Ilze Smeltere

Ultrasonication as a Method of Investigation of the Mechanical Properties of Doped Hafnium Barium Titanate

The purpose of this study was to fabricate dense ceramic specimens from the system of BaTiO3-BaHfO3 and then to perform mechanical tests. The effect of Hf content on a microstructure and mechanical properties of the BaTiO3-BaHfO3 solid solution was investigated at room temperature. To determine the elastic constants (the Young′s modulus E, the shear modulus G, bulk modulus K and the Poisson′s ratio v) of BaHfxTi1-xO3 a method of measurement of the longitudinal (VL ) and transverse (VT ) ultrasonic wave velocities for this type of material was developed.

SYNTHESIS AND CHARACTERIZATION OF SB-SUBSTITUTED (K0.5Na0.5)NbO3 PIEZOELECTRIC CERAMICS

ABSTRACT Lead-free piezoelectric ceramics (K0.5Na0.5)(Nb1-xSbx)O3+0.5 mol.%MnO2, where x = 0 ÷ 0.10, with single phase structure and rhombohedral symmetry at room temperature were prepared by conventional ceramic technology. The optimal sintering temperatures of compositions were within 1100°–1140°C. MnO2 functions as a sintering aid and effectively improves the densification. The samples reached density from 4.26 g/cm3 for undoped (K0.5Na0.5)NbO3 to 4.40 g/cm3 for Mn/Sb5+ co-doped ceramics. The co-effects of MnO2 doping and Sb5+ substitution lead to significant improvement in dielectric and piezoelectric properties: ϵ at the Tc increased from 6000 (KNN) to 12400 (x = 0.04), d33 = 92 ÷ 192 pC/N, kp = 0.32 ÷ 0.46, kt = 0.34 ÷ 0.48.

Dielectric Properties of Na0.5K0.5(Nb1-xSbx)O3+MnO2 Ceramics (x = 0.04, 0.05 and 0.06)

Lead-free ceramics Na0.5K0.5(Nb1-xSbx)O3+0.5mol%MnO2 (x = 0.04, 0.05 and 0.06) were prepared by conventional sintering and hot pressing process; their microstructure and dielectric properties have been studied. It is found that increase of sintering temperature promotes the obtaining highly dense microstructure and increase in grain size while doping with Sb contributes to more dense and homogeneous microstructure and smaller grain size. Low frequency (100 Hz-200 kHz) investigations revealed the diffuse phase transitions. It can be concluded from experimental results that Sb doping improves dielectric properties. The obtained materials are expected to be promising candidates for lead-free electronic ceramics.

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.

SINTERING OF LEAD-FREE (K0.5Na0.5)NbO3 BASED SOLID SOLUTION

ABSTRACT In this study lead-free solid solution (K0.5Na0.5)NbO3 was prepared, structure, dielectric parameters of ceramics were investigated. The doping of sintering aids did not affect the crystallographic structure of the ceramics significantly; all ceramic samples had a single-phase perovskite structure. Added elements CdO, ZnO, MnO2, V2O5 effectively decreased the sintering temperature of KNN by 50°–80°C. All sintering aids influenced sinterability, microstructure and dielectric properties of ceramics. Dielectric constant for doped samples increased from 6000 up to 8000; Pr = 15 μC/cm2, Ec = 9 kV/cm, d33 = 110 pC/N, kp = 0.38 and Qm = 190 for MnO2 doped samples.

Characterization of Dielectric Anomaly in Solid Solution Based on BaTiO3

The influence of Zr doping on a structure and dielectric properties of Ba0.8Sr0.2TiO3 were studied. For this purpose Ba0.8Sr0.2Ti0.75Zr0.25O3 ceramics were obtained by a conventional method and were determined by an X-ray diffraction (XRD) and scanning electron microscopy (SEM) for crystallographic, surface morphological and compositional studies. The temperature and frequency dependence of dielectric permittivity were studied in the temperature range from 150 to 500 K and the frequency between 20 Hz and 1000000 Hz. The thermal behavior of the Ba0.8Sr0.2Ti0.75Zr0.25O3 ceramics were also studied using Differential Scanning Calorimetry. A diffusivity coefficient γ was calculated.

Effect of Variable Valence Ion Doping on the Dielectric Properties of BaTiO3–Based Materials

Dielectric properties of BaTiO3, BaTiO3 + 0.1 wt.% Fe2O3 and BaTiO3 + 1 wt.% Fe2O3 ceramics were studied. The dielectric measurements were performed at the temperature ranging from 130 K to 500 K and at the frequency ranging from 0.1 Hz to 10 MHz. Phase transitions were also determined by a thermal analysis in a wide temperature range. Both thermal analysis and electrical characterization techniques show that the temperature of phase transition is shifted towards lower temperatures with increasing Fe2O3 content. The changes and diversity of the observed phase transition temperatures occurred as a consequence of the ion substitution. Such behaviour of the investigated polycrystalline materials may be due to the multivalence nature of the incorporated ions.

Dielectric Response in (K0.5Na0.5) (Nb1-xSbx)O3+0.5 mol%MnO2 Ceramics to Weak Sinusoidal Fields of Low and Infra-low Frequencies

The thermal anomalies exhibited as “shoulders” at infra-low frequencies and maximums at low frequencies related to structural transitions in the polar phase of (K0.5Na0.5)(Nb1-xSbx)O3+0.5 mol%MnO2 are found to shift from T ∼ 185°C to T ∼ 140°C at changing concentration x from 0 to 0.05. The range of temperature ΔТ(х) corresponding to the difference between positions of the anomalies on the ϵ′(T) curve at frequencies 1000 Hz and 1 Hz changes from 0.5 degrees at x = 0 to 2.5 degrees at x = 0.05, which may point to relaxor properties of the given phase transition being present only at rather high concentrations of Sb.

Influence of BaTiO 3 on synthesis and structure of lead-free ceramics based on KNN

In the present work lead-free compositions with a stoichiometric formula (1-x)(K_0.5Na_0.5)Nb_1-ySb_yO₃-xBaTiO₃ (x=0.01, 0.02, 0.04; y=0.04, 0.07) were produced by solid state sintering method. Manganese oxide MnO₂ was used as a dopant in order to lower the sintering temperatures. The influence of BaTiO₃ on the microstructure, density, mechanical and electrical properties of Sb-substituted KNN ceramics was investigated. X-ray diffraction analysis revieled pure perovskite structure. Microstructural investigation of the ceramics samples showed homogeneous structure with a slightly rounded cubical grain shape. Phase transition temperature T_c is shifted to lower temperatures in comparison to Sb-substituted KNN ceramics. Phase transition peak at T_c becomes broader indicating the diffuse phase transition.

Synthesis and dielectric properties of modified potassium sodium niobate solid solutions

In the present work processing microstructure and dielectric properties of lead free KNN based ceramics have been studied. Compositions with a stoichiometric formula (1 − x)(K0.5Na0.5)Nb1 − ySbyO3-xBaTiO3 (x = 0.01, 0.02, 0.04; y = 0.04, 0.07) were produced by solid state sintering method. The addition of manganese oxide MnO2 after synthesis promoted the sintering and densification of ceramic samples. The influence of BaTiO3 on the microstructure, density and electrical properties was investigated. X-ray diffraction analysis confirmed that obtained samples had a pure perovskite structure with no traces of secondary phase. Phase transition peak at Tc is broad indicating the diffuse phase transition.