Linghang Wang

Microstructure and dielectric properties of (Nb + In) co-doped rutile TiO2 ceramics

The (Nb + In) co-doped TiO2 ceramics recently attracted considerable attention due to their colossal dielectric permittivity (CP) (∼100,000) and low dielectric loss (∼0.05). In this research, the 0.5 mol. % In-only, 0.5 mol. % Nb-only, and 0.5–7 mol. % (Nb + In) co-doped TiO2 ceramics were synthesized by standard conventional solid-state reaction method. Microstructure studies showed that all samples were in pure rutile phase. The Nb and In ions were homogeneously distributed in the grain and grain boundary. Impedance spectroscopy and I-V behavior analysis demonstrated that the ceramics may compose of semiconducting grains and insulating grain boundaries. The high conductivity of grain was associated with the reduction of Ti4+ ions to Ti3+ ions, while the migration of oxygen vacancy may account for the conductivity of grain boundary. The effects of annealing treatment and bias filed on electrical properties were investigated for co-doped TiO2 ceramics, where the electric behaviors of samples were found to...

Piezoelectric activity in Perovskite ferroelectric crystals

Perovskite ferroelectrics (PFs) have been the dominant piezoelectric materials for various electromechanical applications, such as ultrasonic transducers, sensors, and actuators, to name a few. In this review article, the development of PF crystals is introduced, focusing on the crystal growth and piezoelectric activity. The critical factors responsible for the high piezoelectric activity of PFs (i.e., phase transition, monoclinic phase, domain size, relaxor component, dopants, and piezoelectric anisotropy) are surveyed and discussed. A general picture of the present understanding on the high piezoelectricity of PFs is described. At the end of this review, potential approaches to further improve the piezoelectricity of PFs are proposed.

Achieving single domain relaxor-PT crystals by high temperature poling

Single domain relaxor-PT crystals are important from both fundamental and application viewpoints. Compared to domain engineered relaxor-PT crystals, however, single domain crystals are prone to cracking during poling. In this paper, based on the analysis of the cracking phenomenon in [001] poled tetragonal 0.25Pb(In0.5Nb0.5)O3–0.37Pb(Mg1/3Nb2/3)O3–0.38PbTiO3 (PIN–PMN–PT) crystals, the non-180° ferroelastic domain switching was thought to be the dominant factor for cracking during the poling process. A high temperature poling technique, by which the domain switching can be greatly avoided, was proposed to achieve the single domain relaxor-PT crystals. By this poling approach, a quasi-single domain crystal was obtained without cracks. In addition, compared to room temperature poling, the high temperature poled PIN–PMN–PT crystals showed improved electromechanical properties, i.e., a low dielectric loss, a low strain–electric field hysteresis and a high mechanical quality factor, demonstrating a beneficial poling approach.

An efficient way to enhance output strain for shear mode Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals: Applying uniaxial stress perpendicular to polar direction

The shear piezoelectric behavior of [001] poled tetragonal and [011] poled rhombohedral Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) crystals, with “1T” and “2R” domain configurations, respectively, were investigated under uniaxial stress perpendicular to polar direction. The shear piezoelectric coefficient d15 was found to decrease with increasing compressive stress for both “1T” and “2R” crystals. Based on thermodynamic analysis, the phase structure can be stabilized by applying compressive stress perpendicular to polar direction, resulting in a “harder” polarization rotation process, accounts for the reduced shear piezoelectric coefficient. Of particular importance is that the allowable drive electric field was greatly increased and transverse dielectric loss was drastically reduced under compressive stress, leading to the improved maximum-shear-strain.

Pyroelectric properties of rhombohedral and tetragonal Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 crystals

Pyroelectric properties of rhombohedral and tetragonal single crystals Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 (PIN-PMN-PT) were investigated, with temperature from −100 °C to 100 °C. At room temperature, the pyroelectric coefficient p and the figure of merit Fd of rhombohedral crystals are 7.81 × 10−4 C/m2 K and 10.9 × 10−5 Pa−1/2, respectively, and 6.84 × 10−4 C/m2 K and 11.67 × 10−5 Pa−1/2, respectively, for tetragonal crystals. Although the coefficient p and Fd at room temperature are similar for rhombohedral and tetragonal crystals, the Fd of tetragonal crystal is much more stable with respect to temperature, owing to its higher phase transition temperature and stable mono-domain state. From room temperature to 100 °C, the Fd of rhombohedral crystal decreases from 10.74 × 10−5 Pa−1/2 to 5.3 × 10−5 Pa−1/2, while that of tetragonal crystals is nearly independent of temperature. Such investigation reveals that tetragonal PIN-PMN-PT crystal is more suitable for uncooled infrared detectors and imagers when c...

Growth, structure and electrical properties of mercury indium telluride single crystals

A new zinc-blende type photoelectronic single crystal, Hg(3−3x)In2xTe 3 (MIT), was grown by using the vertical Bridgman method. The structure of the MIT (x = 0.5) crystal was examined by x-ray powder diffraction. The lattice parameters were determined to be 6.2934 ± 0.0011 A with a defect zinc-blende structure, which belongs to the group F ¯ 43m. The melting point of the MIT crystal was measured by using the differential scanning calorimetry. Hall effect measurements on electrical properties at room temperature show that resistivity, carrier density and mobility of MIT crystal were 4.79 × 10 2 � cm, 2.83 × 10 13 cm −3 and 4.60 × 10 2 cm 2 V −1 s −1 , respectively. The electron effective mass at the bottom of the conduction band and the top of the valence band was calculated. It was found that the Fermi level of the MIT crystal was about 0.008 eV higher than that of the mid-gap. The experimental carrier concentration was in good accordance with the theoretical result.

Investigation on the Thermal Stability of Pb(Mg1/3Nb2/3)O3-PbTiO3 Single Crystals

Relaxor ferroelectric-based Pb(Mg1/3Nb2/3)O3–32PbTiO3 (PMN-32PT) single crystal was prepared by using the vertical Bridgman method at the optimized condition and the thermal stability with temperature under different conditions was analyzed through the differential scanning calorimetry (DSC) and the thermal gravity analysis (TGA). The phases were identified by XRD. DSC/TGA results of the as-grown PMN-32PT crystal indicated that PMN-32PT crystals was stability before melting in the sealed conditions while kept instability in the temperature higher than 900°C in the open system; the melting point of PMN-32PT was 1302.1°C in sealed condition while reduced to 1282.9°C in open system due to the evaporation of PbO and the transformation into pyrochlore phases.

High temperature x-ray diffraction study on phase transformation and lattice thermal expansion of mercury indium telluride crystals

The high temperature properties of Hg(3−3x)In2xTe3 (MIT) (x = 0.5) crystals grown by the vertical Bridgman method were investigated. The high temperature x-ray diffraction patterns between 25 and 300 °C indicated that an order–disorder phase transformation happens at ~290 °C. The mean thermal expansion coefficient of MIT crystal between 25 and 300 °C was calculated from the lattice parameter data to be 11.35 × 10−6 °C−1. The lattice parameters of MIT crystals were found to increase approximately linearly with temperature between 50 and 250 °C, but increased rather more rapidly between 250 and 300 °C and much more rapidly between 25 and 50 °C. The density of MIT crystal decreases from 6.248 g cm−3 at 25 °C to 6.189 g cm−3 at 300 °C with increasing temperature.

Growth, crystalline quality and transition variation of ternary Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 ferroelectric crystals

Bulk crystals of high Curie temperature (TC)24Pb(In1/2Nb1/2)O3–43Pb(Mg1/3Nb2/3)O3–33PbTiO3 (24PIN–43PMN–33PT) with 55 mm in diameter and 130 mm in length were reproducibly grown by the bottom-seeded Bridgman method. The X-ray diffraction (XRD) spectrum indicated that the as-grown crystal was a single phase with rhombohedral structure at room temperature, the domain morphology and the phase transition sequence of R → T →C were observed, the full width at half maximum (FWHM) of X-ray rocking curve of (002) face was about 0.77°, and the defect density was inferred to 2.56 × 1010cm-2. The measured density of the as-grown crystals was very close to the theoretical one. Variation of the transition temperature of the as-grown crystals along the growth direction revealed that TC increased linearly along the growth direction and rhombohedral to tetrahedral phase transition temperature (TRT) gradually decreased in the middle part of the ingot.

Variation of di-/piezoelectric properties of PIN-PMN-PT crystals near morphotropic phase boundary along the growth direction

25Pb(In<inf>1/2</inf>Nb<inf>1/2</inf>)O<inf>3</inf>-45Pb(Mg<inf>1/3</inf>Nb<inf>2/3</inf>)O<inf>3</inf> -30PbTiO<inf>3</inf> (PIN-PMN-PT) ingots with the dimensions of Ø55×130mm were successfully grown by vertical Bridgman technique. The as-grown PIN-PMN-PT crystals were oriented and characterized on (001) cuts. Variation of di-/piezoelectric properties of the as-grown PIN-PMN-PT crystals near morphotropic phase boundary (MPB) along the growth direction were investigated. Temperature dependence of dielectric permittivity advised 60∼135°C of rhombohedral to tetragonal phase transition temperature (T<inf>rt</inf>) and 120∼210°C of Curie temperature (T<inf>c</inf>) near MPB along the growth direction. PIN-PMN-PT crystals have coercive fields (E<inf>c</inf>) of about 4.35kV/cm, more than twice that of Pb(Mg<inf>1/3</inf>Nb<inf>2/3</inf>)O<inf>3</inf>-32PbTiO<inf>3</inf> (PMN-PT) and about 1% electric field strain. T<inf>c</inf> was found to increase linearly along the growth direction and T<inf>rt</inf> gradually decreased in the middle part of the ingot. The piezoelectric constant, d<inf>33</inf>, increased initially then kept around 2000pC/N at lower but near MPB and the dielectric constant, ε<inf>r</inf>, had the same trend with d<inf>33</inf> falling into the scope of 5000–6300.