• Volume 15, Issue 3

      June 1992,   pages  189-287

    • Foreword

      P Rama Rao K J Raj

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    • Proton transport in KDP-family of ferroelectric materials

      Ajay Kumar S A Hashmi Suresh Chandra

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      Proton transport in potassium dihydrogen phosphate (KDP) and ammonium dihydrogen phosphate (ADP) is briefly reviewed. The experimental results of Wagner’s polarization measurement, coulometry, infrared spectroscopy, transient ionic current measurement, the variation of electrical conductivity with temperature and electrogravimetric analysis for KDP and ADP are reported. H+ and OH- ions are ascertained as the mobile ionic species. A new mechanism for the proton transport in KDP and ADP is suggested: A three-fold rotation of H2P4- units about any of the axes of PO4 tetrahedra leads to a configuration like O...H...H...O, the rearrangement of which provides H...O...H bridge that gets electrodissociated on the application of a d.c. electric field.

    • Dielectric function for the Anderson model

      A Ramakanth

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      In recent years the study of alloys and compounds containing rare-earth and actinide elements is receiving increasing attention. The Anderson model is most popularly used for studying the theory of these systems. As it displays a large number of anomalous characters in magnetic and electrical properties, it was felt worthwhile to study the dielectric properties of this model. Using the linear response theory of Kubo, the energy and wave vector-dependent dielectric function$$\varepsilon \left( {\bar q,E} \right)$$ is related to the retarded Green’s function of Fourier components of electron density fluctuations$$\left\langle {\left\langle {\rho _{\bar q} ;\rho _{ - \bar q} } \right\rangle } \right\rangle $$. Thus a many-body calculation of$$\varepsilon \left( {\bar q,E} \right)$$ requires the calculation of$$\left\langle {\left\langle {\rho _{\bar q} ;\rho _{ - \bar q} } \right\rangle } \right\rangle $$. The Greens function is calculated using the equation-of-motion method with RPA decoupling. Further, since certain ensemble averages are required as inputs to the calculation, the relevant single-particle Green’s functions are also evaluated.

    • Characteristics of materials for microwave devices

      V R K Murthy K C James Raju B Viswanathan

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      The characteristics of materials like ferrites, garnets, ferroelectrics temperaturecompensated dielectrics and copper-coated PTFE-based composites, extensively used in microwave devices are discussed.

    • Defect characterization of KTP single crystals

      G Dhanaraj T Shripathi H L Bhat

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      Potassium titanyl phosphate (KTP) is a relatively new nonlinear optical material with excellent combination of physical properties. This paper presents the combined etching and X-ray topographic studies carried out on KTP crystals with a view to characterizing their defects. KTP crystals employed in this investigation were grown from flux. Optical microscopic study of habit faces revealed growth layers and growth hillocks on (100) and (011) faces respectively. Etching of (011) habit faces proved that growth hillocks corresponded to the emergence point of dislocation out crops on these faces. The suitability of the new etchant to reveal dislocation was confirmed by etching the matched pairs obtained by cleaving. The defects present in the crystal were also studied by X-ray topography. The defect configuration in these crystals is characteristic of crystals grown from solution. The dislocations arc predominantly linear with their origin either at the nucleation centre or inclusions. In general, grown crystals were found to have low dislocation density and often large volumes of crystals free from dislocation could be obtained.

    • Proton conduction in solids—A Raman spectral study

      G Aruldhas

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      The mechanism of proton conduction in hydrogen-bonded solids and the importance of Raman investigations to understand it are discussed here. The results of Raman investigations on the protonic conductors (NH4)3H(SO4)2 and Li2SO4·H2O under small d.c. electric fields have been discussed. The enhancement in intensity of the 859, 829 and 330 cm−1 bands of(NH4)3H(SO4)2 has been explained on the basis of proton movement along the N-H...O bond. Spectral changes of the bands due to torsional oscillation of the ammonium ion indicate the probability of hindered rotation of this group. The appearance of new bands at 773 and 1680cm−1 in Li2SO4·H2O indicates the formation of H3O+ electrolysis. The changes in stretching and bending modes of water are explained on the basis of polarizability changes induced by the migration of proton along the 0-H...0 bond and reorientation motion of water molecules.

    • Dielectric properties of perovskite crystals

      B S Semwal N S Panwar

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      The soft mode dynamical model has been used to study the dielectric properties of Perovskite-type crystals. The model Hamiltonian proposed by Pytte has been modified and designed in terms of creation and annihilation operators. The correlations appearing in the dynamical equation have been evaluated using double time thermal retarded Green’s function and Dyson’s equation. Without any decoupling the higher order correlations have been evaluated using the renormalized Hamiltonian and thus, all possible interactions among phonons have been taken into account. The expressions for phonon frequencies and widths have beenMcalculated. Using appropriate parameters the softening of different modes at different transition temperatures give rise to a series of transitions from cubic to tetragonal, orthorhombic or trigonal phases. The significantly temperature-dependent modes are considered responsible for damping constant, dielectric constant, tangent loss and attenuation constant for these crystals. The dielectric properties are directly related to the optical phonon frequencies and widths and acoustic attenuation to the acoustic and optical phonon widths. Using suitable approximations, the model explains the experimental results on dielectric properties and acoustic attenuation reported for LiNbO3, SrTiO3, BaTiO3 and LaAlO3.

    • Cooperative ordering of impurity dipoles in KNbO3 single crystals

      S G Ingle K S Moon R N Kakde

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      The impurity atoms forming dipoles in the structure of KNbO3 are arranged regularly in the structure. The locations of the dipole sites were observed by etching technique, when dilute HNO3 was used as an etchant. The dipoles along with the domain structure with which they are associated are stable with respect to temperature, and retain the same sites at Curie temperature. Thus the regular cooperative ordering observed at room temperature also exists at the Curie transition. The importance of this ordering is discussed in terms of domain formation and the basic problem of ferroelectricity in crystals.

    • Influence of internal phase properties on zeta-potential and dielectric constant of o/w emulsion

      Devraj Rambhau A K Dorle B Rami Reddy

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      Dielectric constant (DEC) of internal phase influenced the zeta potential (ZP) of o/w emulsion prepared with or without emulgent. In both systems ZP and DEC of internal phase exhibited an approximately linear relationship. Using homologous aliphatic hydrocarbons as internal phases, emulsions were prepared with polysorbate-80. Increase in carbon chain length brought about increase in interracial area and decrease in ZPs of emulsions. A fair inverse correlation between ZP and DEC of internal phase was revealed in this series. Increase in phase volume ratio from 0.05 to 0.3 brought about limited changes in ZPs whereas by further increasing phase volume ratio, ZP decreased steadily. Studies pertaining to the effect of phase volume ratio on DEC of o/w emulsions are in accordance with earlier observations. Increase in phase volume ratio causes a steady decrease in DEC of emulsion. Of the five equations employed, the Bruggeman equation appears to predict the observed values more accurately.

    • Relaxor ceramics for multilayer capacitor application

      P Roy-Chowdhury

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      Relaxor ferroelectrics, lead magnesium niobate (PMN) and lead zinc niobate (PZN) and their solid solution with lead titanate (PT) and barium titanate (BT) were studied. Unlike lead magnesium niobate, the pyrochlore-free material for lead zinc niobate could not be prepared by reaction between lead niobate and ZnO below 1000°C. However, some improved composition was obtained when lead zinc niobate (85%) and a mixture of lead titanate (10%) and barium titanate (5%) sintered at 950°C. XRD examination of the samples revealed that lead magnesium niobate prepared by us contained 9.9% pyrochlore phase, whereas the solid solution between 90% lead magnesium niobate and 10% lead titanate was completely free from the same phase. The dielectric constant for PZN-PT-BT (85:10:5) ternary system was 4000, whereas the same for lead magnesium niobate and its solid solution with 10% lead titanate was 4100 and 6000 respectively. The comparatively low value obtained for PZN-PT-BT solid solution was probably due to the presence of appreciable amount of pyrochlore phase. The grain diameter for PMN and PMN-PT (90:10) solid solution was 1.37/μM and 2.34μM respectively.

    • Characterization and dielectric properties of almandine-pyrope garnet

      K Krishna Kumar V Balaram Lalitha Sirdeshmukh

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      Some garnets collected from the Kothagudem area of Khammam district in Andhra Pradesh were characterized by chemical analysis. The results show the garnets to be of almandine (Fe+23 Al2Si3O12) pyrope (Mg3Al2Si3O12) group. Dielectric constant (ɛ) and dielectric loss (tanδ) were measured as a function of frequency and temperature in the frequency range of 100 Hz to 100 KHz and from room temperature to 400°C. The room temperature measurement was extended to 10 MHz, AC conductivity was calculated from the data on ε and tan δ. DC conductivity was also measured.

    • Phase boundaries and domain boundaries in crystals

      H Klapper TH Hahn H-D Jennisen

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      Domain boundaries, i.e. interfaces between different orientation variants of the same crystal species, and phase boundaries, i.e. interfaces between two different modifications of the same compound, exhibit rather similar features. This has been investigated by means of polarized light and X-ray topography for a series of structurally related sulphates which were grown as large single crystals from aqueous solution. The major results are as follows:

      (i) Domain interfaces frequently adopted only a few orientations which are low-energy boundaries of best structural fit. These preferred orientations may be parallel to low-indexed lattice planes or to non-crystallographic planes (W and Wt walls according to the classification of Sapriel,Phys. Rev. B12, 1975, 5128). Illustrations of such (transition-induced) domain boundaries in KLiSO4, NH4LiSO4, RbLiSO4, CsLiSO4,(NH4)3H(SO4)2 will be presented.

      (ii) For many first-order transitions the phase boundaries prefer planes of minimum strains, i.e. low energy, which again may be low-index lattice planes or non-crystallographic planes. These preferred orientations can be calculated from the strain tensor of the transition with the relative lattice-parameter changes as tensor components). If the transition isotherm deviates from the minimum strain orientation, characteristic zigzag boundaries with segments parallel to the (symmetrically equivalent) preferred planes may result. Zigzag phase boundaries have been observed in RbLiSO4 and {N(CH34}2ZnCl4.

      (iii) The shape and the density of transition-induced domains is influenced by the orientation of the phase boundaries and its velocity of motion. For the 708 K. transition of KLiSO4 and the 413 K transition of (NH43H(SO42 (in both cases loss of the trigonal axis), among the minimum-strain domain boundaries those normal to the phase boundary are preferred. In N(CH3)42ZnCl4, the domain density increases with the phase boundary velocity.

    • Ferroelectric films for non volatile-memory applications

      K Sreenivas

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      Microelectronic applications of ferroelectric thin films have undergone a resurgence. Recent advances in deposition technologies and the achievement of bulk properties in thin films have enabled successful integration and fabrication of ferroelectric random access memories onto standard integrated circuits that combine high speed, complete non-volatility and extreme radiation hardness. Current research covers both the basic and applied areas in ferroelectric material science and semiconductor device development.

      In this talk the evolution of solid state memory devices in conjunction with silicon technology will be described, and the increasingly important role expected from ferroelectric materials highlighted. In coupling ferroelectric thin film processing with Si technology several new problems have to be resolved. The device physics and design, the material choice for ferroelectric memories, thin film preparation and characterization, and the problems of fatigue and retention will be discussed.

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