K. Sambasiva Rao

Dielectric and pyroelectric properties of BSNN ceramics: effect of Ba/Sr ratio and La2O3 addition

The (Ba1−xSrx)2NaNb5O15, [BSNN] system is a lead free ferroelectric material that has large spontaneous polarization, pyroelectric coefficient, a low dielectric constant and is expected to be applicable for piezoceramic filter and pyroelectric detector devices. Pyroelectric detector materials require low dielectric constant and high pyroelectric coefficient with a high figure of merit. Effect of lanthanum (La) on pyroelectric coefficient, dielectric constant, spontaneous polarization and resistivity at and around morphotropic phase boundary (MPB) region of BSNN ceramics is presented in this article.

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

Anomalous electrical behaviour of barium sodium niobate ceramics doped with trivalent lanthanum

Orthorhombic tungston bronze type ferroelectric barium sodium niobate (BNN) has been found to be an outstanding non-linear optical material and is particularly useful for the second harmonic generation. Van Uitert et al. [1] has studied d.c. resistivity in BNN single crystal and estimated activation energies in the temperature ranges 480 to 700 K and 770 to 900 K which cover the Curie temperature of the material) to be 1.00 and 1.33 eV, respectively. Further, resistivity is decreased with increasing temperature in the range 480 to 900 K showing negative temperature coefficient effect in BNN, and a maximum resistivity of the order of 10 l° l)cm was obtained. In this letter d.c. resistivity studies on rare-earth lanthanum-doped barium sodium niobate are reported for the first time.

INFLUENCE OF SAMARIUM SUBSTITUTION ON IMPEDANCE DIELECTRIC AND ELECTROMECHANICAL PROPERTIES OF Pb(1-x)K2xNb2O6

Ferroelectric, hysteresis, impedance spectroscopy parameters, AC conductivity, and piezoelectric properties in the ceramics of Pb0.74K0.52Nb2O6 and Pb0.74K0.13Sm0.13Nb2O6 have been studied. X-ray diffraction study reveals single phase with the orthorhombic structure. The samples were characterized for ferroelectric and impedance spectroscopy properties from room temperature to 600°C. Cole–Cole plots (Z″ versus Z′) are drawn at different temperatures. The results obtained are analyzed to understand the conductivity mechanism in both the samples. The piezoelectric constant d33 has been found to be 96 × 10-12 C/N in PKN.

Ferroelectric and resistivity studies on modified Sr6Ti2Nb8O30 ceramics

Abstract Solid solution of Sr6RxTi2Nb8030 (where × = 0.0, 0.1, R = La, Pr, Nd, Sm and Gd) have been synthesized. Orthorhombic symmetry has been identified from XRD studies. Substitution of rare-earth ion in STN effects the unit cell dimension and curie temperature of STN. Resistivity studies in STN and doped STN indicated an anomalous behaviour. This behaviour has been interpreted on the basis of Heywangs model.

Influence of Rare-Earth Ion on Piezoelectric and Pyroelectric Properties of PBN System

Lead Barium Niobate, Pb1− x Ba x Nb2O6 (PBN) is a ferroelectric with tungsten bronze type structure. At room temperature PBN crystal for x = 0.37, possesses a density of 5.93 g/cm3, spontaneous polarization, P s , 3.8 × 10− 5 C/cm2, Coercive field (E c ), 1.1 kV/mm and pyroelectric coefficient (P RT ), 9 × 10− 5 C/cm2°C has been reported. Present communication describes preparative conditions, structure and microstructure, hysteresis loop, permittivity, pyroelectric, piezoelectric and resistivity properties of unmodified and dysprosium modified PBN compositions. The values of P s , 149.97 μ C/cm2, P RT , 1.07 × 10− 7 C/cm2°C in PBN:3 for x = 0.47 have been observed. The value of P RT , 1.15 × 10− 7 C/cm2C in Dy:PBN: 1 has been noticed. The observed piezoelectric constants in PBN:3 are k p = 0.244, k t = 0.353, d31 = −60 × 10−12 C/N, d33 = 159 × 10− 12 C/N, s11 E = 12.52 × 10− 12 m2/N.

Influence of Pr 2 O 3 and Nd 2 O 3 on Ferroelectric and Pyroelectric Properties of Tungsten Bronze Structured BSNN Ceramics

Present communication describes the preparation and the influence of Pr 2 O 3 and Nd 2 O 3 on structure, ferroelectric, dielectric, pyroelectric and resistivity properties of (Ba 1-x Sr x ) 2 NaNb 5 O 15 [BSNN] compositions at and around x = 0.6, MPB region. Substitution of Pr 2 O 3 /Nd 2 O 3 decrease the cell volume and Curie temperature and enhance the room temperature dielectric constant. The room temperature pyroelectric coefficients are observed to be in the order of 10-9 C/cm 2 °C. Higher figure of merit FM RV , FM RN and FM RI values of the order 10-14 CM/J, 10-12 CM/J and 10-11 CM/J respectively are observed in both Pr/Nd:BSNN compositions. Resistivity studies revealed a PTCR behavior.

Microstructural and anomalous resistivity behavior of modified ferroelectric Ba6Ti2Nb8O30

Abstract The present communication describes the preparation and characterisation of Ba6-3x R2 xTi2Nb8O30 (where x = 0.0 and 0.05, R = La, Pr, Nd, Sm and Gd) Ceramics. Tetragonal symmetry has been noticed from XRD studies. Microstructural studies using SEM revealed, substitution of rare-earth ion in BTN inhibits the grain growth of BTN. DC resistivity measurements in these compositions indicated PTCR anomalous behaviour. This type of behaviour is explained on the basis of Heywangs model. Curie temperature of rare-earth substituted BTN found to decrease from the value of BTN.

Structural and electrical properties of dy-doped barium sodium niobate ceramics

Abstract It is proposed to discuss the experimental results concerning the influence of the Dy3+ amount of Barium Sodium Niobate (BNN) ceramics on their structural and electrical properties in this paper. X-ray diffraction, SEM, electrical (dielectric and resistivity), and piezoelectric measurements were carried out for ceramics of composition Ba4-2xNa2 + xDyx 3+Nb10O30 with x = 0.3, 0.5 and 0.7 processed by the usual ceramic method. X-ray diffraction studies showed a single phase in all the compositions with a tetragonal tungsten bronze (TB) symmetry. SEM micrographs reveal an inhibition of grain growth with Dy and is in the range 1 ∼ 3 μm. The room temperature dielectric constant, broadening of the dielectric constant versus temperature curves are observed to increase and the ferroelectric curie temperature (Tc ) decreases with the Dy concentration. It is interesting to note that a PTC effect has been observed in all the compositions and the region of the section of PTC shifted to higher temperatures wi...

SYNTHESIS, PIEZOELECTRIC, DIELECTRIC AND CONDUCTIVITY STUDIES ON Dy2O3 SUBSTITUTED (Bi0.94Na0.94)0.5Ba0.06TiO3 CERAMICS

Polycrystalline (Bi0.94-xDyxNa0.94)0.5Ba0.06TiO3 ceramics (x = 0, 0.04, and 0.08, designated as BNBT6, BNBT6: 4Dy and BNBT6: 8Dy, respectively) were prepared by conventional high temperature sintering method. The X-ray diffraction patterns show pure perovskite structure with no secondary phases. Lattice parameters and unit cell volumes have decreased due to Dy2O3 substitution. SEM micrographs revealed denser samples (ρrel > 97%) with uniformly distributed grain sizes. The room temperature piezoelectric properties of Dy2O3 substituted sample at x = 0.04 were relatively higher: d33 = 147 pC/N, kp = 28% and Qm = 128. The samples exhibited infinitesimal change in thickness (≈ 15 nm) to an applied voltage of 100 V, which could be utilized in actuator applications. Relaxor behavior and broad dielectric maxima with diffuse phase transition were observed. The value of RT dielectric constant has increased while dielectric loss was decreased due to Dy2O3 substitution. Conductivity in the materials obeys Jonschers universal power law. The conductivity in the low frequency region is associated with short range translational hopping while it is associated with the reorientational hopping in the high frequency region. The charge carrier concentration term remained constant over the entire temperature range of (30–500°C).