phase material. The scanning electron microscopy (SEM) study shows the uniform distribution of grains in the samples. Detailed dielectric studies of the compounds, as a function of temperature (from 30°C to 450°C) at 10 3 Hz and 10 4 Hz, show that the compounds undergo a diffuse phase transition. Diffusivity ( γ ) study of phase transition of these compounds provides its value between 1 and 2, indicating the variation of degree of disordering in the system. The value of remanent polarization and coercive field decrease with increase of Gd ion concentration.

Characterizations of sol-gel grown (PbLaLi)(Zr0.60Ti0.40)O3

Polycrystalline samples of Pb0.92(La1−zLiz)0.08(Zr0.60Ti0.40)0.98+0.04zO3 (z=0.0, 0.1, 0.3, 0.5, 0.7) have been prepared using the metal-alkoxide sol-gel technique. Differential thermal analysis and x-ray diffraction studies show that the above materials can be formed in a single-phase perovskite structure at 550 °C. The formation of grain structure, particle size, and their distributions have been studied by scanning electron microscopy and transmission electron microscopy, respectively. Systematic studies of compositional dependence of ferroelectric properties [dielectric constant (e), dielectric loss (tan δ), remanent polarization (Pr), coercive field (Ec), piezoelectric coefficients, and pyroelectric coefficient (pT)] of the compounds have been done. High value of dielectric constant ∼104, remanent polarization (14–24 μC cm−2), pyroelectric coefficient (46–57 nC cm−2 K−1) and small piezoelectric parameters have been observed for all the compounds with z=0.0, 0.1, 0.3, 0.5, and 0.7. The coercive field ...

Effect of Er doping on structural and dielectric properties of sol-gel prepared PZT ceramics

Abstract The polycrystalline complex compounds of (Pb z Er 1−z )(Zr 0.60 Ti 0.40 ) 1−z/4 O 3 (z = 0.07, 0.08, 0.10) (PEZT) were synthesized using the metal–alkoxide sol-gel technique. Powder X-ray diffraction (XRD) studies of these compounds suggest that they can be formed in single-phase perovskite structure by a one-step process at a relatively low temperature. Scanning electron microscopy (SEM) analysis shows that the grains are nearly spherical and distributed uniformly in the compounds. Detailed studies of dielectric properties (ϵ, tanδ, and σ) of the compounds as a function of temperature show a broadening of the permittivity peak and a change in transition temperature with the increase of Er 3+ concentration. Analysis of the diffusivity (γ) of the peaks in these compounds provides a value between 1 and 2. The higher value of γ indicates the greater disordering of the system. The hysteresis loop study confirms the phase transition of the system is of second order.

Characterization of chemically deposited Pb1−xCdxS films by scanning electron microscopy

Etude par microscopie electronique a balayage des structures de surface des couches deposees

Microstructure and electrical characterisations of K-modified PLZT

Potassium-modified PLZT [Pb0.92(La1 − zKz)0.08(Zr0.60Ti0.40)0.98 + 0.04zO3 (z = 0.0, 0.1, 0.3, 0.5, 0.7)] ceramics were synthesised using sol-gel technique. Preliminary structural and microstructural parameters were determined using XRD, SEM and TEM techniques. Detailed studies of dielectric properties at 10 kHz in a wide temperature range suggest that the compounds have diffuse phase transition of second order. Studies of spontaneous polarisation, pyroelectric and piezoelectric properties yielded data for devices.

Preparation and characterisation of monolithic Pr-doped silica glasses by a sol–gel method

Abstract Pr–Al co-doped silica glasses have been prepared using Pr(NO 3 ) 3 6H 2 O, Al(NO 3 ) 3 9H 2 O and a sol of fumed silica and HNO 3 acidified Si(OC 2 H 5 ) 4 as starting materials. The glasses were characterised by density, transmission electron microscope (TEM), EDAX, refractive index, linear shrinkage, absorption and fluorescence spectra. The glasses were also examined in relation to total –OH content with Pr-concentration. Aluminium co-doping modifies the optical properties of the Pr-doped glasses.

Studies on Nd-doped colloidopolymeric silica xerogel

Abstract Neodymia—silica laser glasses with homogeneously dispersed neodymia have been developed using neodymium acetate and a sol of fumed silica and CH 3 COOH acidified TEOS as precursors. The ease of preparation of bulk glasses with lower hydroxyl content makes the colloido-polymeric (hybrid) route attractive. Density, TEM, SEM-EDAX, refractive index and fluorescence studies all point to the fact that the solubility of neodymium in silica is influenced by the nature of the anionic species of the neodymium precursor and the relative amount of TEOS-derived silica in the total silica content of the hybrid gel.

Sol-gel synthesis of Pr-doped silica glasses

Abstract Pr-doped silica gels with Pr-content up to 10 wt.% have been prepared using a colloidal—polymeric as well as polymeric sol-gel method. The gels densified at 1150°C show absorption and fluorescence spectra similar to that of melt or CVD prepared Pr-doped silica glasses. Structural properties of the densified gels have also been studied. Al co-doping increases the fluorescence intensitiy of Pr3+ ions and shifts the maxima to the shorter wavelength side.