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The tuning of temperature stability in ultralow loss (Ba/Sr) zirconate microwave dielectric
(2022-01-01)
Pulphol, Phieraya
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Vittayakorn, Wanwilai
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Bongkarn, Theerachai
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Kolodiazhnyi, Taras
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Pongampai, Satana
The ceramic composition of Ba<inf>1-</inf><inf>x</inf> Sr <inf>x</inf> (Zr<inf>0.96</inf>Ga<inf>0.02</inf>Nb<inf>0.02</inf>)O<inf>3</inf>, where x = 0, 0.1, 0.2, 0.4, 0.5, 0.7, 0.9 and 1, was prepared and its crystal structure, microstructure, Raman and dielectric properties are analyzed. As revealed by powder x-ray diffraction analysis, the crystal structure transforms from cubic (Pm-3m) at 0 ≤ x ≤ 0.2 via tetragonal (Cmcm) at 0.2 < x ≤ 0.5 to orthorhombic (Pbnm) at x > 0.5. This is in agreement with the structural transformations previously reported for the Ba<inf>1-</inf><inf>x</inf> Sr <inf>x</inf> ZrO<inf>3</inf> and Ba<inf>1-</inf><inf>x</inf> Ca <inf>x</inf> ZrO<inf>3</inf> solid solution systems. Raman spectroscopy consistently supports these findings. The effects of structural distortion, grain size and density of samples on the microwave dielectric properties are discussed. With increasing Sr content from x = 0 to 0.2, the Q-factor of Ba<inf>1-</inf><inf>x</inf> Sr <inf>x</inf> (Zr<inf>0.96</inf>Ga<inf>0.02</inf>Nb<inf>0.02</inf>)O<inf>3</inf> ceramics drastically decreases from 18,000 to 3,000 at 10 GHz. The ceramics with a temperature coefficient of −1.4 ppm/K, dielectric constant of 37 and Q-factor of 2,900 at the resonant frequency f = 10 GHz was obtained at x = 0.5.
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Giant suppression of dielectric loss in BaZrO3
(2019-11-01)
Kolodiazhnyi, T.
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Pulphol, P.
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Vittayakorn, W.
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Vittayakorn, N.
We report the effect of precursor's purity and heterovalent substitution on the microstructure and dielectric properties of BaZrO<inf>3</inf> ceramics. We find that independent of the purity or raw materials, the dielectric loss of BaZrO<inf>3</inf> at microwave frequencies is rather high with a Q factor in the range of 1000–3000 at 10 GHz. All stoichiometric ceramics studied show up to three types of low-T dielectric relaxations in the 2–250 K range. All these dielectric anomalies can be suppressed by partial substitution of Zr for Nb. By alloying of BaZrO<inf>3</inf> with a hypothetical BaGa<inf>1/2</inf>Nb<inf>1/2</inf>O<inf>3</inf> phase the Q × f value of ceramics at microwave frequency can be improved significantly. The origin of this remarkable improvement is attributed to the effect of the donor ions on the random electric fields and antiferrodistortive instability. Ceramic with a chemical composition of BaZr<inf>0.96</inf>Ga<inf>0.02</inf>Nb<inf>0.02</inf>O<inf>3</inf> sintered at 1600 °C shows dielectric constant, ε′ = 36.7, temperature coefficient of the resonance frequency, τ<inf>f</inf> = +110 ppm/°C and Q × f = 172 THz.
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High piezoelectric activity in lead-free BaTiO3-BaZrO3-CaTiO3 ceramics with near polymorphic phase boundary
(2019-01-02)
Sutapun, Manoon
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Vittayakorn, Naratip
Lead-free 0.88BaTiO<inf>3</inf>–(0.12-x)BaZrO<inf>3</inf>–xCaTiO<inf>3</inf> (BT-BZ-xCT) ceramics were fabricated via solid state reaction. The effect of CaTiO<inf>3</inf> content on crystal structure, phase transition, and electrical properties was investigated systematically. The crystal structure and phase transition of ceramics were characterized by X-ray diffraction (XRD), Raman spectra and dielectric measurement. Results show that ceramic in the composition, x = 0.02, exhibits a rhombohedral structure. Ceramics with increasing CT content transformed from a rhombohedral to orthorhombic structure in the composition, x = 0.04, and eventually became a tetragonal structure at the composition, x ≥ 0.08. The polymorphic phase boundary (PPB) was observed at the composition, x = 0.06, with coexistence of orthorhombic and tetragonal phases showing at almost room temperature. This PPB composition exhibited a high piezoelectric response (d<inf>33</inf>*) of 1,150 pm/V at 10 kV/cm as an electric field was applied. These results indicate that the materials studied have potential as candidates for lead-free piezoelectric ceramics.
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The modification of surface, size and shape of barium zirconate powder via salt flux
(2019-01-01)
Charoonsuk, Thitirat
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Kolodiazhnyi, Taras
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Vittayakorn, Naratip
The “top-down” process via direct conversion of the micro (μm)-to-submicroscale (sub-μm) particle was applied in this work by using eutectic chloride salts to prepare BaZrO<inf>3</inf>. The particle size at optimum condition could be decreased by more than 10 times from 2.1 ± 0.9 μm to 168 ± 23 nm without destroying the 1:1 of Ba:Zr stoichiometry. The uniform sub-μm-BaZrO<inf>3</inf> powder was sintered in order to obtain ~98% dense ceramic at 1400°C/10 h, which is significantly lower than the 1650°C in normal cases. The microwave dielectric constant, tan δ, and quality factor were also determined. Furthermore, this method also was applied to lead-free piezoelectric material in the 0.87BaTiO<inf>3</inf>–0.13BaZrO<inf>3</inf>–CaTiO<inf>3</inf>(0.87BT–0.13BZ–CT) system. The particle size of 0.87BT–0.13BZ–CT was reduced greatly from >10 µm to 2.8 ± 0.4 µm. It can be proved that salt flux dissolution method enables high-purity with uniform sub-micro/nanometer powder production in one step by using simple laboratory equipment and low-cost raw materials.
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CaTiO3 induced ferroelectric phase coexistence and low temperature dielectric relaxation in BaTiO3–BaZrO3 ceramics
(2018-05-01)
Sutapun, Manoon
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Charoonsuk, Thitirat
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Kolodiazhnyi, Taras
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Vittayakorn, Naratip
The series of 0.86BaTiO<inf>3</inf>–(0.14−x)BaZrO<inf>3</inf>–xCaTiO<inf>3</inf> (abbreviated as BT–BZ–xCT) ceramics with 0.03 ≤ x ≤ 0.11 were studied to obtain high piezoelectric properties. Rietveld refinement analysis indicated that the BT–BZ–CT compositions follow a gradual rhombohedral (R) → orthorhombic (O) + R → O + tetragonal (T) → T phase transformation with increasing x. Clear evidence of the series of ferroelectric phase transitions was also found in the dielectric results. The R-O and O-T transition temperature shifted close to ambient temperature, while the Curie temperature slightly increased with increasing x. In addition to the dielectric loss peaks associated with the structural phase transitions, a broad low-temperature dielectric loss peak was detected in the R phase at T = 90-150 K. This dielectric relaxation was attributed to the domain wall freezing and fits well to the Vogel-Fulcher model with activation energy E<inf>a</inf> ≈ 60-300 meV and freezing temperature T<inf>VF</inf> ≈ 75-140 K. High piezoelectric strain coefficient (d<inf>33</inf>*) of about 1030 pm/V at 10 kV was achieved at x = 0.07, and a high Curie temperature (T<inf>C</inf>) was maintained at about 375 K.
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Soft-mechanochemical synthesis of monodispersed BaZrO3 sub-microspheres: Phase formation and growth mechanism
(2017-03-15)
Charoonsuk, Thitirat
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Vittayakorn, Naratip
Current technological and scientific challenges have encouraged the search for a simple and energy-efficient method to synthesis fine product particles with desirable morphology and properties. The submicro-spheres of perovskite barium zirconate (BaZrO<inf>3</inf>) in this study were synthesized successfully via the soft-mechanochemical method under ambient conditions, without surfactants or any capping agents. The synthetic mechanism model was proposed as being time-dependent. The hydrolysis, nucleation (crystallization) and growth of particles via Ostwald ripening were discussed deeply. Mechanical energy not only afforded a local high temperature to activate the chemical reaction and diffusion rate of particles, but also prevent aggregation and agglomeration by homogeneous mechanical stirring. Nevertheless, as-prepared BaZrO<inf>3</inf> powders exhibited properties of photoluminescence (PL) with green emission from lattice formation defects. Dielectric properties and the quality factor (Q-factor) were investigated as well. It was notable that the soft-mechanochemical method can provide a high yield and enable work that is environmentally friendly.
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High piezoelectric response in the new coexistent phase boundary of 0.87BaTiO3-(0.13-x)BaZrO3-xCaTiO3
(2015-12-05)
Sutapun, Manoon
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Vittayakorn, Wanwilai
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Muanghlua, Rangson
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Vittayakorn, Naratip
An investigation of the coexistent ferroelectric phase was carried out on the ternary system of 0.87BaTiO<inf>3</inf>-(0.13-x)BaZrO<inf>3</inf>-xCaTiO<inf>3</inf> [abbreviated as BT-BZ-xCT (where 0.00≤x≤0.13)]. Temperature-, frequency-dependent dielectric data, electric field-dependent strain and polarization as a function of composition are presented in order to understand the relationships of structure-properties and find the high piezoelectric response in this system. Results showed that ceramics in the composition range of 0.00≤x<0.04 were of a rhombohedral structure and transformed into a tetragonal structure at x>0.06. The multiphase coexistence of the rhombohedral and tetragonal phase in this system was identified at x=0.06. A large, virtually hysteresis-free electric field induced strain of 0.23% was achieved with the composition, x=0.06, at 40kV/cm on the boundary between rhombohedral and tetragonal phase. This relates to an extraordinarily high and normalized piezoelectric coefficient (S<inf>max</inf>/E<inf>max</inf>) of 1280pm/V, which was reached at a low electric field applied at 10kV/mm. These results indicated that a high piezoelectric response may stem primarily from the rhombohedral-tetragonal phase boundary, due to greater lattice softening and reduced energy barriers for polarized rotation.

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