Qingrui Yin

Ferroelectric and piezoelectric properties of (Na, K)0.5Bi0.5TiO3 lead free ceramics

(1 − x)Na0.5Bi0.5TiO3 − xK0.5Bi0.5TiO3 (NKBT100x; x being the mole ratio) piezoelectric ceramics were prepared by a conventional solid reaction method. The microstructure and ferroelectric properties of NKBT100x solid solution ceramics with compositions of Na0.5Bi0.5TiO3 (NBT)-rich and K0.5Bi0.5TiO3 (KBT)-rich were investigated by SEM, XRD, temperature dependence of dielectric constant, and hysteresis loop, respectively. XRD studies showed that the pure perovskite structure existed in NKBT100x ceramics with x ≤ 0.50, while a small amount of a second phase, K4Ti3O8, appeared in the ceramics with x ≥ 0.70 due to the structural instability of KBT-rich ceramics. The grain size decreased with increasing KBT content, showing that the KBT-rich solid solutions were very difficult to densify fully. The temperature dependence of the dielectric constant of NKBT100x ceramics showed that the depolarization temperature (Td) reached a minimum value at the composition of x = 0.16 (NKBT16) near the morphotropic phase boundary, which suggested that the ferroelectric state of co-existence between the rhombohedral phase of NBT and tetragonal phase of KBT were not as stable as the single phase of NBT and KBT, respectively. The poled density NKBT50 (x = 0.50) showed high piezoelectric properties, high Td and low dielectric loss, which was a good candidate for lead free piezoelectric ceramics working at relatively high temperatures.

Concentration quenching of Eu2+ in SrO·Al2O3:Eu2+ phosphor

Abstract The luminescence of Eu2+ in alkaline earth aluminates of the type SrO·Al2O3 has been studied. In SrO·Al2O3:Eu2+ phosphor, green Eu2+ luminescence is observed from Eu2+ on the two different strontium sites present in the lattice. Their concentration quenching processes of the two inequivalent Eu2+ ions are investigated, respectively, and the corresponding concentration quenching mechanism is verified as dipole-dipole interaction. The value of the critical transfer distance is calculated.

Hydrothermal synthesis of bismuth oxide needles

Bismuth oxide (Bi2O3) needles were fabricated hydrothermally by altering the starting materials, mineralizers, reaction temperature and time. The non-agglomerated Bi2O3 needles with a monoclinic structure were prepared using Bi(OH)3 in an alkali solution. The hydrothermal reaction took place at 120 °C in 0.5 h. The length and aspect ratio (length over diameter) of the needles are in the ranges of 6–70 and 5–16 μm, respectively. With the rising reaction temperature and time, the diameter of Bi2O3 needles increased, while the aspect ratio decreased. The formation mechanism of Bi2O3 needles is discussed in the paper.

Hydrothermal synthesis of Na0.5Bi0.5TiO3 fine powders

The effects of processing parameters on the growth and morphology of hydrothermally derived Na0.5Bi0.5TiO3 (BNT) powders were investigated. The BNT powders were synthesized in alkaline solution at temperatures of 160-220 degreesC from Ti(OC4H9)(4) and Bi(NO3)(3).5H(2)O compounds. Alkaline concentration had a great effect on the phase composition and morphology of the resultant powders. BNT phase was not obtained with NaOH concentrations lower than 0.5 or higher than 14 M. The morphology of BNT powders changed from spherical agglomerates to uniform cubic particles with NaOH concentrations in the range 2-12 M. The sizes of the cubic particles were about 3.5-5.5 mum with a typical Na0.5Bi0.5TiO3 structure

SrAl2O4: Eu2+, Dy3+ phosphors derived from a new sol-gel route

The SrAl 2 O 4 :Eu 2+ , Dy 3+ phosphor powders were prepared by a new sol-gel method using aluminum isopropoxide and strontium acetate as precursors. The sol-gel process and the structure of the phosphor powders were investigated by means of DSC-TG and XRD. It was found that the single-phase SrAl 2 O 4 was formed at 900 °C, which is 300 °C lower than that required for the conventional solid-state reaction. The particle morphology, photoluminescence and afterglow properties of the phosphors were studied in this article.

Effect of grain size on domain structures, dielectric and thermal depoling of Nd-substituted bismuth titanate ceramics

The microscopic origin of the grain size effects on the dielectric, piezoelectric, and thermal depoling properties of Aurivillius phase Bi3.15Nd0.85Ti3O12 was investigated. Using atomic force microscopy, domain walls were observed in micrometer grain size ceramics, but gradually disappeared with reducing grain size and were not found in ceramics with 90 nm grain size. In strain-electric field butterfly loops, the strain decreased with decreasing grain size indicating a decreasing contribution of non-180° domain walls switching to the strain. Lattice distortion (a−b)/b decreased with decreasing grain size. The thermal depoling resistance decreased with decreasing grain size, due to increasing internal mechanical stresses.

Influence of B 2 O 3 on Matrix Forming Process and Luminescent Properties of SrO • Al2 O 3 : Eu2 + Phosphor

The solid-state reaction process of SrO-Al 2 O 3 system with the nominal composition SrO:Al 2 O 3 = 1:1 (mol) has been investigated. A small amount B 2 O 3 can act as a flux to accelerate the forming of SrO.Al 2 O 3 host lattice and improve the luminescent properties of SrO.Al 2 O 3 :Eu 2+ phosphor. The fluxing role of B 2 O 3 is proved as the dopant B 2 O 3 can reduce the forming temperature of the reaction intermediate 3SrO.Al 2 O 3 and form the fusible borate to speed the reacting materials diffusion. Excessive B 2 O 3 will result in the forming of the impurity 4SrO.7Al 2 O 3 in the host lattice, which makes the emission intensity decrease and the emission wavelength shift to short wave.

Preparation of (Baxsr1-x)TiO3 sols used for ceramic film jet-printing

Abstract As one of the ways for solid free-form fabrication, jet-printing technique directly deposits the ceramic sols on a substrate to form ceramic films using a ink-jet printer. In this process, the properties of ceramic sols are the key to determine the printing effect. In this paper, Ba–Ti, Sr–Ti and Ba–Sr–Ti sols used for ceramic film jet-printing were prepared using barium acetate, strontium acetate and tetrabutyl titanate as starting materials. The properties of the sols were determined and adjusted successfully through the variation of processing parameters. Formamide was added into the sols to improve the stability and the viscosity of the sols. For a constant concentration of ethylene glycol, the stability of the sol increases and the viscosity of the sol decreases as the concentration of formamide increases. The concentration ratio of acetic acid to ethylene glycol R ac/eg is crucial to obtain stable sols for jet-printing process. The optimal R ac/eg value is 3:1 for Sr–Ti sols, 3:2 for Ba–Ti and Ba–Sr–Ti sols.

Concentration quenching of Eu2+ in SrO · 6Al2O3 : Eu2+ phosphor

In SrO · 6Al2O3 : Eu2+ phosphor, blue Eu2+ luminescence is observed from Eu2+ on the strontium site present in the lattice. The concentration quenching process between Eu2+ ions is determined and the corresponding concentration quenching mechanism is verified as dipole-dipole interaction. The value of the critical transfer distance is calculated as 25 Å and its reliability is confirmed by using Dexters theory on energy transfer.