A. Plaude

Structure and Dielectric Properties of Na1/2Bi1/2TiO3-BaTiO3 Solid Solutions

Dielectric properties, polarization and x-ray diffraction are studied for (1-x)Na_1/2Bi_1/2TiO₃-xBaTiO₃ solid solutions in a concentration range above the morphotropic phase boundary. It is showed that all the studied compositions have tetragonal structure with maximal tetragonality slightly above the morphotropic phase boundary. Ferroelectric relaxor behavior is observed in a wide concentration range of BaTiO₃. Stability of the relaxor state decreases with increasing BaTiO₃ concentration, but only for compositions with low Na_1/2Bi_1/2TiO₃ content the normal ferroelectric-paraelectric phase transition, which is characteristic to pure BaTiO₃, occurs. Mechanisms, which influence the change of the phase transition character and promote the appearance of the relaxor state, are discussed. The phase diagram of (1-x)Na_1/2Bi_1/2TiO₃-xBaTiO₃ is revised.

Structure and dielectric properties of Na0.5Bi0.5TiO3-CaTiO3 solid solutions

Despite wide studies of Na0.5Bi0.5TiO3, structure of this material and its connection with the observed physical properties still raise numerous questions due to mutually contradicting results obtained. Here, structure and dielectric properties of poled and unpoled Na0.5Bi0.5TiO3-CaTiO3 solid solutions are studied, projecting the obtained concentration dependence of structure and dielectric properties on pure Na0.5Bi0.5TiO3 as the end member of this material group. X-ray diffraction patterns for Na0.5Bi0.5TiO3-CaTiO3 solid solutions reveal dominating of an orthorhombic Pnma phase, even for the compositions approaching the end composition (Na0.5Bi0.5TiO3), whereas structure of pure Na0.5Bi0.5TiO3 can be considered, assuming coexistence of rhombohedral and orthorhombic phases. This allows one to avoid appearance of a large difference of rhombohedral distortions between the unpoled and poled Na0.5Bi0.5TiO3, if the rhombohedral distortion is calculated as for single R3c phase. Features of dielectric permittiv...

X-ray diffraction and Raman spectroscopy studies in Na1/2Bi1/2TiO3-SrTiO3-PbTiO3 solid solutions

ABSTRACT The long and short range orders in 0.4Na1/2Bi1/2TiO3-(0.6-x)SrTiO3-xPbTiO3 solid solutions were studied by x-ray diffraction and Raman spectroscopy. X-ray diffraction patterns for these compositions in the relaxor state are different for bulk and powdered samples. It was found that, in spite of different tetragonality depending on PbTiO3 content, the Raman spectra suggest similarity of local structure for all studied compositions. Both methods indicate a disappearance of tetragonal phase upon increasing temperature.

Dielectric and Polarization Properties of Na0.5Bi0.5TiO3-BaTiO3 Solid Solutions with Na and K Niobates

The role of substitution in A- and B-sites of perovskite ABO3 structure in phase transitions is evaluated, comparing (1-y)(0.939Na0.5Bi0.5TiO3-0.061BaTiO3)-yKxNa1-xNbO3 solid solutions with x = 0.0, x = 0.5 and x = 1.0. The influence of deviation from a stoichiometric Na/Bi ratio is also studied. The influence of K0.5Na0.5NbO3, NaNbO3 or KNbO3 reduces mainly to suppressing of ferroelectric properties, like in other perovskite ferroelectrics where Ti is replaced by Nb, and development of the relaxor state. Besides the frequency-dependent dielectric permittivity, the relaxor state in the studied compositions is characterized also by a temperature dependence of critical electric fields, corresponding to phase transitions between relaxor and ferroelectric states. The influence of Nb in the above mentioned compositions is compared with the one of compositions far from the morphotropic phase boundary by a study of solid solutions (1-y)(0.80Na0.5Bi0.5TiO3-0.20BaTiO3)-yKxNa1-xNbO3.

The Effects of 3d Admixtures on Properties of Relaxor PLZT8/65/35 Ceramics

A study of the effects of the 3d dopants Mn, Fe, Co, Ni, and Cu on relaxor behavior and other properties of the ferroelectric PLZT8/65/35(La8) ceramic compound by X-ray diffraction, electron microscopy and other techniques is reported. The complex dielectric permittivity ϵ* = ϵ′-iϵ′′ is measured in the 20–400°C range of temperature at frequencies within the range of 102 – 106 Hz. Essential changes caused by the admixtures in the behavior of dielectric permittivity with frequency and temperature are observed along with changes in the XRD SEM patterns are observed. The mechanisms of the phenomena are discussed.

Structure and dielectric properties of Na 1/2 Bi 1/2 TiO 3 -BaTiO 3 solid solutions

Dielectric properties, polarization and x-ray diffraction are studied for (1−x)Na 1/2 Bi 1/2 TiO 3 -xBaTiO 3 solid solutions in a concentration range above the morphotropic phase boundary. It is showed that all the studied compositions have tetragonal structure with maximal tetragonality slightly above the morphotropic phase boundary. Ferroelectric relaxor behavior is observed in a wide concentration range of BaTiO 3 . Stability of the relaxor state decreases with increasing BaTiO 3 concentration, but only for compositions with low Na 1/2 Bi 1/2 TiO 3 content the normal ferroelectric-paraelectric phase transition, which is characteristic to pure BaTiO 3 , occurs. Mechanisms, which influence the change of the phase transition character and promote the appearance of the relaxor state, are discussed. The phase diagram of (1−x)Na 1/2 Bi 1/2 TiO 3 -xBaTiO 3 is revised.

The domain structure in PLZT (6-8)/65/35 and spontaneous ferroelectric-relaxor phase transition

Abstract In order to test the hypothesis proposed in Reference 10 about a spontaneous relaxor-ferroelectric phase transition in PLZT (6-7)/65/35 the hysteresis loops and domain structure measurements were carried out. The results confirm this hypothesis. The appearance of the ferroelectric long range order in PLZT with decreasing concentration of La ions is explained by a larger coupling between the feroelectrically active BO6 octahedrons due to smaller concentration of defects and higher dielectric constant.

Domain structure of doped PLZT ceramics

Abstract Results of microstructure studies of Cr, Mn, Fe, Co, Ni and Cu doped PLZT 8/65/35 ceramics are reported. Most of them are explained by dopant-induced domain structure in PLZT ceramics.

Electron-microscopy studies of pure and doped electrooptic PLZT ceramics

Abstract Data on chemical composition and spatial fluctuations thereof as well as fracture mode behaviour of pure and doped PLZT ceramics have been obtained.

Structure and dielectric properties at phase transition of Na1/2Bi1/2TiO3-BaTiO3 solid solutions

ABSTRACT Phase coexistence region is studied by x-ray diffraction for Na1/2Bi1/2TiO3-BaTiO3 solid solutions in the tetragonal phase side from the morphotropic phase boundary. The first order ferroelectric phase transition, determined from a jump in the temperature dependence of dielectric permittivity, is located inside the coexistence region of cubic and tetragonal phases and is below the temperature, where tetragonality disappears. At low BaTiO3 concentrations phase transition into ferroelectric state at cooling is slowly approached in time and is smeared over large temperature range. Rietveld method, applied for more precise evaluation of phase content, reveals large local deformations inside the ferroelectric phase.