Jinrong Cheng

Structural and dielectric properties of Ga-modified BiFeO3-PbTiO3 crystalline solutions

The dielectric and structural properties of Bi(GaxFe1−x)O3–PbTiO3 (BGF–PT) crystalline solutions have been investigated. Studies have focused on phase-pure perovskite materials. With increasing Ga content, we have found: (i) a coexistence of tetragonal and rhombohedral ferroelectric phases; (ii) a multicell perovskite structure for BGF–0.3PT; and (iii) a maximum tetragonal c/a ratio for the composition BGF–0.6PT with x=0.25. Also, Ga modification increases the electrical resistivity to ⩾1012u2009Ωu200acm, reduces the dielectric loss or tanu200aδ over a wide temperature range, and increases the dielectric constant K. We have developed BGF–PT materials with values of K>400 and of tanu200aδ<0.03.

Effects of La substituent on ferroelectric rhombohedral/tetragonal morphotropic phase boundary in (1−x)(Bi,La)(Ga0.05Fe0.95)O3–xPbTiO3 piezoelectric ceramics

Crystalline solutions of (1−x)(Bi,La)(Fe0.95Ga0.05)O3–xPbTiO3 (BLGF–PT) have been fabricated with La concentrations of 0, 10, and 20 at.u200a%. The BLGF–PT system has been found to have excellent insulation resistivity ⩽1013u2009Ωu200acm. In addition, La substituent was found to decrease the coercive field, resulting in much improved dielectric and piezoelectric properties. A shift in the morphotropic phase boundary of BLGF–PT with increasing La content was identified for x=0.3, 0.4, and 0.43. We have achieved optimized dielectric constant, loss factor, Curie temperature, remnant polarization, and piezoelectric d33 properties of 881, 0.037, 386u200a°C, 30u2009μC/cm2 and 163 pC/N, respectively, for 0.6BLGF–0.4PT with 10 at.u200a% La. These results clearly demonstrate that BLGF–PT is a competitive alternative piezoelectric material to Pb(Zr,Ti)O3 with reduced lead content.

Fabrication and characterization of xBiGaO3–(1−x)PbTiO3: a high temperature reduced Pb-content piezoelectric ceramic

Abstract Bismuth gallium based crystalline solutions, x BiGaO 3 –(1− x )PbTiO 3 (BG–PT), were studied as novel material group of low lead content perovskite ceramics. X-ray diffraction (XRD) was utilized to investigate the crystal structure and phase evolution. A pure perovskite phase with tetragonal symmetry was obtained for x ≤0.25. Differential scanning calorimetry (DSC) revealed that a first order solid-to-solid transformation occurs at 495 °C for x =0.2. The dielectric properties were investigated at room and elevated temperatures. Our results show that BG–PT is a good candidate high-temperature piezoelectric ceramic, with reduced lead content.

Structural and electrical properties of (1−x)Bi(Ga1/4Sc3/4)O3–xPbTiO3 piezoelectric ceramics

Bismuth containing crystalline solutions (1−x)Bi(Ga1/4Sc3/4)O3–xPbTiO3 (BGS–PT) have been developed using conventional ceramic technology. X-ray diffraction analysis reveals that BGS-PT has a perovskite structure, in which tetragonal to rhombohedral phase transformation appears for x=0.6. The dielectric properties were investigated at room and elevated temperatures, respectively, for different PT contents. BGS–PT for x=0.6 shows enhancement in dielectric constant K and piezoelectric constant d33 of 1180 and 124 pC/N, respectively, for the compositions investigated. The Curie temperature (Tc) of BGS–PT is in the range of 465–510u200a°C at least 100u200a°C higher than that of conventional Pb(Zr,Ti)O3 piezoelectric ceramics. The coercive field (Ec) of BGS–PT strongly depends on the PT content and can reach 75 kV/cm for x=0.8. Our results show that BGS–PT is a good low-lead high-temperature piezoelectric ceramic.

Electrical properties of sol-gel-derived Pb(Zr0.52Ti0.48)O3 thin films on a PbTiO3-coated stainless steel substrate

Lead zirconate titanate (PZT) thin films were deposited on stainless steel (SS) substrates by a sol-gel spin-on technique, and crystallized by a low-temperature annealing process. A lead titanate thin coating was deposited between the PZT film and SS substrate in order to decrease the annealing temperature. X-ray diffraction revealed that amorphous PZT thin layers crystallized into a perovskite phase on annealed at 550u200a°C for 0.5 h. No second phase formation, due to chemical reactions with the substrate, was observed. For films with a thickness of 1.68 μm, the dielectric constant, tanu200aδ, remnant polarization and coercive field were determined to be 280, 0.07, 35 μC/cm2, and 99 kV/cm, respectively. The transverse piezoelectric constant d31 was measured using a wafer flexural technique.

Dielectric properties of (100) textured thick Pb(ZrxTi1−x)O3 films with different Zr/Ti atom ratios

Near 4-μm-thick Pb(ZrxTi1−x)O3 (PZT) films with Zr/Ti ratios of 60/40, 52/48, and 45/55 were coated onto platinized silicon substrates by using 2-methoxyethanol based sol-gel spin-on techniques with a special thermal treatment process. The scanning electron microscopy observations show the columnar growth of grains. The analysis of x-ray diffraction data indicates that all PZT films exhibit (100) texture. The dielectric constants and dissipation factors of the films were measured at elevated temperatures and frequencies. It is found that Curie points of 60/40, 52/48, and 45/55 films are at 350, 375, and 422u200a°C, respectively. All these films exhibit high dielectric constants and remnant polarizations. A permittivity of 1658 and remnant polarization of 35 μC/cm2 had been achieved for the 60/40 films. No enhancement of the dielectric constant was observed in films with a Zr/Ti ratio close to morphotropic phase boundary. The high dielectric constant observed in films with the higher Zr content was explained b...

Self-poling Effects in Sol-gel Derived Pb(Zr 1-x Ti x )O 3 Thin Films

Based on the direct piezoelectric effect, the measurement of piezoelectric module d 33 was conducted to examine the self-poling effect in sol-gel derived Pb(Zr 1-x Ti x )O 3 (PZT) thin films. It is observed that as-prepared PZT thin films have piezoelectric responses being dependent upon the film thickness and composition. The higher d 33 of 26 pC/N is achieved for ∼0.4 μm thick PZT thin films with Zr/Ti ratio of 53/47. The d 33 value decreases with increasing the film thickness for as-prepared PZT thin films, however, increases for the same film after external poling. The origin of the self-poling effect was briefly discussed based on the formation of an internal bias field in PZT thin films.

High Temperature Dielectric Properties of Sol-Gel Derived Thick PZT thin Films with Different Zr/Ti Atom Ratios

PZT thin films of different thicknesses and Zr/Ti ratios of 60/40, 52/48 and 45/55 were coated onto platinized silicon substrates by using 2 methoxyethanol (2-MOE) based sol-gel spinon technique and crystallized with a rapid thermal annealing (RTA) process. XRD analysis revealed that thin PZT films exhibit random texture, while the thicker ones exhibit (100) texture, which was independent of composition. Dielectric constants and dissipation factors of PZT thin films were measured at elevated temperatures and as a function of frequency. For films with a thickness of ∼ 4 μm, the Curie points are at 350, 375 and 422°C for Zr/Ti ratios of 60/40, 52/48 and 45/55, respectively. All these films exhibit a high remnant polarization. A remnant polarization of 35 μC/cm 2 had been achieved for the 60/40 films. No enhancement of the dielectric constant was observed in films with a composition close to MPB. The higher dielectric constant observed in films with the highest Zr content was explained by the concept of domain engineering.