Magnetization and initial permeability studies of Nd3+ substituted Zn-Mg ferrite system

Polycrystalline ferrites, Zn _x Mg_1−x Fe_2−y Nd _y O₄ (x=0·00, 0·20, 0·40, 0·60, 0·80 and 1·00;y=0·00, 0·05 and 0·10), were prepared by standard ceramic method. The compositions, on characterization by X-ray diffraction, showed formation of single phase cubic spinels. Magnetic study of the compositions showed increase in magnetic moment,nβ, with Zn²⁺ concentration up tox=0·4 and a decrease thereafter. This was attributed to the existence of canted spin. The compositions forx=0·8 and 1·0 showed paramagnetic behaviour at and above room temperature. The substitution of Nd³⁺ ion caused reduction in the magnetic moment and Curie temperatures. Substituted Nd³⁺ ion showed its occupancy on octahedral (B) site. The dependence of the initial permeability was studied in the temperature range 298 K-700 K. This μ_i-T curve reflects the positive temperature coefficient of initial permeability for the compositionsx≤0·4 andy=0·00. On substitution of Nd³⁺ ion (i.e.y=0·05 and 0·10), the μ_i-T curves flatten, showing almost temperature independence of initial permeability. This is explained by positive contribution to the anisotropy constant,K ₁, by substituted rare-earth, Nd³⁺ ion.     

Growth of Nd<Superscript>3+</Superscript> doped LiNbO<Subscript>3</Subscript> crystals using Bridgman method and its spectral properties

The growth of Nd³⁺ doped lithium niobate crystals using Bridgman method has been reported in this paper. By means of the optimum conditions such as proper feed materials, sealed platinum crucibles, growth rate of 1–1·5 mm/h and temperature gradient of 30–35°C/cm across the solid-liquid interface under the furnace temperature of 1300°C, single crystals containing Nd³⁺ ion with 0·54 mol% concentration were obtained. X-ray diffraction and ICP-AES were used to characterize the crystals and its composition. The absorption, emission and fluorescence lifetime are also measured. Based on the Judd-Ofelt theory, we obtained the optical parameters of the crystal such as the luminescent quantum efficiency, the radioactive lifetimes, the branching ratios and the emission cross-section.     

Phase formation and microstructure of Nd<Superscript>+3</Superscript> doped Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> prepared by sol–gel method

The aim of this study was to investigate the effects of the rare earth element neodymium on the phase formation and microstructural development of relaxor ferroelectric lead magnesium niobate, Pb(Mg_1/3Nb_2/3)O₃ (PMN) system. Perovskite phase PMN powders were prepared using the sol–gel method and the effect of neodymium doping was investigated at different doping levels ranging from 0.1 mol% to 30 mol%. The precursors employed in the sol–gel process were lead (II) acetate, magnesium ethoxide, and niobium (V) ethoxide. All the experiments were performed at room temperature while the calcination temperatures ranged between 800 °C and 1,100 °C. Results showed that it was possible to obtain the pure perovskite phase at 950 °C using the sol–gel method. Nd⁺³ addition influenced the phase formation and microstructure of the multicomponent system. Pyrochlore was detected along with the perovskite phase above 10 mol% Nd. Results also demonstrated that grain size of the synthesized powders depended on the Nd⁺³ concentration.     

Effect of cobalt substitution on magnetic and transport properties of Nd0·5Sr0·5Mn1?xCoxO3 (x = 0·1, 0·3 and 0·5)

The magnetic and transport properties of the compounds Nd_0·5Sr_0·5Mn_1-x_{{\rm 1}-{x}}Co_x_{{x}}O₃ (x = 0·1, 0·3 and 0·5), synthesized by citrate–gel route have been investigated. The spin transition in cobaltates at low temperatures affects the magnetic as well as transport properties. The irreversibility behaviour between the zero-field cooled (ZFC) and field cooled (FC) magnetization as a function of temperature becomes stronger with increasing Co content. This is understood on the basis of glassy behaviour, which becomes more robust with increasing Co substitution. The non-saturating M–H behaviour indicates strong magnetic inhomogeneities which may cause the magnetic phase separation at the nanoscopic length scale. The double exchange interaction is stronger between Mn^3 +–O^2 −–Mn^4 + as compared to Co^3 +–O^2 −–Co^4 + pairs. Co-substitution suppresses the double exchange which will lead to cluster/spin glass like behaviour as well as semiconducting features due to localization of charge carriers (mobile e_g{e}_{\rm g} electrons).     

The effect of manganese oxide on the sinterability of hydroxyapatite

The sinterability of manganese oxide (MnO₂) doped hydroxyapatite (HA) ranging from 0.05 to 1 wt% was investigated. Green samples were prepared and sintered in air at temperatures ranging from 1000 to 1400°C. Sintered bodies were characterized to determine the phase stability, grain size, bulk density, hardness, fracture toughness and Young’s modulus. XRD analysis revealed that the HA phase stability was not disrupted throughout the sintering regime employed. In general, samples containing less than 0.5 wt% MnO₂ and when sintered at lower temperatures exhibited higher mechanical properties than the undoped HA. The study revealed that all the MnO₂-doped HA achieved > 99% relative density when sintered at 1100–1250 °C as compared to the undoped HA which could only attained highest value of 98.9% at 1150 °C. The addition of 0.05 wt% MnO₂ was found to be most beneficial as the samples exhibited the highest hardness of 7.58 GPa and fracture toughness of 1.65 MPam^1/2 as compared to 5.72 GPa and 1.22 MPam^1/2 for the undoped HA when sintered at 1000 °C. Additionally, it was found that the MnO₂-doped samples attained E values above 110 GPa when sintered at temperature as low as 1000 °C if compared to 1050 °C for the undoped HA.     

Investigations on d.c. conductivity behaviour of milled carbon fibre reinforced epoxy graded composites

This paper reports the d.c. conductivity behaviour of milled carbon fibre reinforced polysulphide modified epoxy gradient composites. Milled carbon fibre reinforced composites having 3 vol. % of milled carbon fibre and poly sulphide modified epoxy resin have been developed. D.C. conductivity measurements are conducted on the graded composites by using an Electrometer in the temperature range from 26°C to 150°C. D.C. conductivity increases with the increase of distance in the direction of centrifugal force, which shows the formation of graded structure with the composites. D.C. conductivity increases on increase of milled carbon fibre content from 0·45 to 1·66 vol.%. At 50°C, d.c. conductivity values were 1·85 × 10⁻¹¹, 1·08 × 10⁻¹¹ and 2·16 × 10⁻¹² for samples 1, 2 and 3, respectively. The activation energy values for different composite samples 1, 2 and 3 are 0·489, 0·565 and 0·654 eV, respectively which shows decrease in activation energy with increase of fibre content.     

Pyroelectric properties of Gd-doped KVO3 and LiVO3

Pyroelectric properties of Gd-doped and undoped potassium vanadate and lithium vanadate investigated in the temperature range covering their transition points show sharp increase at Curie temperature for undoped and for 0·025, 0·05, 0·1 mol% Gd₂O₃-doped, but no remarkable peak at Curie temperature for 0·5, 1, 3 mol% Gd₂O₃-doped KVO₃ and LiVO₃. The Curie temperature of all the samples remains the same for various concentrations of Gd.     

Gas sensing performance of nanocrystalline ZnO prepared by a simple route

The nanocrystalline powders of pure and Al³⁺-doped ZnO with hexagonal structure were prepared by a simple hydrothermal decomposition route. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and the microstructure by transmission electron microscopy (TEM). All the compositions exhibited a single phase, suggesting a formation of solid solution between Al₂O₃ and ZnO. DC electrical properties of the prepared nanoparticles were studied by DC conductivity measurements. The indirect heating structure sensors based on pure and doped ZnO as sensitive materials were fabricated on an alumna tube with Au electrodes. Gas-sensing properties of the sensor elements were measured as a function of concentration of dopant, operating temperature and concentrations of the test gases. The pure ZnO exhibited high response to NH₃ gas at an operating temperature of 200 °C. Doping of ZnO with Al³⁺ increased its response towards NH₃ and the Al³⁺-doped ZnO (3.0 wt% Al₂O₃) showed the maximum response at 175 °C. The selectivity of the sensor elements for NH₃ against different reducing gases like LPG, H₂S and H₂ was studied. The results on response and recovery time were also discussed.     

Synthesis, IR, crystallization and dielectric study of (Pb, Sr)TiO 3 borosilicate glass–ceramics

Eleven glass compositions were prepared by melt and quench method with progressive substitution of SrO for PbO (0?≤?x?≤ 1·0) with a step-wise increment of 0·10 in the glass [(Pb _x Sr_1???x )OTiO₂]–[(2SiO₂B₂O₃)]–[BaO·K₂O]·Nb₂O₅ (mol percentage) system. The infrared spectra (IR) of various glass compositions in the above mentioned glass system was recorded over a continuous spectral range 400–4000 cm^???1 to study their different oxides structure systematically. Differential thermal analysis (DTA) was recorded from room temperature (~27 °C) to 1400 °C employing a heating rate of 10 °C /min to determine glass transition temperature, T _g and crystallization temperature, T _c. The melting temperature, T _m, of these glass compositions was found to be in the range 597–1060 °C depending on the composition under normal atmospheric conditions. T _g and T _m of glasses were found to increase with increasing SrO content. X-ray diffraction analysis of these glass–ceramic samples shows that major crystalline phase of the glass–ceramic sample with x ≤ 0·5 was found to have cubic structure similar to SrTiO₃ ceramic. Scanning electron microscopy has been carried out to see the surface morphology of the crystallites dispersed in the glassy matrix.     

Effect of fluxing additive on sintering temperature, microstructure and properties of BaTiO3

Various fluxing materials are added to technical ceramics in an attempt to lower their sintering temperatures and make their processing economical. The effect of 0·3?wt% Li₂CO₃ addition on the phase, microstructure, phase transition temperatures and dielectric properties of BaTiO₃ was investigated in the present study. The addition of 0·3?wt% Li₂CO₃ was observed to lower the optimum sintering temperature by ??200°C with no second phase formation and cause a five-fold reduction in grain size. Rhombohedral-to-orthorhombic and tetragonal-to-cubic phase transitions at the expected temperatures were evident from the Raman spectra, but the orthorhombic-to-tetragonal phase transition was not clearly discernible. The persistence of various phase(s) at higher temperatures in the flux-added materials indicated that the phase transitions occurred relatively slowly. A decrease in dielectric constant of Li₂O-added BaTiO₃ in comparison to pure BaTiO₃ may be due to the diminished dielectric polarizability of Li^?+? in comparison to Ba^2?+?.     

The optical and electrical properties in Nd<Superscript>3+</Superscript> doped lead tungstate single crystals

The influence of Nd³⁺ doping with different concentration on the luminescence properties of PbWO₄ single crystals were investigated by means of the thermo-luminescence, X-ray excited luminescence and photoluminescence spectra. Nd³⁺ doping has almost the same doping effects as that of La³⁺ doping in PbWO₄. The doping mechanism of Nd³⁺ was briefly discussed. Dielectric loss spectroscopy and conductibility were measured when the PbWO₄:Nd³⁺ single crystals were sequentially annealed in air atmosphere from 100 °C to 1000 °C. The heavily Nd³⁺-doped PbWO₄ present a larger conductivity at the high temperature with low activation energy.     

Combustion synthesis and structural characterization of Li–Ti mixed nanoferrites

Polycrystalline samples of the mixed nanoferrites, Li_{0·5 + 0·5x} Ti _x Fe_{2·5 − 1·5x} O₄ (0·02 ≤ x ≤ 0·1), were prepared by combustion method at lower temperatures compared to the conventional high temperature sintering for the first time at low temperatures, using PEG which acts as a new fuel and oxidant. XRD patterns reveal a single-phase cubic spinel structure. The as synthesized Li–Ti ferrites are in nanocrystalline phase. The crystallite size was found to be in the range 16–27 nm. SEM images reveal rod-like morphology in all the samples with a discontinuous grain growth. The B–H loops have been traced using VSM technique, for all the compositions, at room temperature and the hysteresis parameters are calculated. Saturation magnetization decreases with increase in Ti content due to the fact that the Ti^4 + ion, which is a non-magnetic ion, replaces a magnetic Fe^3 + ion. The hysteresis loops show clear saturation at an applied field of ±10 kOe and the loops are highly symmetric in nature. The cation distribution is known indirectly by using saturation magnetization values.     

Dielectric response of PLZT ceramics <Emphasis Type="Italic">x</Emphasis>/57/43 across ferroelectric–paraelectric phase transition

The dielectric properties of lead lanthanum zirconate titanate (PLZT) ceramics [Pb(Zr_0·57Ti_0·43)O₃ + x at% of La, x = 3, 5, 6, 10 and 12] have been measured in the frequency range 1 Hz–1 MHz using the vector impedance spectroscopy (VIS) at different temperatures. All the compositions show both non-dispersive and dispersive dielectric responses in different temperature regions. The non-dispersive region obeys the universal dielectric response. A low frequency (<1 kHz) relaxation phenomenon with a high value of distribution parameter ‘h’ (~0·4 to 0·6) has been observed in all the compositions around the temperature corresponding to the maximum dielectric constant (T _m). The activation energies as calculated from the relaxation and d.c. conduction processes are comparable. The ferroelectric phase transition is diffuse in nature and broadening of the peak increases with La content.     

Composition and concentration dependence of spectroscopic properties of Nd-doped tellurite and metaborate glasses

The spectroscopic properties of tellurite glasses of composition (in mol%) TNKNd: (70 − x)TeO₂-15Nb₂O₅-15K₂O-xNd₂O₃ (x = 0.1, 1.0, 1.5, 2.0 and 2.5) and TNLNd10: 69TeO₂-15Nb₂O₅-15Li₂O-1.0Nd₂O₃ and lithium metaborate glass of composition LBNNd10: 89LiBO₂-10Nb₂O₅-1.0Nd₂O₃ have been investigated using absorption and emission spectra and decay curve analysis. An energy level analysis has been carried out considering the experimental energy positions of the absorption and emission bands, using the free-ion Hamiltonian model. The spectral intensities have been calculated by using the Judd-Ofelt theory and in turn the radiative properties such as radiative transition probabilities, emission cross-sections, branching ratios and radiative lifetimes have been estimated. The decay curves at the lower concentrations are exponential while they show a non-exponential behavior at higher concentrations (?1.0 mol%) due to energy transfer processes. The effective lifetimes for the ⁴F_3/2 level are found to decrease with increase in Nd₂O₃ concentration for all the glasses under investigation. The non-exponential decay curves have been well-fitted to the Yokota-Tanimoto model with S = 6, indicating that the nature of energy transfer is of dipole-dipole type and energy migration also plays an important role. The results obtained have been compared with Nd³⁺-doped phosphate, fluorophosphate, lead borate, tellurite, germanate and silicate glasses and Nd³⁺-doped YAG ceramic and Ca₂Nb₂O₇ crystals.     

Some barium titanate based dielectrics

Some new potential dielectric materials have been made through the cross-substitution of Ba²⁺ by a 1:1 molar combinations of tri-(La³⁺) and mono-valent (Li⁺, Na⁺, K⁺) ions at the Ba²⁺ site in BaTiO₃. Chemical analysis shows that compositions in the potassium series are about 6·1% deficient in their K₂O content and exhibit interesting dielectric relaxations. The cross-substitution has lowered theT _c down to room temperature. The disorder in the larger ‘A’ cation sublattice of the three systems has been established by infra-red and x-ray data. This leads to microscopic compositional variations, which in turn can account for the diffuseness of the dielectric anomalies observed in the barium titanate-rich compositions (0⩽x⩽0·3). since deceased.     

Thermoelectric power in Gd3+-substituted Cu-Cd ferrites

Polycrystalline Cd _x Cu_1−x Fe_2−y Gd _y O₄ ferrites fory=0·0 and 0·1 were prepared by ceramic technique. X-ray diffractograms of powder samples show cubic symmetry withx⩾0·2 fory=0·0 and 0·1, while compositions withx=0·0 fory = 0·0 and 0·1 are tetragonal. The thermopower measurements for Gd³⁺-undoped ferrites in the temperature range 300 K to 788 K shown-type conductivity forx⩾0·2. The substitution of Gd³⁺ changedn-type conductivity of the compositions top-type. The mobilities calculated show decreasing trend on Gd³⁺ substitution. The values of activation energy ΔE and drift mobilityE _d suggest polaron formation in substituted samples. The conduction mechanism is explained on the basis of localized model and formation of Gd³⁺+Fe²⁺ stable pairs at B site and Cu¹⁺+Fe³⁺ at A site.     

Influence of microstructure on dielectric properties of Nd-doped barium titanate synthesized by hydrothermal method

Nd-doped barium titanates were successfully synthesized via a hydrothermal route. The as-prepared barium titanate was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transformation infrared spectroscopy (FTIR), and Vis–NIR spectroscopy respectively. The results show that pure and Nd-doped barium titanate powders have cubic perovskite structure. After sintering at a temperature of 1,250 °C for 2 h, the phase compositions of all barium titanate are tetragonal phase structure. Vis–NIR spectra well confirmed that Nd³⁺ have been doped into barium titanate. The particle diameters of Nd-doped barium titanate powders and ceramics become samller with the increase of Nd³⁺ content. When Nd/Ba molar ratio is 0.02, the dielectric loss (0.0008) of the powder measured at 1 MHz and room temperature dramatically decreases by 99 % comparing with pure barium titanate (0.083) and shows frequency independence with the frequency increasing from 40 Hz to 1 MHz. The dielectric constant and dielectric loss are 436 and 0.09 after sintering. The Nd-doped BaTiO₃ show an improvement in the dielectric quality which possess a decreased sensitivity to frequency for both the dielectric constant and dielectric loss. Such improvements are of potential importance for high energy density and low loss.     

X-ray crystallographic and conductance study of CuNiSnO4 synthesized by two different methods

Two new ternary oxidic compositions of CuNiSnO₄ have been prepared. The ternary composition Cu²⁺Ni²⁺SnO₄ in orthorhombic symmetry with lattice dimensionsa ₀=5·773 ± 0·01 Å;b ₀=8·377 ± 0·01 Å;c ₀=10·094 ± 0·01 Å, while Cu⁺Ni³⁺SnO₄ is also orthorhombic but with lattice dimensionsa ₀=5·737 ± 0·01 Å;b ₀=7·125 ± 0·01 Å andc ₀=10·071 ± 0·01 Å. The variation of electrical conductance with temperature indicates the semiconducting nature of these compositions. Hot-probe method indicatesp-type semiconduction in both the compositions     

Creep of silicon nitride-titanium nitride composites

The effect of particulate TiN additions (0–50 wt%) on creep behaviour of hot-pressed (5 wt%Y₂O₃ + 2 wt%Al₂O₃)-doped silicon nitride (HPSN)-based ceramics was studied. Creep was measured using a four-point bending fixture in air at 1100–1340 °C. At 1100 °C, very low creep rates of HPSN with 0–30 wt% TiN are observed at nominal stresses up to 160 MPa. At 1200 °C the creep rate is slightly higher, and at 1300 °C the creep rate is increased by three orders of magnitude compared to 1100 °C and rupture occurs after a few hours under creep conditions. It was established that the formation of a TiN skeleton could detrimentally affect the creep behaviour of HPSN. An increase in TiN content leads to higher creep rates and to shorter rupture times of the samples. Activation energies of 500–1000 kJ mol^?1 in the temperature range of 1100–1340 °C at 100 MPa, and stress exponentsn?4 in the stress range 100–160 MPa at 1130–1200 °C were calculated. Possible creep mechanisms and the effect of oxidation on creep are discussed.