K. Konieczny

Pyroelectric and dielectric study of NaNbO3 single crystals

Abstract The pyroelectric and dielectric properties as well as the hysteresis loops for NaNbO 3 single crystals were investigated. All the results obtained give evidence for the possibility of a ferroelectric state induced by an external electric field. This state disappears at ca. 280°C.

Electric Properties of (Na 0.5 Bi 0.5 ) 0.86 Ba 0.14 TiO 3 Single Crystal

Temperature dependence of electric permittivity, pyroelectric current, piezoelectric coefficients (d 33 and d 31 ) and electromechanical coupling factors (k 33 and k 31 ) of (Na 0.5 Bi 0.5 ) 0.86 Ba 0.14 TiO 3 single crystal have been measured. The presented crystal exhibits diffuse phase transition, ferroelectric properties, high piezoelectric coefficient (d 33 , 230 pC/N), and high electromechanical coupling factor (k 33 , 60%). These characteristics make this material interesting for applications.

LEAD-FREE (Na0.5Bi0.5)1-xBaxTiO3 SINGLE CRYSTALS (0 ≤ x ≤ 0.05) AND THEIR DIELECTRIC AND PYROELECTRIC PROPERTIES

ABSTRACT Lead-free single crystals of Na0.5Bi0.5TiO3-BaTiO3 (NBT-BT) system were prepared by Czochralski method and their dielectric and pyroelectric properties have been studied. The results were compared with these for pure NBT. The obtained samples show pure perovskite structure with rhombohedral symmetry at room temperature. Low frequency (100 Hz–100 kHz) investigations reveal the diffuse phase transitions. The obtained results are discussed in terms of local electric and strain fields caused by different ionic radius of (Na, Bi) and Ba ions. The NBT-BT system is expected to be a new promising candidate for lead-free electronic crystals.

Low-temperature heat capacity of NaNbO3 compound

Abstract The specific heat measurements of NaNbO3 crystals were carried out in the temperature range 4.5–278 K. The obtained data exhibit so-called non-Debye features at low temperatures and do not reveal any anomaly connected with antiferroelectric–ferroelectric phase transition. The experimental data are fitted and discussed with an expression containing the Debye and an Einstein contributions with ΘD=520, 612K and ΘE=183K for the low and high temperature phases, respectively. The presence of ≈T−2 term has been found in the lowest temperatures.

Uniaxial Pressure Effect on the Dielectric Properties of the BaTiO3 Single Crystals

Effect of the uniaxial pressure (0–1000 bars) on the dielectric properties of the BaTiO3 single crystals was studied. It was shown that the external stress significantly influences these properties. This includes shift of the phase transformation, diffuseness of the permittivity characteristics and reduction of the thermal hysteresis. These effects can be connected with a change in the domain structure, change of distances among the ions and change in the defect density under the action of external stress. Some thermodynamic parameters of the phase transformation were also evaluated. It was concluded, that the uniaxial pressure causes similar effects as the hydrostatic pressure.

Influence of Compressive Stress on Electric Properties of Na 0.5 − x K x Bi 0.5 TiO 3 Solid Solutions (x ≤ 0.1)

The dielectric, pyroelectric and hysteresis loops measurements of NBT-KBT ceramics for stress-free or under compressive stress (0-1500 bar) have been carried out. It was shown that compressive stress shifts of phase transition, reduction of thermal hysteresis and decrease of the polarization. These effects can be mainly connected with change in domain walls dynamics and with switch of the polarization under the action of stress.

Temperature and time changes electric permittivity in sodium niobate

Abstract Temperature and time dependencies of electric permittivity of sodium niobate have been measured. The dispersion and time changes of electric permittivity for NaNbO3 ceramic has been observed. Results of this investigations indicate for complex processes occuring in this material.

Dielectric and Ferroelectric Properties of Lead-Free NKN and NKN-Based Ceramics

Lead-free ceramics of Na0.5K0.5NbO3 (NKN), Na0.5K0.5(Nb0.94Sb0.06)O3 (NKNS6) and Na0.5K0.5(Nb0.94Sb0.06)O3 + 0.5%MnO2 (NKNS6 + 0.5%MnO2) have been prepared by a solid phase hot pressing sintering process. X-ray diffraction results show that the obtained samples possess the perovskite structure. The micrograph of the fractured surface showed a dense structure in a good agreement with that of 91–94% relative density determined by the Archimedes method. An average grain size decreases with Sb and Mn doping (from about 20 μm for NKN to about 5 and 2 μm for NKNS6 and NKNS6 + 0.5%MnO2, respectively). Low frequency (100 Hz–200 kHz) investigations revealed the diffuse phase transitions. It was found that Mn or Sb doping influence dielectric and ferroelectric properties. The pyroelectric and hysteresis loops measurements show that the samples are ferroelectric with a relatively large remanent polarization (18– 55 μC/cm2) and a low coercive field (7–10 kV/cm). The obtained results are discussed in the framework of foreign ions/lattice imperfections, which create local electric and elastic fields. The obtained materials are considered to be promising candidates for lead-free electronic ceramics.

Dielectric properties of Li0.003Na0.997NbO3 ceramics

Abstract Temperature, frequency and time dependencies of dielectric permittivity and pyroelectric current of Li0.003Na0.997NbO3 ceramics have been presented. Investigation of the pyroeffect reveals the existence of the local dipoles in a temperature range above the temperature of the maximum of the dielectric permittivity, Tm . The observed dispersion of the dielectric permittivity for this material and its time dependence, can be connected with the existence of these dipoles. The occurrence of these dipoles can be associated with a large local deformation accompanying the substitution of individual Li-by Na-ions and with imperfections of the polycrystal.

Effect of Ba addition on the structural, dielectric and ferroelectric properties of Na0.5Bi0.5TiO3 ceramics

Abstract Lead-free (Na0.5Bi0.5)1-xBaxTiO3 (x = 0, 0.04 and 0.06) ceramics were fabricated by conventional solid phase sintering process. X-ray diffraction analysis shows that obtained specimens possess the perovskite structure. The microstructure study shows a dense structure, in good agreement with the relative density determined by the Archimedes method (above 95 %). Electric permittivity anomaly is shifted to low temperature after Ba doping of NBT. The pyroelectric and hysteresis loops measurements show that polarization and coercive field increases and decreases, respectively, after Ba doping of NBT. The obtained results are discussed in terms of ions/lattice imperfections, which create local electromechanical fields. The investigated ceramics are considered to be promising candidates for lead-free electronic materials.