Structure and dielectric properties of high-pressure perovskite-type oxyfluorides xKTiO2F–(1−x)BaTiO3

10% KF-doped barium titanate powders, Ba0.9K0.1TiO2.9F0.1, were synthesized through a sol–gel process. The powders, calcined at 650 °C, consist of cubic crystalline particles of ∼70 nm in length; the particle size increases to ∼200 nm as the firing temperature increases to ca. 800 °C, above which F2 begins to evaporate. Dense ceramics were fabricated by the spark plasma sintering (SPS) method; the average grain size is ∼2 µm in lengths. The ceramics, well annealed at 1,000 °C in an O2 gas flow, have good dielectric and piezoelectric properties; the piezoelectric d 33 value is 230 pC/N at room temperature. At the ferroelectric Curie temperature T C = 47 °C, the dielectric constant and loss tan δ are 10,000 and <5% at 10 kHz, respectively. The Curie–Weiss relation holds in the fully disordered cubic and ordered rhombohedral phases, showing the second order 1:2 relation. Below 10 kHz, large dielectric dispersion caused by a domain-wall motion appears at the temperature range of -50 to 107 °C. Some discussions are made for these dielectric properties of the ceramics.

Section: Introductionmentioning

confidence: 99%

Dielectric and Piezoelectric Properties of 10% KF-Doped BaTiO₃ Ceramics

Akishige

Hiraki

Tsukada

et al. 2010

“…7) Thus, the solid-state synthesis under high pressure was carried out to prevent F À from evaporating, and dense ceramics were fabricated. 8) The grains show a size of $2 mm, which is too large to express good piezoelectricity. Very recently, we have synthesized KF-BT/0.10 ceramics by the spark plasma sintering (SPS) method.…”

Section: Introductionmentioning

confidence: 99%

Synthesis and Electrical Properties of KF-Doped BaTiO₃ Ceramics

Akishige

Honda

Tsukada

2010

KF-doped barium titanate ceramics, Ba1-x K x TiO3-x F x (KF-BT/x: 0≦x≦0.15), were fabricated by spark plasma sintering (SPS) using fine particles prepared by a sol–gel method. We measured the dielectric and piezoelectric properties of the SPS ceramics after annealing in an O2 gas flow at 1273 K. The dielectric constant and the piezoelectric constant d 33 were enhanced in KF-BT/0.10, as found in the single crystals, because the composition of x=0.10 locates near the tricritical point (TCP). However, some different behaviors from those of the single crystals were found; in particular, T C of the ceramic forms is much higher than that of the crystalline forms, and the difference becomes marked with increasing x. We consider that the evaporation of F-, which occurs during the O2 annealing process, markedly increases T C.

“…3,4) Moreover, Katsumata et al successfully synthesized KF-doped BaTiO 3 ceramics with contents from x ¼ 0 to 1 at high pressures and high temperatures, and found relaxor behavior at around x ¼ 0:15. 5) According to Bao et al, KF-flux-grown BaTiO 3 single crystals contain not only the acceptor impurity K þ but also the anion donor F À at high concentration; on the other hand, the crystals annealed at 1,273 K in air contain mostly K þ as a result of F À evaporation and show clear aging effects. 6) Therefore, it is interesting to investigate the physical properties of the KF-doped BaTiO 3 , especially the crystals with a KF content near the TCP.…”

Section: Introductionmentioning

confidence: 99%

Piezoelectric Properties near the Tricritical Point on KF-Doped BaTiO₃Single Crystal

Akishige¹,

Hiraki²

2009

The temperature dependence of the piezoelectric constant d 33 , electromechanical coupling factor k 33 , dielectric constant " T 33 and elastic compliance s E 33 for a single crystal of KF-doped barium titanate with a KF content near the tricritical point (TCP), Ba 0:91 K 0:09 TiO 2:91 F 0:09 (KF-BT/0.09), was measured by a resonance-antiresonance method in a temperature range between 270 and 340 K. The single crystals used were grown by a KF-flux method and the largest single crystal was a cube of 5 mm size. A large piezoelectric constant and a large dielectric constant were obtained at 300 K: d 33 ¼ 300 pC/N, k 33 ¼ 0:59, and " T 33 ¼ 3;000. As the temperature increases, " T 33 gradually increases toward T C but does not show any discontinuous changes at T C ¼ 329 K; moreover, s E 33 and d 33 increase with temperature between 270 and 310 K. However, above 310 K, they decrease toward T C . The fluctuation of the order parameter near the TCP induces these peculiar behaviors.