S. Narayana Murty

Effect of rare-earth ions on the properties of modified (SrBa)Nb2O6 ceramics

Influence du dopage sur la constante de Curie, la constante dielectrique et la temperature de Curie

Ferroelectric properties of tungsten bronze ceramics

Abstract Modified strontium barium niobate and lead potassium niobate ceramics with tungsten bronze structure were prepared by the conventional ceramic techniques. The effect of various dopants on the properties of strontium barium niobate ceramics have been investigated. Curie temperature decreases with the increase of the ionic radius of dopant. The properties of filled and unfilled structures are compared. The effect of La3+ on Lead Potassium Niobate is discussed.

Ferroelectric behaviour of lanthanum doped (NaK)NbO3 ceramics

Abstract Specimens of NaxKx−3yLayNbO3 where x = 0.5 and y = 0.05, 0.1 and 0.15 have been prepared by conventional ceramic technique. The dielectric properties and conductivity were studied as a function of temperature. Substitution of rare-earth ions in (NaK)NbO3 play an important role on the ferroelectric curie temperature as well as dielectric constant. Curie temperature decreases as the concentration of the rare-earth ions increases. Lattice parameters are determined from X-ray studies.

Modified (NaK)NbO3 ceramics for transducer applications

Abstract Solid solutions of Na x K x−3y Pr y NbO3 where x = 0.5 and y = 0.05 and 0.1 were prepared by conventional ceramic technique. Two phase transitions were observed in dielectric studies. Curie temperature decreases as the concentration of rare-earth ion increases. The monoclinic lattice parameters are calculated from X-ray studies. Mechanical quality factor and frequency constant increases with Pr3+ addition.

Effect of Nb5+ substitution on the piezoelectric properties of PLZT ceramics

Abstract The effect of Nb5+ substitution on the dielectric and piezoelectric properties of PLZT (5/65/35) ceramics are investigated for different Nb concentrations. Optimum piezoelectric properties are obtained for 0.5 mole% Nb substitution. The room temperature dielectric constant increases with Nb concentration whereas Curie temperature Tc and peak dielectric constant ϵTc decreases with increase of Nb concentration. As the Nb concentration increases from 0.5 mole% to 1.5 mole% both Kp and Kt decrease.

Relaxor behaviour in certain tungsten bronze ceramics

Abstract Relaxor ferroelectrics with high Curie temperature are attractive candidates for electro-optic and pyroelectric devices. Solid solutions of (Srx Ba1–x)0.8 Na0.4 Nb2O6 where × = 0.3 to 0.6 have been prepared by the conventional ceramic technique. The properties of relaxor ferroelectrics are dependent on ceramic processing conditions. Relaxor characteristics have been studied. A broad transition is observed in all the compositions. The broadness decreases gradually with the increase of strontium concentration.

Effect of different cations on the ferroelectric properties of modified strontium barium niobate ceramics

Strontium barium niobate (SBN) is a ferroelectric solid solution with tetragonal tungsten bronze structure [1, 2]. The structure consists of a framework of oxygen octahedra sharing corners in such a way that there are three different types of interstitial sites A, B and C. The common formula is (A1)2(A2)4(C)4(B1)2(B2)8030, where positions At , A2, BI, B2 and C can be filled by different-valency cations or may be partially empty. In tungsten bronze niobates BI and B 2 are filled by Nb 5+ . As, A2 and C could be filled by alkali and alkaline-earth metal ions from which crystals and solid solutions could be prepared with a variety of cations introduced into the structure. In many of these materials diffuse phase transition has been reported. In the work of Jimenez et al. [3] on SBN ceramics a large decrease in the Curie temperature of nearly 50 °C was reported when doped with Fe, Mn, Cr and La. Hence, in this work by doping with suitable cations we have tried to enhance Tc and decrease the dielectric loss. When the interstitial vacancies are filled partially or fully with alkali elements, Tc is raised. Hence, for filling the structure Na + was introduced. With the introduction of Na +, Aposition vacancies result from the volatility of Na. It is well known that A-position vacancies aid the sintering process. Lattice vacancies may be expected to be effective promoters of sintering because sintering is basically diffusion-controlled. Also, the ionic radius of Na + is smaller than that of Sr or Ba. This difference in ionic size is enough of a defect to cause marked lattice reconstruction by diffusion. The effect of different cations Cr 6+ , Zn 2+ and y3+ on the lattice parameters and ferroelectric properties of SrBaNb20 6 ceramics are reported in this letter. Polycrystalline solid solutions of the following compositions are prepared by the conventional ceramic processing: (Sr0.6Ba0.4)0.s RyNa0.4Nb206

Superconductivity in Pb2+ doped Dy-Ba-CuO system

Superconducting Dy0.35Ba0.65Pb0.1Cu0.9O3-δ compounds have been prepared and identified as single phase. The crystal structure was determined to be an orthorhombic derivative of the perovskite. Electrical resistivity is measured as a function of temperature. Superconducting transition was observed at 80 K.

Microstructural studies of modified SBN ceramics

Strontium barium niobate (SBN) is a ferroelectric solid solution with tetragonal tungsten bronze structure. SBN exhibits excellent pyroelectric and electro-optic properties. Solid solutions of (Sr/sub x/Ba/sub 1-x/)/sub 0.8/ Na/sub 0.4/R/sub y/Nb/sub 2/O/sub 6/ where R/sub y/=Y, Zn, Mg, Fe, have been prepared by the conventional ceramic technique. The microstructures were studied with the aid of a scanning electron microscope on fractured surfaces of ceramic compositions and the average grain diameter was measured by the linear intercept method. The results are discussed in relation to the grain sizes.

Piezoelectric (NaK)NbO3 ceramics for ultrasonic delay line applications

Abstract Solid solutions of Nax Kx-3y Ry NbO3 where x = 0.5, y = 0.05 and R = Sm, Ce have been prepared by powder-metallurgical technique. Lattice parameters were determined from X-ray studies. The effect of rare-earths on the piezoelectric and ferroelectric properties of (NaK)NbO3 ceramics have been investigated. Electromechanical coupling coefficients are measured using resonance and antiresonance technique. The quality mechanical factor(Qm) and frequency constant (Np) are found to be higher for Ce3+ composition.