Chengen Li

A-Site (MCe) Substitution Effects on the Structures and Properties of CaBi4Ti4O15 Ceramics

We investigated the effect of A-site compound substitution on the structures and properties of Ca0.8(MCe)0.1Bi4Ti4O15 (M denotes Li, Na and K) ceramics. The samples were prepared by the conventional ceramic technique. Sintering characteristics of Ca0.8(MCe)0.1Bi4Ti4O15 and CaBi4Ti4O15 ceramics were discussed. X-ray powder diffraction patterns of the three modified CBT-based compounds show a single phase of bismuth oxide layer type structure with m=4. The hysteresis loops of polarization versus electric field of the four compounds were also measured. A-site compound substitution improves the piezoelectric properties and the high-temperature resistivity of these materials. A-site (LiCe) and (KCe) substitution not only improves the Curie temperature but also decreases the temperature coefficient of dielectric constant (TKe). Among the three modified ceramics, only the Curie temperature of Ca0.8(NaCe)0.1Bi4Ti4O15 is lower than that of CaBi4Ti4O15; however, its TKe is the lowest. As a result, all the three modified CBT-based ceramics were found to be excellent high-temperature piezoelectric materials.

Effects of A-Site (NaCe) Substitution with Na-Deficiency on Structures and Properties of CaBi4Ti4O15-Based High-Curie-Temperature Ceramics

Three kinds of bismuth-layer-structured ferroelectric (BLSF) ceramics, CaBi4Ti4O15 (CBT), Ca0.8(CeNa)0.1Bi4Ti4O15 (CNBT), and Na-deficient Ca0.8(Ce0.1Na0.05\Box0.05)Bi4Ti4O15 [CN\BoxBT] (where \Box represents vacancies) were prepared by a conventional ceramic technique. X-ray powder diffraction showed that their crystal structures are a single phase of BLSF with m=4. Sintering characteristics of the three ceramics were also discussed. Scanning electron microscope (SEM) micrographs of CN\BoxBT showed that the grain is platelike. The A-site (NaCe) substitution can improve the piezoelectric constant d33 and high-temperature resistivity with decreasing Curie temperature. The modification by A-site (NaCe) substitution with Na-deficiency is more pronounced than CNBT, which not only leads to a very high piezoelectric constant d33 and high-temperature resistivity but also increases the Curie temperature. The reason for the high Tc (Tc=866°C) of CN\BoxBT is considered to be internal stress. As a result, Na-deficient CN\BoxBT ceramic is found to be an excellent high-temperature piezoelectric material.

Influence of sintering temperature on the properties of high Tc bismuth layer structure ceramics

Abstract Bismuth layer structure Ca 0.82 (NaCe) 0.09 Bi 4 Ti 4 O 15 piezoelectric ceramics were prepared by the conventional ceramic technique. Sintering characteristic of Ca 0.82 (NaCe) 0.09 Bi 4 Ti 4 O 15 was discussed. The X-ray powder diffraction pattern showed a single phase of bismuth oxide layer structure having general formula (Bi 2 O 2 ) 2+ (A m −1 B m O 3 m +1 ) 2− with m =4. Scanning electron microscope (SEM) micrographs of the natural surface of ceramic samples indicated that the anisotropy of growth of grains becomes stronger with the increase in the sintering temperature. With the increase in the sintering temperature, the resistivity and piezoelectric constant d 33 increased to a maximum value and then decreased, but the dielectric constant e 33 T / e 0 decreased. The Curie temperature and the capacitance temperature stability of the ceramics were improved with the increase in the density.

Formation of columbite-type precursors in the mixture of MgO-Fe2O3-Nb2O5 and the effects on fabrication of perovskites

Abstract All possible combinations of the three oxides, MgO, Fe 2 O 3 and Nb 2 O 5 have been investigated to trace the phase development during calcination by means of X-ray diffraction (XRD). It has been found that for the ternary system MgO–Fe 2 O 3 –Nb 2 O 5 , the phase evolvement in the process of calcining is not the simple superimposition of the three binary systems MgO–Fe 2 O 3 , MgO–Nb 2 O 5 and Fe 2 O 3 –Nb 2 O 5 . The reaction existing in the binary system MgO–Fe 2 O 3 no longer appears in the ternary system. Furthermore, Mg 4 Nb 2 O 9 , as a by-product of the binary system MgO–Nb 2 O 5 , does not form in the ternary system. Different precursors have different influence on the fabrication of perovskites. The possible mechanisms are discussed in detail.

Study on Low Frequency Internal Friction for Pb(Zr,Ti)O3 Ferroelectric Ceramics

The internal friction Q–1 and the square of vibration frequency f2 (proportional to shear modulus G) were measured as functions of temperature on undoped Pb(Zr0.7Ti0.3)O3 (PZT73) and Pb(Zr0.3Ti0.7)O3 (PZT37) ceramics from 20 to 500 °C. Experiments were performed on an inverted torsion pendulum at low frequencies (0.1 to 5 Hz). Two internal friction peaks were found in pure rhombohedral PZT73 ceramics. The high temperature peak PM, which appears near the Curie temperature, originates from the viscous movement of domain walls. The low temperature peak P1 is a broadened Debye peak in nature, and it is attributed to the oscillation damping of the domain walls presumably acted by charged oxygen vacancies. For the pure tetragonal PZT37 ceramics, another peak P2, which appears between P1 and PM, can be well described by the coupling model. It is thought to be caused by the relaxation of oxygen vacancy clusters near the 90° domains.

Effects of Processing Routes on Structures and Dielectric Properties of Lead Iron Niobate-Lead Magnesium Niobate Binary System

The binary system of lead magnesium niobate [Pb(Mg1/3Nb2/3)O3, PMN] and lead iron niobate [Pb(Fe1/2Nb1/2)O3, PFN] has been chosen to investigate the influence of different preparation routes on the microstructures and properties by means of X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), energy dispersion spectrometer (EDS) and dielectric measurements. It is found that for the binary system (1-x)PFN–xPMN, the change in Curie temperature is approximately linear with respect to PMN content in the range of x=0 to 0.5. With the increase in x, the Curie points shift to lower temperatures. Both calcining and sintering conditions have a non-negligible influence on the microstructure and the dielectric properties. The dielectric and other properties of samples prepared by single-step and two-step precalcination routes are compared and the possible mechanisms are discussed. Samples mixed-sintered at an appropriate temperature exhibit a different dielectric behavior, which is also discussed in detail in this paper.

Study of dielectric relaxation behavior and b-site ordering of Pb(Mg1/3Nb2/3)O3 (pmn)

Abstract Order-disorder of Pb(Mg1/3Nb2/3)O3 on B-site was studied through both the heat treatment and La+3 -doping methods. It is interpreted that enhance of degree of diffuse phase transition is of a formation of Mg+2/Nb+5 = 1 non-stoichiomatric short-range ordered micro-domains accompanied with segregation of Nb+5in disordered area. It is found that ordered degree, instead of size of ordered microdomain, could be intensified after annealing, however, size enlarged through La+3-doping.

The transport properties of Pr1.2Sr1.8Mn2O7 and Pr1Sr2Mn2O7 under pressure

This paper reports the electronic transport measurements of the single crystal Pr1.2Sr1.8Mn2O7 and Pr1Sr2Mn2O7 under pressure. The measurements in the ab plane for Pr1.2Sr1.8Mn2O7 show that the pressure induces a phase transition from a semiconducting state to a metallic state at 0.5 GPa, and then the transition temperature decreases rapidly with increasing pressure, indicating the pressure favors the paramagnetic semiconducting state and suppresses the ferromagnetic metallic state after the occurring of the transition. Moreover, for Pr1Sr2Mn2O7, the semiconducting-metallic state transition occurs at ambient pressure and the pressure favors the paramagnetic semiconducting state and suppresses the antiferromagnetic metallic state.

New high Tc piezoelectric ceramics with bismuth layer structure

Abstract The systematic investigation of the composition and structure of high Tc piezoelectric materials with bismuth layer structure was carried out. It was shown that a new kind of piezoelectric ceramics with the Curie temperature more than 850°C can be obtained by non-stoichiometric amount compound substitution of CaBi4Ti4O15-based (CBT-based) ceramics. The increase of the Curie temperature is due to the change of the phase transition energy caused by the structural distortion. The electrical properties and their high temperature stability of the modified CBT-based ceramics also were investigated from the point of view of its application as a high temperature piezoelectric material. The new material with a bismuth layer structure has the following properties: Tc>850°C, d33=18×l0−12C/N, ε33 T/ε0=130, TKC(500°C)<10×10−4/°C, pv(500°C)>2×107Ω.cm.

Study of phase conversion in PMN-PT ceramics near the morphotropic phase boundary

Abstract Phase compositions, grain sizes and domain widths of 0.65PMN-0.35PT ceramics sintered at various conditions have been investigated. It has been shown that a phase conversion from rhombohedral to tetragonal took place when the sintering temperatures were increased. This result is considered to be attributed to the increase of compressive stress in the grain, which makes the phase transition from tetragonal to rhombohedral difficult to occur, due to an expansion of cell volume. As a result, more tetragonal phases were left unchanged.