Search

The K3Bi2 (PO4)3 (abbreviated as KBPO3) ceramic materials is prepared by solid state reaction method. The Calcination is done at 600°C temperature for 20 hours with intermediate grinding. The structural property of calcined sample is studied by X - ray diffraction technique at room temperature in the 2θ range from 10o to 80o. The phase of the compositions is compared with reported data for ICSD #409582 for KBPO3. The XRD results of sample show no secondary peaks and it confirms the formation of single phase. The pellets are sintered at temperature 620°C respectively for 3 hours. The surface morphology of the sample is studied with Scanning electron Microscopy. The densities of the sintered ceramics are measured by Archimedes Principle. The temperature and frequency variation impedance of KBPO3 is studied. The impedance of the sample shows temperature dependent non-Debye relaxation.

Bulk and nanosized pyrochlore materials Ln{sub 2}ZrTiO{sub 7} (Ln=La, Eu, Dy, Gd and Sm) have been prepared by the sol-gel method. All the samples were characterized by powder X-ray diffraction, Raman and X-ray photoelectron spectroscopy. Magnetic susceptibility ({chi}) measurements of Gd{sub 2}ZrTiO{sub 7}, Sm{sub 2}ZrTiO{sub 7} and Eu{sub 2}ZrTiO{sub 7} were carried out by vibrating sample magnetometer in the temperature range 2-320 K. The variation of {chi}{sup -1} (or {chi}) with temperature of Gd{sub 2}ZrTiO{sub 7}, Sm{sub 2}ZrTiO{sub 7} and Eu{sub 2}ZrTiO{sub 7} follows the Curie law, intermediate formula and the Curie-Weiss law, respectively. From the linear portion of {chi}T vs. T{sup -1} plot of Eu{sub 2}ZrTiO{sub 7} from 2 to 15 K, the classical nearest neighbor exchange (J{sup cl}) and dipolar interactions (D{sub nn}) are obtained. The XPS of Ln{sub 2}ZrTiO{sub 7} (Ln=La, Eu, Dy and Gd) gave characteristic peaks for Ln, Ti, Zr and O. The satellite peaks are observed only for 3d La of La{sub 2}ZrTiO{sub 7}. -- Graphical abstract: Sm{sub 2}ZrTiO{sub 7} does not follow the Curie or the Curie-Weiss law. The effective magnetic moment is found to be 0.768 BM (at 300 K), which is smaller than the free ion moment 1.3-1.4 BM. Display Omittedmore » Research Highlights: {yields} Bulk and nano Ln{sub 2}ZrTiO{sub 7} (Ln=La, Eu, Dy, Gd and Sm) have been prepared by the sol-gel method. {yields} The broad Raman lines are attributed to cation disorder and small crystallite size. {yields} XPS of Ln{sub 2}ZrTiO{sub 7} exhibit characteristic X-ray photoelectron spectral features. {yields} Magnetic moment of Gd{sub 2}ZrTiO{sub 7} is obtained from magnetic susceptibility and ESR spectra.« less

A solid state metathesis approach has been applied to synthesize perovskite oxides such as BaTiO3, PbTiO3, K0.5Bi0.5TiO3 and Na0.5Bi0.5TiO3, these were characterized by powder XRD, IR and energy dispersive spectra (EDS). Potassium titanium oxalate and metal chlorides are used as the starting materials. X-ray analysis shows the formation of a single phase with tetragonal structure for BaTiO3, PbTiO3, K0.5Bi0.5TiO3 and a monoclinic structure for Na0.5Bi0.5TiO3. The Infrared spectra of these compounds show the characteristic band due to Ti–O octahedron for all the compounds. The EDS spectra show the relative ratio of the metal ions. The morphology of synthesized compounds was obtained from SEM measurements.

Indium borate and rare earth substituted indium borates (In(1-x)Ln(x)BO(3) (x=0.0 and 0.05; Ln=Gd, Eu, Dy and Sm)) are prepared at low temperature by metathesis reaction using InCl(3), LnCl(3) and NaBO(2). They are characterized by powder XRD and infrared spectroscopy. All the compositions (In(1-x)Ln(x)BO(3)) crystallize in hexagonal lattice with calcite structure. These borates gave characteristic IR vibrations of planar BO(3) group. Spin-Hamiltonian parameters for Gd(3+) are deduced from room temperature electron spin resonance spectrum of In(0.95)Gd(0.05)BO(3). The electron spin resonance spectrum of In(0.95)Gd(0.05)BO(3) gave several anisotropic lines with g2.0. The ESR spectrum of the sample belongs to the "intermediate" category with 1/4H(CF)/hnu1. The local symmetry of Eu(3+) in In(0.95)Eu(0.05)BO(3) is obtained from its emission spectrum. The R/O ratio of In(0.95)Eu(0.05)BO(3) suggests the occupation of In(3+) site by Eu(3+) with near symmetric octahedral geometry.

Nasicon type compositions Mn0.5MSb(PO4)3 (M = Al, Fe and Cr) are prepared by solid state method. All the compounds are characterized by powder X-ray diffraction, infrared, Raman and electron spin resonance techniques. The crystal structures of these materials are refined by Rietveld and least square minimization programs using X-ray powder diffraction data. Among these compounds, Mn0.5AlSb(PO4)3 and Mn0.5FeSb(PO4)3 crystallize in rhombohedral lattice with R 3 ¯ c and R 3 ¯ space group respectively, while Mn0.5CrSb(PO4)3 adopts monoclinic lattice with P21/n space group. The 31P-MAS nuclear magnetic resonance spectrum of Mn0.5AlSb(PO4)3 indicates only one type of phosphorous in the rhombohedral lattice. All the compounds exhibit characteristic PO4 vibrational bands in infrared and Raman spectra. The room temperature powder electron spin resonance spectra of these samples gave broad signal at g ≈ 2.0 for Mn2+. Frequency dependent impedance measurements are carried out. The thermal expansion of these samples is studied in the temperature range 30–500 °C and they exhibit near zero thermal expansion coefficients.

Zinc bismuth borate glasses with composition 10ZnO–xBi2O3–(90 − x)B2O3 (where x is in mol%, ranging from 25 to 50 in steps of 5) have been prepared using conventional melt quenching technique. Differential scanning calorimetry (DSC) studies showed that the glass transition temperature (Tg) decreases from 473 °C to 449 °C as the content of Bi2O3 increases. The optical absorption studies revealed that the cutoff wavelength increases while optical band gap energy (Eopt) and Urbach energy (ΔE) decreases with increase of Bi2O3 content. The Eopt values of these glasses are found to be in the range 3.464–3.169 eV where as the values of ΔE lies in the range 0.503–0.178 eV. The DSC and optical absorption studies revealed that the glass network becomes less tightly packed and degree of disorder increases with increase in Bi2O3 concentration in the present glass system. The IR studies indicate that these glasses are made up of [BiO6], [BO3] and [BO4] basic structural units. The values of optical basicity evaluated using oxide ion polarizability α b 2 − ( E opt ) obtained from optical band gap are in agreement with those values calculated from optical basicity values of the constituent oxides.

With a view to understand the magnetic and electrical behavior of monovalent substituted lanthanum manganites, a series of materials were prepared by sol–gel route by sintering at 1200 °C. The X-ray diffraction data were analyzed using Rietveld refinement technique and it has been found that all the samples were found to crystallize into rhombohedral structure with R3¯c space group. The values of ferro to paramagnetic (TC) and metal–insulator transition (TP) temperatures were obtained using ac susceptibility and electrical resistivity data, respectively. It has been found that sodium-, potassium- and rubidium-doped samples exhibit two peaks in the electrical resistivity vs. temperature plots. The observed behavior has been explained on the basis of oxygen deficiency present in the samples. The electrical resistivity data were analyzed using various theoretical models and it has been concluded that the electrical resistivity data in the low-temperature regime (T TP) were explained using variable range and small polaron hopping mechanisms.

Rare earth (Eu3+)-doped transition metal borate of compositions Cr1−xEuxBO3 (x = 0, 0.01 and 0.05) have been prepared by B2O3 flux method in ultra pure form. All compositions are characterized by powder XRD and crystallized in hexagonal lattice with space group R 3 ¯ c . IR spectra show characteristic planar BO3 vibrational bands. The diffuse reflectance spectra (DRS) are consistent with ligand to metal ion charge transfer and octahedral symmetry around Cr3+ ion. From the observed band positions, the crystal field parameter Dq and Racah interelectronic repulsion parameters B and C are calculated. From the excitation spectrum of Cr0.95Eu0.05BO3, the phonon energy and electron–phonon-coupling strength are obtained. Its emission spectrum has two intense transitions corresponding to 5D0 → 7F2 at 614 nm in the red and 5D0 → 7F1 at 592 nm in orange regions.

The electrical conductivity of cobalt and titanium substituted barium hexagonal ferrites of different compositions has been investigated as a function of composition and temperature. Plots of log( σT ) versus 10 3 / T are almost linear and show a transition near the Curie temperature. The activation energy in the ferrimagnetic region is in general less than that in the paramagnetic region. An attempt is made to explain the conduction mechanism in Ba–Co–Ti ferrites.

The compound CaTiFeP3O12 has been converted to HxCaTiFe1−x3+Fex2+P3O12 by reduction using hydrogen. The reduced product is characterized by powder X-ray diffraction (XRD) and Mossbauer spectroscopy and its unit cell parameters are deduced. Mossbauer spectral results suggest that CaTiFeP3O12 could not be reduced completely. The effect of heat treatment on the reduced product has been studied.

Rare earth zirconium oxides of compositions La2Zr2O7 and Nd2Zr2O7 were prepared by sol–gel method. They were characterized by IR spectra and powder X-ray diffractograms. Nano-sized and bulk particles of La2Zr2O7 and Nd2Zr2O7 were obtained at 500 and above 800 °C, respectively. The particle size was found to increase with increase in the sintering temperature.

New sodium super ionic conductor NASICON type niobium aluminum phosphates of composition Cu NbAlP O 0.5 3 12 . . CNP and HNbAlP O HNP are prepared. The compounds are isomorphous with NbTiP O and unit cell parameters are 31 2 31 2 . evaluated. Copper and hydrogen occupy the channels. Reduction of CNP gives rise to HNP. electron spin resonance ESR . 2q and photo acoustic PA spectral data are consistent with elongated octahedral configuration around Cu ion. q 2000 Elsevier Science B.V. All rights reserved.

The title compounds are prepared by the sol—gel method starting with Ln2O3 dissolved in HNO3, aqueous solutions of ZrO(NO3)2, and H2O2 solutions containing Ti powder and NH3 followed by heating of the obtained precursors (500—900 °C, 5 h).

Nasicon type compositions Mn0.5MSb(PO4)3 (M = Al, Fe and Cr) are prepared by solid state method. All the compounds are characterized by powder X-ray diffraction, infrared, Raman and electron spin resonance techniques. The crystal structures of these materials are refined by Rietveld and least square minimization programs using X-ray powder diffraction data. Among these compounds, Mn0.5AlSb(PO4)3 and Mn0.5FeSb(PO4)3 crystallize in rhombohedral lattice with R 3 ¯ c and R 3 ¯ space group respectively, while Mn0.5CrSb(PO4)3 adopts monoclinic lattice with P21/n space group. The 31P-MAS nuclear magnetic resonance spectrum of Mn0.5AlSb(PO4)3 indicates only one type of phosphorous in the rhombohedral lattice. All the compounds exhibit characteristic PO4 vibrational bands in infrared and Raman spectra. The room temperature powder electron spin resonance spectra of these samples gave broad signal at g ≈ 2.0 for Mn2+. Frequency dependent impedance measurements are carried out. The thermal expansion of these samples is studied in the temperature range 30–500 °C and they exhibit near zero thermal expansion coefficients.

Lithium containing sodium superionic conductors of composition LiSbM(PO4)3 (M=Al, Cr, and Fe) were prepared by solid-state method and were characterized by powder x-ray diffraction and infrared spectroscopy. All compounds were found to crystallize in rhombohedral lattice with space group R3¯c. They show characteristic PO4 vibrational bands. The dc conductivity and ac impedance studies of all these samples correlate well in terms of activation energy of conduction Ea. The Cole-Cole plots do not show any spikes on the lower frequency side, indicating negligible electrode effects. The activation energies obtained from the plots of logσdc vs 1∕T and logσ(0) vs 1∕T are approximately the same suggesting conducting species to be mobile lithium ions. The peak width at half maximum for modulus plots (logf vs M″) is ∼1.34 decades for LiSbM(PO4)3 (M=Al, Cr, and Fe), which is close to 1.14 decades observed for a Debye solid. The heights of M″ obtained from the experimental plots are close to that of M″(max)=C0∕2C, co...

The results of a Mossbauer study on the effect of substitution of Al3+, Ga3+, and Cr3+ in ferromagnetic FeBO3 close to the Tc are presented. The Curie temperatures of FeBO3, Fe0.9Al0.1BO3, Fe0.9Ga0.1BO3, and Fe0.9Cr0.1BO3 have been determined to be 352, 317, 319, and 335 K, respectively. “Anomalous” spectra have been found to appear just 1° below the Tc for FeBO3, but 15° below the Tc for substituted borates. The inadequacy of static models in explaining these spectra has been pointed out. These spectra have been simulated using relaxation models and estimates of activation energy obtained for spin-flip processes. The results are attributed to dominant superparamagnetic relaxation effects due to the presence of clusters. Mossbauer spectra of FeBO3 substituted by a magnetic ion, viz., Cr3+, are found to differ significantly from those of the above-mentioned samples.

An ESR study of 1° Cu 2+ doped in zinc maleate tetrahydrate single crystal gives rise to g 1 = 2.374, g 2 = 2.257 and g 3 = 2.043. These values are quite different from the g values for the pure copper compound copper maleate tetrahydrate, viz. g | = 2.172 and g ⊥ = 2.095, indicating that in Cu 2+ /ZnMTH, Cu 2+ occupies a compressed octahedral, substitutional site with the ground state 0.724 | 3 z 2 − r 2 > + 0.173 | x 2 − y 2 >, coordinated to two maleate groups and four water molecules unlike the copper compound where coordination takes place only with water molecules. The photoacoustic spectrum of copper maleate tetrahydrate gives rise to a charge transfer band at ∼ 37 000 cm −1 and d−d transitions at ∼ 15 000 cm −1 with a shoulder at ∼ 12 000 cm −1 .

The electron spin resonance spectra of single crystals of manganese(II)-doped zinc maleate tetrahydrate have been investigated at room temperature. The transitions arise from a single type of site with gxx= 2.010, gyy= 1.992, and gzz= 2.035. The g shifts from the free spin value have been attributed to an electron-transfer process from the ligands to the S state ion. The observed angular variation of the allowed hyperfine transitions is in good agreement with theory. The spin-Hamiltonian parameters D= 360.5 × 10–4, E= 66.8 × 10–4, a=–8.9 × 10–4, and A=–87.0 × 10–4 cm–1 have been deduced. From the A value an ionicity of 96.5% is derived for the metal–ligand bonding. The analysis of forbidden hyperfine transitions leads to Q′= 1.58 × 10–4 and Q″= 0.28 × 10–4 cm–1 for the axial and rhombic components of the quadrupole coupling tensor respectively for the 55Mn nucleus.

The electron spin resonance spectra of single crystals of manganese(II)-doped zinc maleate tetrahydrate have been investigated at room temperature. The transitions arise from a single type of site with gxx= 2.010, gyy= 1.992, and gzz= 2.035. The g shifts from the free spin value have been attributed to an electron-transfer process from the ligands to the S state ion. The observed angular variation of the allowed hyperfine transitions is in good agreement with theory. The spin-Hamiltonian parameters D= 360.5 × 10–4, E= 66.8 × 10–4, a=–8.9 × 10–4, and A=–87.0 × 10–4 cm–1 have been deduced. From the A value an ionicity of 96.5% is derived for the metal–ligand bonding. The analysis of forbidden hyperfine transitions leads to Q′= 1.58 × 10–4 and Q″= 0.28 × 10–4 cm–1 for the axial and rhombic components of the quadrupole coupling tensor respectively for the 55Mn nucleus.