M. Karpierz

Influence of Compressive Stress on Dielectric and Ferroelectric Properties of the(Na0.5Bi0.5)0.7Sr0.3TiO3 Ceramics

Good quality lead-free ceramics of (Na0.5Bi0.5)0.7Sr0.3TiO3(NBTS30) have been produced by a solid phase sintering process. The dependence of dielectric and ferroelectric properties on the unaxial pressure (0–1200 bar) were investigated. A shift and decrease of maximum value of e, decrease of the thermal hysteresis and coercive field and increase of polarization with increasing pressure were observed. The results were discussed in terms of an elastic changes in inter-ionic distances in a crystal structure and switching nanoregions under the action of pressure. The NBTS30 ceramic is expected to be a new promising candidate for lead-free electronic material.

Effects of PbTiO3 doping on electric properties of Na0.5Bi0.5TiO3 ceramics

ABSTRACT Good quality ceramics of (1−x)Na0.5Bi0.5TiO3(NBT)−xPbTiO3 (PT) (x = 0, 0.03 and 0.05) were prepared by a conventional solid-phase sintering process. The temperature dependence of the dc, ac conductivity ( respectively), the Seebeck coefficient (α), the concentration of charge carriers n and their mobility μ were investigated. The dc conductivity for pure NBT possesses three linear parts with three different activation energies Ea. For 0.97NBT–0.03PT and 0.95NBT--0.05PT ceramics, the dc conductivity also has three linear parts (three different Ea). On the other hand, the ac conductivity possesses three linear parts for pure NBT and four for other compositions. The possible origin of the observed effects is discussed. We suggest that the presented materials can be a good starting point for the development of low-lead electronic ceramics.

Thermal, Raman and dielectric study of 0.5K0.5Bi0.5TiO3–0.5PbTiO3 ceramics

The 0.5K0.5Bi0.5TiO3–0.5PbTiO3 ceramics were prepared by following a standard solid-state method. The Raman, thermal and dielectric properties of these ceramics were investigated. The X-ray measurements showed that samples have single perovskite-type structure with tetragonal symmetry. Dielectric study revealed that the dielectric behaviour of the investigated ceramics is rather of normal ferroelectrics with large thermal hysteresis. The transition temperature observed by means of differential scanning calorimetry measurements is in good agreement with that obtained from dielectric study.

Uniaxial Pressure Effect on Dielectric Properties of 0.7Na0. 5Bi0.5TiO3‐0.3SrTiO3 Ceramics

The 0.7Na0.5Bi0.5TiO3-0.3SrTiO3 ceramics were prepared by a solid-state mixed-oxide technique at 1180°C. X-ray diffraction and Raman spectroscopy studies revealed that the obtained samples possess perovskite structure. The behaviour of the electric permittivity (ɛ) and polarization of these ceramics as a function of uniaxial pressure (0 – 1000 bar) were investigated. Applying pressure shifts and decrease of maximum value of ɛ, a diffuseness of the permittivity characteristics, decrease of the thermal hysteresis and change of the polarization. We discuss our results based on elastic changes in inter-ionic distances in the crystal structure and nanoregions switching processes by pressure. The 0.7Na0.5Bi0.5TiO3-0.3SrTiO3 ceramics are expected to be a new promising candidate for lead-free electronic material.

Investigation of mechanical and electrical properties of Li doped sodium niobate ceramic system

ABSTRACT The Na0.96Li0.04NbO3 ceramic solid solution was prepared by means of a two-stage hot-pressing technology. The X-ray diffraction analysis showed the formation of a single perovskite phase with an orthorhombic symmetry in the investigated composition. The microstructure and EDS measurements were performed. They confirmed the high purity and the expected qualitative composition. A good homogeneity of the microstructures and a small degree of porosity were observed. The elastic modulus (the Youngs modulus E, shear modulus G, and Poissons ratio ν) of Na0.96Li0.04NbO3 were determined with the use of an ultrasonic method. The electrical properties of Na0.96Li0.04NbO3 ceramics were investigated at the frequency ranging from 0.5 kHz to 200 kHz, and the temperature ranging from room temperature to 750 K. The test sample shows a dielectric dispersion.

Raman and dielectric studies of 0.95Na0.5Bi0.5TiO3-0.05PbTiO3 ceramic

ABSTRACT 0.95Na0.5Bi0.5TiO3-0.05PbTiO3 ceramic was prepared by a conventional solid phase sintering process. X-ray diffraction analysis shows that the obtained specimens possess perovskite structure with rhombohedral symmetry. The microstructure study showed a dense structure, in good agreement with the relative density of above 95% as determined by the Archimedes method. The crystal structure, phase transitions behavior and dielectric properties of these ceramics were investigated. Relaxor-like behavior was revealed.

Dielectric and ferroelectric properties of NBT-BT systems

ABSTRACT The (1-x)Na0.5Bi0.5TiO3- xBaTiO3 ceramics (x = 0.1, 0.135 and 0.17) were fabricated by a conventional solid phase sintering process. The bulk density of the obtained samples exceeded 95% of the theoretical relative density as determined by Archimedes method. Dielectric and ferroelectric measurements of these ceramics were performed. Measurements of the ferroelectric properties show that, above the depolarization temperature Td, the shape of the hysteresis loops approaches that of linear dielectrics. The dielectric study results correlate with the hysteresis loops measurements. The relaxor-like behavior of the investigated materials was revealed.

Electrical transport in low-lead (1−x)BaTiO3–xPbMg1/3Nb2/3O3 ceramics

Low-lead (1−x)BaTiO3–xPbMg1/3Nb2/3O3 ceramics (x = 0, 0.025, 0.05, 0.075, 0.1, and 0.15) were prepared by the conventional oxide mixed sintering process, and their optical band gap, Seebeck coefficient, ac (σac) and dc (σdc) conductivities as a function of temperature were investigated for the first time. It was found that all samples have p-type conductivity. The low-frequency (20 Hz–2 MHz) ac conductivity obeys a power law σac~ωs, which is characteristic for disordered materials. The frequency exponent s is a decreasing function of temperature and tends to zero at high temperature. σac is proportional to ω0.07–ω0.31 in the low-frequency region and to ω0.51–ω0.98 in the high-temperature region. The temperature dependence of the dc conductivity showed a change in slope around the temperature at which the phase transition appeared. Both ac and dc conductivities showed a thermally activated character and possessed linear parts with different activation energies and some irregular changes. It was found that the hopping charge carriers dominate at low temperature and small polarons and oxygen vacancies dominate at higher temperature. (1−x)BaTiO3–xPbMg1/3Nb2/3O3 ceramics are expected to be promising new candidate for low-lead electronic materials.

Dielectric and ferroelectric properties of 0.82K0.5Bi0.5TiO3-0.18PbTiO3 ceramic: effect of uniaxial pressure

0.82K0.5Bi0.5TiO3-0.18PbTiO3 ceramic was fabricated by the mixed oxide method. An X-ray study shows that the obtained ceramic has a pure perovskite structure. The ϵ(T) and tanδ(T) show a peak centered at about 468 °C and 421 °C, respectively, and related to the tetragonal–cubic phase transition. The effect of uniaxial pressure (0–1500 bar) on dielectric and ferroelectric behavior of this ceramic was investigated. It was shown that uniaxial pressure significantly influences these properties. With the increasing pressure, (1) the maximum value of the electric permittivity and dielectric losses tanδ decreases and increases, respectively, (2) the peaks of ϵ and tanδ shift to higher temperatures, (3) the permittivity characteristics are smeared and the thermal hysteresis decreases, (4) hysteresis loops are smeared. The results were interpreted in term of domains (domains walls) change and de-aging process under the action of uniaxial pressure.

Sb Effect on Structural, Dielectric, and Ferroelectric Properties of Na0.5K0.5NbO3 Ceramics

Lead-free Na0.5K0.5(Nb1-xSbx)O3 (0<x<0.05) ceramics were fabricated by the solid-state reaction method and materials with more than 95% densification were obtained. A microstructure study confirms that the ceramics are well sintered. All compositions show complete perovskite solid solutions. Structural, dielectric and ferroelectric investigations for these specimens were performed. X-ray measurements showed that all compositions have a single perovskite structure with orthorhombic symmetry. Dielectric study revealed that the ceramics obtained are normal ferroelectrics. However some signs of diffuse phase transition were observed. The transition temperatures and the maximum electric permittivity were found to decrease and increase with increasing Sb content in the system, respectively, while ferroelectricity was enhanced significantly. A possible origin for these effects observed was discussed. The results could point to the possibility of application of Na0.5K0.5 (Nb1-xSbx)O3 as electronic ceramics.