Xiao-ming Chen

Origin of colossal permittivity in (In1/2Nb1/2)TiO2via broadband dielectric spectroscopy.

(In1/2Nb1/2)TiO2 (IN-T) ceramics were prepared via a solid-state reaction route. X-ray diffraction (XRD) and Raman spectroscopy were used for the structural and compositional characterization of the synthesized compounds. The results indicated that the sintered ceramics have a single phase of rutile TiO2. Dielectric spectroscopy (frequency range from 20 Hz to 1 MHz and temperature range from 10 K to 270 K) was performed on these ceramics. The IN-T ceramics showed extremely high permittivities of up to ∼10(3), which can be referred to as colossal permittivity, with relatively low dielectric losses of ∼0.05. Most importantly, detailed impedance data analyses of IN-T demonstrated that electron-pinned defect-dipoles, interfacial polarization and polaron hopping polarization contribute to the colossal permittivity at high temperatures (270 K); however, only the complexes (pinned electron) and polaron hopping polarization are active at low temperatures (below 180 K), which is consistent with UDR analysis.

Structure and dielectric property of Zr-doped (Na0.47Bi0.46Ba0.06K0.01)(Nb0.02Ti0.98)O3 lead-free ceramics

Abstract(Na0.47Bi0.46Ba0.06K0.01)(Nb0.02Ti0.98-xZrx)O3 lead-free ceramics (BNBKT-xZr, x = 0, 0.01, 0.02, 0.04) were synthesized via conventional solid state reaction method. Crystallite structure of the ceramics was studied using X-ray diffraction. The rhombohedral phase and tetragonal phase coexist in the BNBKT-xZr ceramics. The doping of Zr4+ into BNBKT lattice increases the percentage of the tetragonal phase. The size and shape of grains in the ceramics were affected by the doping of Zr4+ ions. For all the unpoled ceramics, two dielectric anomalies are observed in the dielectric constant-temperature curves. The maximum values of dielectric constant and corresponding temperatures change with the variation of Zr4+ amount. The doping of Zr4+ ions causes a decrease in the ferroelectric properties.

Preparation of homogeneous microstructure pure lead metaniobate by two-step sintering

The purpose of the present work is to obtain the Lead metaniobate ceramics with the orthorhombic phase via a two-step sintering method. The samples were first sintered at 1320°C for 10 min, and then sintered separately at 1260°C, 1220°C, and 1180°C for 4 h. All the ceramics show orthorhombic phase and homogeneous microstructure. It was found that the abnormal grain growth was restrained obviously.

Dielectric and piezoelectric properties of (Pb0.985-xBi2x/3La0.01)(Nb0.95Ti0.0625)2O6 ceramics

ABSTRACT (Pb0.985-xBi2x/3La0.01)(Nb0.95Ti0.0625)2O6 with 2 wt% excess PbO (x = 0, 0.01, 0.04, 0.06, 0.1) piezoelectric ceramics with high Curie temperature were fabricated via a conventional solid-state reaction method. Dielectric and piezoelectric properties of the ceramics were studied. The Curie temperatures of the ceramics decrease with the increase in the Bi3+ amount. The values of dielectric constant remain nearly unchanged from room temperature up to about 400 °C for the ceramics with x = 0, 0.01, 0.04 and 0.06. The ceramic with x = 0.04 possesses high piezoelectric charge constant (87 pC/N), low mechanical quality factor (22.60), low dielectric loss (0.024), and high Curie temperature (494 °C).

Microstructure and Dielectric Properties of 0.92Na0.5Bi0.5TiO3-0.06BaTiO3-0.02K0.5Na0.5NbO3-Based Ceramics Sintered in Oxygen and Nitrogen Atmospheres

The lead-free ceramics 0.92Na0.5Bi0.5TiO3-0.06BaTiO3-0.02K0.5Na0.5NbO3 and 0.92Na0.5Bi0.5TiO3-0.06BaTiO3-0.02K0.5Na0.5NbO3 with the addition of 0.2 wt% Co2O3 were prepared by using a solid state reaction method. The ceramics were sintered in O2 and N2 atmospheres, respectively. The rhombohedral-tetragonal morphotropic phase boundary exists in all samples, with the relative amount of tetragonal phase varying with the sintering atmospheres which does not affect grain size of the ceramics. In the dielectric constant-temperature curves for all samples, two dielectric anomalies appear. The phase transition temperatures and maximum values of dielectric constant are closely related to the sintering atmospheres. The mechanism was also discussed.

Hydrothermal synthesis of perovskite bismuth ferrite crystallites with the help of NH 4 Cl

Summary form only given. Multiferroics have attracted considerable attention recently because of their fascinating physical behaviors and potential applications. BiFeO3 is one of the well-known multiferroic compounds displaying coexistence of ferroelectricity and antiferromagnetism [1]. The BiFeO3 properties in nanosize were especially helpful for understanding the foundational ferroelectric and magnetic mechanism [2]-[4]. Recently, only a few approaches by the hydrothermal method were reported about the pure BiFeO3 with irregular shapes [5],[6]. The bismuth ferrite powders in these works were synthesized by using [Bi(NO3)3-5H2O] and [Fe(NO3)3-9H2O] as start materials, which reacted to produce pure BiFeO3 phase in a limited experimental range. In this paper, pure BiFeO3 crystallites were synthesized by using FeCl3-6H2O and BiCl3 as start materials and NH4CI as an addition in wide hydrothermal conditions. Bismuth ferrite powders were prepared via a hydrothermal process using a stoichiometric mixture of FeCl3-6H2O and BiCl3 as metal precursors and NaOH as a mineralizer. FeCl3-6H2O and BiCl3 kept the resultant concentration 0.05 M were dissolved in distilled water under a mechanical stirring. NaOH solution was slowly added to the above solution, followed by adding 1.29 g (1 M) NH4CI to part samples. Finally, the brown suspension was transferred into a 29 mL Teflon vessel filled at 4/5 of its volume. The hydrothermal treatment was performed with different reaction temperatures and holding times. After cooling down to room temperature, the products were washed several times and dried in an oven at 70 °C. X-ray diffraction (XRD) analysis was performed to determine the powder phases. Scanning electron microscopy (SEM Quan200) was employed to investigate the particle sizes and morphologies of the products. The magnetic properties of part samples were measured with an LDJ9600 type of vibrating sample magnetometer (VSM). The pure BiFeO3 phase can be synthesized at wide NaOH concentration and wide temperature range with the help of NH4Cl solvent as shown in Fig. 1 and 2. The BiFeO3 morphologies change from agglomerate and irregular particles to regular and dispersive cubic particles, and more morphologies were obtained with the help of NH4CI solvent as shown in Fig. 3 and 4. BiFeO3 sample with more compact particles shows relative higher saturation magnetization. The details will be reported in the full manuscript.

Microstructure, depolarization temperature, and piezoelectric properties of (Bi0.5Na0.4K0.1)Ti0.98M0.02O3-δ (M3+ = Al3+, Fe3+) lead-free ceramics

ABSTRACT (Bi0.5Na0.4K0.1)Ti0.98Al0.02O3-δ (BNKT-A) and (Bi0.5Na0.4K0.1)Ti0.98Fe0.02O3-δ (BNKT-F) ceramics were prepared via a conventional solid-state reaction method. Microstructure and piezoelectric properties of the two ceramics were comparatively studied. Both the samples exhibit single-phase structures. There is no obvious change in microstructure between the two samples. The depolarization temperatures were estimated from dielectric spectra, change of piezoelectric constant with annealing temperature, and thermally stimulated depolarization current. Compared with BNKT-A, BNKT-F exhibits higher piezoelectric constant and higher depolarization temperature. The Rayleigh analysis exhibits that BNKT-F has higher extrinsic contribution from irreversible domain wall translation process compared with BNKT-A.