• R N P Choudhary

Articles written in Pramana – Journal of Physics

• A neutron diffraction study of ferroelectric PbHAsO4 at room temperature

A single-crystal neutron-diffraction structural study of PbHAsO4 in its ferroelectric phase at room temperature (24°C) is presented as part of an investigation of a family of monetites. The crystal structure of PbHAsO4, and its phase transition mechanism are discussed. Comparison of the crystal structures of PbHPO4 and PbHAsO4 reveals that these two ferroelectrics are isomorphous. The role of protons in structural phase transition of PbHAsO4 is also discussed.

• X-ray and dielectric studies of Sm2(MoO4)3

The polycrystalline samples of Sm2(MoO4)3 have been prepared by heating appropriate quantities of oxides. The X-ray powder diffraction technique has been used to provide information about lattice parameter, space group and basic structure. The dielectric constant has been measured as a function of frequency (560 Hz-13 MHz) and temperature (30–220°C) to know the ferroelectric transition temperature.

• Synthesis and dielectric properties of Ba3NaRNb10O30 [R = La and Sm]

Polycrystalline samples of Ba3NaRNb10O30 (R = La and Sm) have been prepared by high temperature solid-state reaction method. The X-ray powder diffraction technique has been used to test the formation of the compounds. Lattice parameters, space groups and basic structures of the compounds have been obtained from X-ray data. The dielectric constant has been measured as a function of frequency (100 Hz–10 kHz) and temperature (−180 to 200°C) to understand transition mechanism in these ferroelectric compounds.

• Structural and dielectric properties of Pb5(Ge,Si)O11

The ferroelectric lead germanate (Pb5Ge3O11) and its isomorphous compounds are important because of their uses as pyroelectric and electro-optic devices. Comparison of inter-planar d-spacings of Pb5Ge3−xSixO11 (x=0, 0.3, 0.7 and 1.00) suggests that there is no change in basic structure of Pb5Ge3−xSixO11 when Si is substituted for Ge in small quantity (x&lt;1). The dielectric properties of the Si-substituted compounds have been studied as a function of temperature (30 to 200°C). The ferroelectric-paraelectric phase transition has been observed at 185°C. The Si doping causes (a) Curie point to shift towards low temperature, (b) peak value of the dielectric constant to decrease and (c) phase transition diffuse. The fast increase in dielectric constant of pure Pb5Ge3O11 with temperature (beyond transition temperature) may be attributed to the development of space charge polarization in the system.

• Dielectric properties of Pb(Mg1/4Zn1/4Nb1/2)O11/4

Polycrystalline samples of Pb(Mg1/4Zn1/4Nb1/2)O11/4 have been synthesized by high temperature columbite precursor solid state reaction technique. Using X-ray diffraction (XRD) technique, compound formation in single phase cubic structure was observed and XRD analysis provided preliminary structural data. Detailed studies of dielectric properties of the compound reveal that this compound has high dielectric constant and diffuse phase transition in a wide range of temperatures around the Curie temperature. The charge deficiency of the compound presumably gets compensated in the high temperature columbite precursor process of sample preparation which is supported by single phasic form of the material.

• Structural, spectroscopic and dielectric properties of KVO3

Polycrystalline samples of KVO3, a member of the pyroxene structural family have been synthesised with high-temperature solid-state reaction technique. Preliminary structural and spectroscopic and detailed dielectric properties have been studied in different conditions. No dielectric anomaly or hysteresis loop has been observed in a wide temperature range (30°C to 450°C). Basic structural and spectroscopic (IR and Raman) studies suggest that at room temperature, KVO3 is centrosymmetric as reported earlier. This and other observations do not support the recent report of ferroelectric phase transition in the compound.

• Structural and dielectric properties of Pb(Li1/4Dy1/4W1/2)O3

The polycrystalline samples of Pb(Li1/4Dy1/4W1/2)O3 have been synthesized by high-temperature solid-state reaction techniques. Room temperature X-ray diffraction (XRD) studies of the compound provided preliminary structural data, and hence formation of a single phase desired material was confirmed. Detailed studies of dielectric constant (ε) and loss (tanδ) as a function of frequency (100 Hz to 10 kHz) at room temperature (298 K) and also as a function of temperature (liquid nitrogen to 403 K) at 10 kHz suggest that the compound undergoes a ferroelectric phase transition of diffuse type.

• Excitation performance of $\rm{Ba_{0.8}Mg_{0.2}(Zr_{0.1}Ti_{0.8}Ce_{0.1})O_{3}}$ materials in an electrical field

Dense and stoichiometric $\rm{Ba_{0.8}Mg_{0.2}(Zr_{0.1}Ti_{0.8}Ce_{0.1})O_{3} (BMZTCO)}$ ceramics have been synthesised and their excitation was experimentally evaluated by applying an electric field. The processed sample exhibits superior frequency-independent and temperature-dependent dielectric parameters. The prepared sample has combined the tetragonal and cubic phases of $\rm{BaTiO_{3}}$ and $\rm{Ce_{2}O_{3}}$. The Bode plots suggest non-Debye type of relaxation mechanism and positive temperature coefficient-type behaviour. The excitation intensity reaches a peak when the driving frequency matches with the natural frequency of the prepared sample.

• # Pramana – Journal of Physics

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Volume 93 | Issue 5
November 2019

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