D. Madhava Prasad

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.

IMPEDANCE SPECTROSCOPY STUDY OF THE FERROELECTRIC Pb0.8K0.1Dy0.1Nb2O6 CERAMICS

Polycrystalline Dy-modified Pb1-xK2xNb2O6 (PKN) ferroelectric ceramic with a general formula Pb1-xK2x-3yMyNb2O6 for x=0.20, y=0.10 and M=Dy, have been prepared by the solid-state reaction route. The X-ray diffraction (XRD) studies of the material at room temperature revealed orthorhombic structure with lattice parameters a=17.701 A, b=17.958 A and c=3.883 A. The dielectric anomaly with a sharp peak is observed at 430°C. The impedance plots are used as a tool to analyze the sample behavior as a function of frequency. The grain and grain boundary contributions are estimated. The modulus mechanism indicates the non-Debye type relaxation. The activation energy value near the phase transition temperature has been found to be different in the above TC from AC conductivity measurements.

EFFECT OF YTTRIUM ON DIELECTRIC, PYROELECTRIC AND PIEZOELECTRIC PROPERTIES OF PBN FERROELECTRICS

Materials with batch formula Pb(1-x-3y/2)RyBaxNb2O6, where R=Y, (1-x)=0.73, 0.63, 0.53 and y=0.00, 0.02 have been prepared by the double sintering method. Substitution of yttrium (Y) restored tetragonal symmetry of PBN but reduced lattice parameters, cell volume and enhanced the density. Transition temperature of PBN has decreased due to the substitution of Y3+. Enhanced room temperature spontaneous polarization (Ps)=149.97 μC/sq. cm has been observed in PBN53, which is above MPB, whereas enhanced value of Ps=112.74 μC/sq. cm is found in Y: PBN63 at MPB region. The room temperature Pyroelectric coefficient (PRT=1.07) has been observed in the composition where maximum volume of Ps is obtained. Similarly, enhanced values of piezoelectric coefficients Kp=0.244, Kt=0.353, K31=0.131, d31=60, d33=159 and g31=3.65 have also been found in the same material PBN53. Substitution of Yttrium enhanced the stiffness constant 13.59 in PBN 73 to 14.27 of Y: PBN73.

FERROELECTRIC AND PIEZOELECTRIC PROPERTIES OF Gd3+ AND Y3+ MODIFIED PKN ELECTROCERAMICS

Ceramics with the composition Pb1-xK2x-3yMyNb2O6 (PKMN) with x = 0.29, y = 0.145 and M = Gd3+, Y3+ were synthesized by the solid-state reaction route between the corresponding oxides and carbonates. The crystal structure was confirmed by X-ray diffraction (XRD). The temperature dependence of dielectric properties were measured from 35 to 595°C. Well-developed P–E (polarization–electric field) hysteresis loops were observed in the materials. Determining the piezoelectric constants, Kp = 20%, Kt = 49%, d33 = 110, and quality factor, Qm = 33, reveals that the material Y3+-modified PKN can be useful for transducer applications.