Yu-Chuan Wu

Properties of Hexagonal Ba(Ti1-xMnx)O3 Ceramics: Effects of Sintering Temperature and Mn Content

The effects of sintering conditions on the densification, microstructural evolution and microwave properties of Ba(Ti1-xMnx)O3 ceramics were investigated in this study. For x0.25, densification is achieved at a temperature as low as 1250 °C. For x> 0.25, a significant densification starts only at temperatures above 1350 °C, owing to the existence of a Ba2Ti5O12 phase. X-ray photoelectron spectroscopy results manifest a change in the chemical state of Mn from Mn2+ to Mn4+ when the Mn content in the Ba(Ti1-xMnx)O3 ceramics is increased. A ≈0.9 wt % weight gain is obtained when Ba(Ti0.85Mn0.15)O3 powder is heated to 1500 °C, presumably owing to the transformation of Ba(Ti0.85Mn0.15)O2.85 to Ba(Ti0.85Mn0.15)O3, associated with the conversion of Mn2+ to Mn4+ as temperature increases. The microstructural evolution and microwave dielectric properties of the Ba(Ti1-xMnx)O3 ceramics are also affected by sintering temperature and Mn content. For Ba(Ti0.85Mn0.15)O3 ceramics, as a typical example, er varies from 52 to 60 and Qfr changes from 2,000 to 12,000 as sintering temperature increases from 1200 to 1500 °C. However, τf ranges from 200 to 250 ppm/°C, which is independent of sintering temperature.

Dissociation of basal dislocations in hexagonal barium titanate

Dislocation substructure in hot‐pressed hexagonal BaTiO3 ceramics was analysed by transmission electron microscopy. Two dislocation networks each consisting of dissociated half‐partials were determined for the Burgers vectors (b) using the g · b = 0 effective invisibility criteria, and the true directions (u) by trace analysis. Each of the networks contains three partial nodes that are in the form: 1/3[010]+1/3[100]+1/3[100]+1/3[100] = 0, where four partials meet at a point and the Burgers vectors are conserved, as analysed by the weak‐beam dark field technique. Basal dislocation with bb = 1/3<110> is dissociated into two prism plane half‐partials with bhp = 1/3<100> by: 1/3<110> → 1/3<010> + 1/3<100>. Dissociation of basal dislocation by a glide mechanism creates a stacking fault when shear occurs along <100> in the c‐layer of (000l), where l = 1, 3, 4 and 6, of the (chc)1(chc)2 (or (CBC)(ABA)) stacking sequence. The slip system of 1/3<110>(0001) in hexagonal BaTiO3 has been activated at 1300 °C by hot‐pressing under ∼25.8 MPa. Plastic flow contributing to the densification of hexagonal BaTiO3 ceramics occurs through glide of half‐partials in the basal plane by a glide‐controlled dislocation glide mechanism. Dislocation motion governed by the Peierls mechanism, where velocity is determined by both correlated and uncorrelated double‐kink nucleation on two half‐partials, is discussed.

Microstructures and Dielectric Properties of MgTiO3 Thick Film Prepared Using Aerosol Deposition Method

The aerosol deposition method (ADM) enables the deposition of films on a substrate at room temperature. In this study, we have focused on the effects of different gases and fluxes on the dielectric properties and microstructures of a MgTiO3 film. The crystal structures of the MgTiO3 film do not change with the gas and flux. The widths of the peaks on the X-ray diffraction patterns in the case of the MgTiO3 film are broader than that for the MgTiO3 raw powder; the surface roughness also increases with the gas flux. The fine grains are oriented randomly and are deformed by impaction; they stack alternately to form a lamellar structure. Polycrystalline MgO crystals are observed in between the MgTiO3 grains; they play an important role in enhancing the film formation. The capacitance remains constant with bias in the C-V curve. In the I-V curve, the leakage current is low at approximately 4 × 10−13 ∼ 5.5 × 10−12 A/cm2 and 3 × 10−12 ∼ 1.3 × 10−11 A/cm2 with gas fluxes of 3 L and 5 L, respectively.

Electrical Properties and Microstructural Analysis of Aliovalent-Ion (Y3+, Nb5+)–Doped Bismuth-Based Solid-Oxide Electrolyte

Bi1−x Nb x O1.5+δ (x = 0.15–0.25) and Bi1-y Y y O1.5 (y = 0.2–0.3) electrolytes were synthesized using solid-state reaction. The electrolytes have a δ-Bi2O3 structure and are stable at room temperature. A Bi0.8Y0.2O1.5 sample that was sintered at 950°C showed the highest conductivity of ∼1.97 S/cm at 800°C, while that of Bi0.85Nb0.15O1.5 + δ sintered at 950°C is 0.41 S/cm. The grain sizes of the Bi0.85Nb0.15O1.5+ δ and Bi0.8Y0.2O1.5 samples sintered at 950°C are ∼29.4 and 10.6 μm, respectively. The thermal expansion coefficients of the Bi0.85Nb0.15O1.5+ δ sample are 12.1 × 10−6/°C at 30–500°C and 22.3 × 10−6/°C at 500–800°C, while those of the Bi0.8Y0.2O1.5 sample are 15.4 × 10−6/°C at 30–500°C and 20.3 × 10−6/°C at 500–800°C.