M. L. Nanda Goswami

Room temperature ferroelectric and ferromagnetic properties of multiferroics xLa0.7Sr0.3MnO3-(1 -x)ErMnO3 (weight percent x=0.1, 0.2) composites

A different kind of multiferroics with composite character, xLa0.7Sr0.3MnO3 (LSMO)–(1−x)ErMnO3 (EMO) (x=0.1, 0.2), where EMO is the ferroelectric (FE) and LSMO is the ferromagnetic (FM) component, has been studied. Magnetization versus magnetic field measurements at 300K show prominent hysteresis loops, attesting room temperature FM behavior of these multiferroic composites. Dielectric constant (e) as a function of temperature reveals that paraelectric-FE transition temperature TC* (525K) and maximum value of e (318) remain almost unaffected for x=0.1 composite compared to pure EMO. Polarization versus electric field study at 300K give conclusive evidence of the presence of spontaneous polarization in this x=0.1 composite. For x=0.2 composite, decreasing TC* (430K) with increase in e value (774) indicates diffusive FE character.

Structural and electrical properties of modified lead germanate ferroelectrics

Abstract Polycrystalline samples of modified lead germanate, Pb 4.95 A 0.05 Ge 2.5 Ti 0.5 O 11 ( A = Ca , Sr , Ba ), were prepared using solid-state reaction techniques. X-ray powder diffraction studies of the compounds suggest the formation of single phase materials of trigonal crystal structure at room temperature. Detailed studies of the dielectric constant (e) and loss (tan δ) of the compounds, both as a function of frequency (2 x 10 2 − 10 6 Hz) at room temperature and temperature (from room temperature to 200 °C) at 10, 100 and 1000 kHz, exhibit a ferroelectric diffuse phase transition. The transition temperature is found to decrease with Ba, Sr and Ca doping at the Pb site. The biasing field and temperature dependence of dc electrical conductivity were measured for all the compounds. The nature of the ferroelectric phase transition was checked by measuring the temperature dependence of the polarization.

Successive phase transition in T1NaWO4 ceramics

Abstract Polycrystalline samples of T1NaWO4 ceramics have been prepared by conventional solid-state reaction technique at low temperature (600 °C). Preliminary, room temperature X-ray studies suggest the formation of single phase desired compound with cell parameters a = 10.3257 A , b = 11.1268 A and c = 16.1951 A in the orthorhombic crystal structure. Detailed studies of dielectric constant (ϵ) and loss (tan δ) as a function of frequency and temperature suggest that the compound undergoes two successive phase transitions at 10 °C and 60 °C.

Diffuse phase transition in modified lead germanate ferroelectrics

Polycrystalline samples of modified lead germanate, Pb4.9A0.1Ge2TiO11 (A = Ca, Sr, Ba) were synthesized by a solid-state reaction technique. Studies of x-ray powder diffraction patterns and scanning electron microscopy images of these compounds at room temperature suggest that the compounds have been formed almost in a single phase with a trigonal crystal system and a uniform grain distribution throughout the surface of the samples. Detailed studies of dielectric properties of the compounds as a function of frequency (2×102 to 106 Hz) at room temperature, and for temperatures from room temperature to 200 °C at 10, 100 and 1000 kHz show broadening (diffuseness) of the dielectric peaks and a change of the transition temperature with the ionic size of the dopants. The temperature dependence of the electrical conductivity, polarization and pyroelectricity for all these compounds provide some interesting results for device fabrication.

Ferroelectric phase transition in TlKWO4

Abstract The polycrystalline samples of TlKWO4 have been synthesized by solid-state reaction technique. Preliminary X-ray powder diffraction studies of the compound suggest the formation of single phase material in the orthorhombic crystal system. Measurements of dielectric constant (e) and dielectric loss (tanλ) as a function of temperature have shown dielectric anomaly and spontaneous polarization disappears at 44±1° which clearly suggest the ferroelectric phase transition in this compound.

Phase transition in Pb5Ge2ZrO11 ceramics

Abstract Polycrystalline samples of zirconium-doped lead germanate Pb 5 Ge 2 ZrO 11 were prepared by a solid-state reaction technique. Preliminary X-ray studies show the formation of the single-phase compound and provided its basic crystal structure. Dielectric constant (ϵ) and loss (tan δ) were measured as a function of temperature (room temperature to 280°C) at different frequencies. Dielectric anomaly and ferroelectric phase transition observed at 160°C was supported by our polarization studies. The activation energy of the sample was calculated from the dielectric data.

Diffuse phase transition in modified Pb5Ge3O11 ceramics

Abstract Polycrystalline samples of Pb4,9A0.1Ge2.5Ti0.5O11 (A = Ca, Sr, Ba) have been prepared by solid-state reaction technique. Studies of X-ray powder diffraction patterns of these compounds at room temperature suggest that the compounds have been formed almost in single phase with trigonal crystal system. Detailed studies of dielectric properties of the compounds as a function of frequency (0.2 kHz to 1 MHz) at room temperature (RT), and for temperatures RT to 200°C at 10, 100 and 1000 kHz show broadening (diffuseness) of the dielectric peaks and change of transition temperature with the ionic size of the dopants. Analysis of diffuseness of the dielectric peaks shows that the values of 7 (diffusivity) lie between 1 and 2, which indicate the variation of the degree of disordering of the system caused due to substitution of different ions. Temperature dependence of electrical conductivity and polarization of these compounds provide some interesting results for device fabrication.

Ferroelectric phase transitions in modified lead germanate

Abstract Polycrystalline samples of modified lead germanate, Pb4.95A0.05Ge2TiO11 (A = Ca, Sr, Ba), were prepared by solid-state reaction techniques. Preliminary structural studies showed that the basic structure of Pb5Ge3O11 remains unchanged on the substitution of Ca2+, Sr2+, Ba2+ ions at the Pb2+ site (in small amounts) and Ti4+ at the Ge4+ site. Dielectric constant (e) and loss tangent (tan Δ) were measured as functions of frequency (2 x 102 to 106Hz) and temperature (30°C to 200°C). It was found that the transition temperature shifts towards room temperature due to the above substitutions. From the dielectric measurements, ac conductivity and activation energy of the compounds were calculated. Measurement of polarization as a function of temperature confirmed the shift in the transition temperature. The nature of the phase transition in the modified lead germanate compounds is found to be second order.

Structural and electrical properties of TlLiWO4 ceramics

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