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Abstract: Dielectric and magnetic properties of the xBiFeO3–yDyFeO3–zBaTiO3 solid solution ceramics at high temperature range of RT ∼600°C have been characterized. For the more detailed understandings of the multiferroic property, the relation between the crystal structure transition, magnetic transition, dielectric transition with increasing temperature have been analyzed. Residual magnetization M r under the low and high applied magnetic fields (H =20Oe, 8kOe) and the dielectric properties, ɛ r and tan δ, with varying measuring frequency and temperature have been characterized using the vibrating sample magnetometer and LCR meter, respectively. The neutron diffraction data has been collected at the temperature range of RT ∼800°C. The low DyFeO3 concentration samples (y =0, 0.025) show the magnetic transitions at temperature range of 410–430°C, while the high DyFeO3 samples (y ≥0.05) show the additional transition at 250–290°C. The magnetic transition at 410–430°C corresponds to the crystal structural transition to the tetragonal P4mm from the rhombohedral R-3c, at which the BiFeO3 and the DyFeO3 samples lose their antiferromagnetic ordering. [Copyright &y& Elsevier]

Crystal structure, ferromagnetic and electric polarizations have been characterized for attaining the ferroelectromagnetic materials in the ternary and binary solid solutions consisting of ferroelectric and antiferromagnetic end members: BiFeO3(BF), PrFeO3(PF), NdFeO3(NF), BaTiO3(BT),and PbTiO3(PT). The XRD and neutron diffraction data collected in the temperature range 10–300 K have been analyzed by the Rietveld refinement method. Every prepared sample shows weak ferromagnetization with a maximum remanent magnetization Mr=0.5 emu/g in the 0.8BiFeO3–0.2BaTiO3. The 0.2BF–0.2NF–0.6PT(0.0075 mol Ta2O5), 0.8BF–0.2BT, and 0.2BF–0.2PF–0.6PT(0.0075 mol Ta2O5) having the noncentrosymmetric structure I4cm (a=b≒0.54 nm, c≒0.78 nm) show a ferroelectricity with remanent polarization Pr=1.2–3 μC/cm2. [Copyright &y& Elsevier]

The thin film phosphors of SrTiO3:(0.004 mol Pr, 0.02 mol Ga) have been prepared by chemical solution deposition (CSD) method on the SiO2/Si, alumina, and quartz substrates. The phase formation and photoluminescence (PL) property of thin films with crystallization temperature have been characterized by FE-SEM, XRD, and spectrophotometer. The SrTiO3 (ST) phase was formed from 600 °C regardless of the type of substrate. The emission peak (611 nm) and excitation peak (370 nm) from the thin films were similar to those of the powder sample prepared by solid-state reaction. The SiO2/Si substrate produced the strongest emission and excitation spectra. [Copyright &y& Elsevier]

The effect of calcination process on a phase evolution, a microstructure development and the piezoelectric properties were investigated in 0.75BiFeO 3 -0.25BaTiO 3 (0.75BF-0.25BT) ceramics. At the relatively low calcination temperatures of 600 °C–650 °C, a Bi 25 FeO 40 impurity phase was formed in addition to some unreacted raw materials and a perovskite phase. As the calcination temperature increased to the range of 700–900 °C, other intermediate phase BaBi 4 Ti 4 O 15 was formed concurrently with small amounts of unreacted BaCO 3 and perovskite matrix phase. At 950 °C a pure single perovskite phase of 0.75BF-0.25BT solid solution was observed. The sintered samples produced by using the raw powder calcined at a relatively low temperature of 600–900 °C showed a large fraction of pseudo-cubic relaxor phase (0.54–0.71 mass fraction) with the rest of a rhombohedral ferroelectric phase. They showed poor piezoelectric properties at sintering temperature below 1000 °C due to the nonuniform compositional distribution of the calcined powder. The homogeneous calcination at 950 °C for 2 h reduced greatly the optimum sintering temperature and significantly enhanced piezoelectric properties in the BF-BT ceramics. High Curie temperature as well as high piezoelectric properties were obtained at the sintering temperature as low as 920 °C: k p = 0.361, d 33 = 123 pC/N and T C = 653 °C in the 0.75BF-0.25BT ceramics and k p = 0.337, d 33 = 183 pC/N and T C = 525 °C in the 0.7BF-0.3BT ceramics. This low temperature sintering of the BF-BT ceramics by a homogeneous calcination could be applied to the fabrication of the lead-free multi-layer piezoelectric devices with inexpensive internal electrodes. [ABSTRACT FROM AUTHOR]

Abstract The structural origin of the negative coefficient of thermal expansion (CTE) along the c-axis in cordierite is investigated using high temperature X-ray diffraction. The evolution of the lattice parameters, bond length, covalent character, and electron density distributions are analyzed with increasing temperature. The increase of covalent character of the tetrahedral bonds in the six-membered hexagonal ring is considered as the possible origin for the negative expansion. In addition, the bridging oxygen can act as a buffer absorbing thermal energy and prevents the increase in M1-O-M2 bond. The electron density distribution indicates that the linking oxygen strongly vibrates transversely across two coordinate M1-O-M2 linkages. The CTE and pore size and distribution change drastically at near 1300 °C due to the substantial increase in cordierite phase proportion and the formation of a liquid phase. Raw materials are consumed completely at 1450 °C and the CTE decreases to 1.3 ppm K−1. [ABSTRACT FROM AUTHOR]

Indialite/cordierite (Mg 2 Al 4 Si 5 O 18 ) glass ceramics have been reported to show excellent millimeter-wave dielectric properties of low dielectric constant of 4.7 and high quality factor Qf of >200,000 GHz when crystallized at the temperature range of 1200–1300 °C. The glass ceramics were crystallized to the intermediate indialite phase at 1200 °C, which phase was then transformed to the stable cordierite phase as crystallization temperature increased. In this paper, the crystallization procedure of the glass with pure cordierite composition was clarified by macro difference thermal analysis (DTA) and X-ray powder diffraction (XRPD) patterns. The crystallization of the glass occurred in two steps above the T g of 778 °C: the 1st step is the formation of β -quartz solid solutions (s. s.) at 919 °C, and the 2nd step is the transformation from β -quartz s. s. to indialite at 946 °C. As increasing the crystallized temperature, indialite phase converted to cordierite. This phenomenon indicates that indialite is an intermediate phase during the crystallization process from glass to cordierite. [ABSTRACT FROM AUTHOR]

High-porosity cordierite ceramics were sintered in two different atmospheres, that is, in air (oxidizing) or in double-enclosed crucibles (mildly reducing). Paste slurries of cordierite compositions mixed with organic binders and pore formers were extruded into honeycomb-type substrates to produce diesel particulate filters (DPFs). The present study was conducted to explore the effects of sintering atmosphere on pore size, crystallization, amorphous phase, and thermal expansion coefficient (CTE) of sintered DPF honeycombs. Crystal phases were quantitatively analyzed using the Rietveld refinement method using powder X-ray diffraction (XRD) data. Amorphous phases were quantified using the Rietveld-internal standard method, and their presence was qualitatively confirmed by high-resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED) analysis. The most notable features observed were a dramatic decrease in the pore-size distribution and an enhanced rate of cordierite/indialite phase crystallization when sintering was performed in a double-enclosed crucible. A relatively high concentration of carbon monoxide (CO) in the double-enclosed crucible reduced the liquid-phase viscosity. This low-viscosity liquid phase spread relatively easily on the surfaces of crystal phases and enhanced the crystallization rate owing to a relatively large liquid–solid contact area in the mildly reducing atmosphere. The higher CTEs of DPFs produced in air compared with those produced in enclosed crucibles are discussed in relation to the amounts of amorphous and crystal impurity phases and crystal texture. [ABSTRACT FROM AUTHOR]

Indialite/cordierite (Mg 2 Al 4 Si 5 O 18) glass-ceramics with a low dielectric constant of 4.7 and a high Qf of >200 × 103 GHz are predicted for use as micro/millimeter-wave materials in the fifth generation (5G) mobile communication systems. The glass-ceramics have a serious cracking problem caused by the anisotropic crystal growth during the surface crystallization. In this paper, the cracking was prevented by adding TiO 2 which acts as a seed. The glass-ceramics produced without cracking were composed of spherical crystals of approximately 10 μm diameter, formed by volume crystallization. Precipitated phases of the glass-ceramics crystallized at 1200–1350 °C/10 h and 20 h were indialite, cordierite, Al 2 TiO 5 and rutile. The glass-ceramics crystallized for 10 h were analyzed by the Rietveld method. Indialite precipitated as an intermediate metastable compound at the lower temperature of 1200 °C and transformed to cordierite at the crystallization temperature. The reaction between cordierite and TiO 2 produced the new Al 2 TiO 5 phase. The amounts of Al 2 TiO 5 and rutile affected the microwave dielectric properties. In particular, the amount of rutile affected the TCf. In the cases of 10 wt % added TiO 2 , and the crystallized at 1250 °C for 10/20 h the TCf values were improved to -2/-8 ppm/°C. [ABSTRACT FROM AUTHOR]

Crystal structures and piezoelectric properties of PbZrO 3 -PbTiO 3 -Pb(Ni 1/3 Nb 2/3)O 3 ceramics near the triple point composition, particularly characteristics of the pseudocubic phase, were investigated. The pseudocubic phase, which formed near the triple point composition, disappeared with increase in the PbZrO 3 content. The pseudocubic phase had the Pm3m cubic structure. The tetragonal-pseudocubic morphotropic phase boundary (MPB) structure was developed during the tetragonal-to-cubic phase transformation. However, the rhombohedral phase directly transformed to the cubic phase because the structure of pseudocubic phase was similar to the rhombohedral structure. The specimens with pseudocubic phase and the specimens near pseudocubic phase exhibited nano-sized domains and small coercive electric fields, revealing their low domain wall energies. These specimens exhibited second-order ferroelectric-to-paraelectric phase transition and low Curie temperatures, confirming their low domain wall energies. The enhanced dielectric and piezoelectric properties of these specimens could be attributed to their low domain wall energies. [ABSTRACT FROM AUTHOR]

Abstract CuO-added (1-y)(Na 0.5 K 0.5)(Nb 1-x Sb x)-yCaTiO 3 ceramics with 0.0 ≤ x ≤ 0.1 and 0.04 ≤ y ≤ 0.055 were sintered at 970 °C. Various cubic-based polymorphic-phase-boundary (PPB) structures were formed: orthorhombic-tetragonal-cubic, and tetragonal-cubic PPB structures. The crystal structure of the specimens near Curie temperature is a mixture of Pm3m cubic and P4mm tetragonal structures and these ceramics showed ferroelectric properties. A schematic phase diagram of these ceramics has been suggested. The piezoelectric properties of these specimens were influenced by their crystal structure. All the specimens are expected to have good fatigue properties. In particular, the specimen with a tetragonal-cubic PPB structure (x = 0.04 and y = 0.045) has a large d 33 of 338 pC/N and a high strain of 0.17% at 4.5 kV/mm. This specimen has good temperature stability; a d 33 value of 300 pC/N and strain of approximately 0.12% were obtained at 175 °C, indicating that this specimen is a good candidate for use as a piezoelectric multilayer actuator. [ABSTRACT FROM AUTHOR]

Abstract: The influence of processing parameters on phase formation and particle size of hydrothermally synthesized BiFeO3 powders was investigated. BiFeO3 powder was synthesized by dissolving bismuth nitrate and iron nitrate in KOH solution at temperatures ranging from 150 to 225°C. X-ray diffraction patterns and scanning electron microscopy observation indicated that rod-like α-Bi2O3 phase was formed at initial stage of reaction and dissolved into ions to form thermodynamically stable BiFeO3 phase. Single-phase perovskite BiFeO3 has been formed using a KOH concentration of 8M at a temperature of ≥175°C in a 6h reaction period. BiFeO3 particle growth was promoted by lowering the KOH concentration, or increasing the duration time or reaction temperature. The effects of processing conditions on the formation of crystalline BiFeO3 powders were discussed in terms of a dissolution–precipitation mechanism. The magnetization of the BiFeO3 powders at room temperature showed a weak a ferromagnetic nature. [Copyright &y& Elsevier]

Abstract: The biaxial textures of MgO thin films with thicknesses 4500–5500Å deposited by electron beam evaporation on glass substrates have been characterized. The surface normal to the amorphous soda-lime glass substrate was placed parallel to the MgO vapor flux, i.e., at zero degree with respect to the MgO vapor source. The MgO thin films showed biaxial texture regardless of the deposition parameters. XRD and SEM have been used to characterize the crystal structure and thin film surface morphology. In this study we devised a novel method for the characterization of the biaxial texture of MgO thin films with thicknesses ≤5000Å, for which the X-ray pole figure method cannot be used due to the low scattering intensity from the MgO film containing only low atomic X-ray scattering ions. We report the biaxial texture development in MgO thin films grown by E-beam evaporation on the amorphous glass substrate inclined at zero degree with respect to the MgO vapor source. [Copyright &y& Elsevier]

Abstract: In this article, photoluminescence of Pr3+ ions in the double tungstate A(M1−X Pr X )W2O8 (A=Li, Cs, M=Al, Sc, La; 0.0≤ X ≤0.1) are characterised. By varying ion radius in A and M sites the crystal structure was modified and even in crystals with similar structural characteristics three distinctive types of luminescence are observed. When the substitution ions in both A and M sites are relatively small the host lattice exhibits luminescence dominantly. With the small A site ion (Li+) and the large M site ion (La3+, 1.03Å) the Pr3+ ion exhibits prominent luminescence. With the very large A site ion (Cs+, 1.67Å) and relatively small M site ion (Sc3+, 0.75Å) the Pr3+ exhibits both the 4f2–4f5d excitation and the 3P J manifold excitations in the absorption spectrum. These excitation levels lead to two strong emissions from the Pr3+. PL characteristics are discussed with respect to crystal structural criteria. [Copyright &y& Elsevier]