J. Zeng

Effect of low-melting additives on the structure, phase transitions, and dielectric properties of 0.36BiScO3 · 0.64PbTiO3 ceramics

Ceramic samples of 0.36BiScO3 · 0.64PbTiO3 morphotropic phase boundary solid solutions modified with low-melting additives (bismuth, nickel, and manganese oxides and lithium fluoride; < 5 wt %) have been prepared by solid-state reactions, and the phase formation, microstructure, and dielectric properties of the ceramics have been investigated. The additives were shown to lower the formation temperature of the solid solutions and raise the density of the ceramics. Varying the heat treatment conditions, we obtained single-phase samples, both large-grained, ranging in grain size from a few to tens of microns, and fine-grained, with a submicron-scale microstructure. The ceramics were shown to form through liquid-phase sintering. The additives influenced the dielectric properties, electrical conductivity, Curie temperature, and dielectric relaxation of the ceramics.

Phase transitions and the dielectric and piezoelectric properties of ceramic solid solutions based on BiScO3-PbTiO3

The ferroelectric and piezoelectric properties of ceramic solid solutions having a composition of (1−x)(Bi0.9Nd0.1)(Sc0.9B0.1)O3 − xPbTiO3 (x = 0.60–0.66; B = Lu, Yb, Er, Y) and obtained by solid state reaction were studied. An increase in the Curie temperature was found upon an increase in the concentration of lead titanate, while a drop occured upon the doping of the A and B sublattices. It was shown that at high temperatures, MnO2 and Bi2O3 additives lead to a reduction in the total conductivity and a dielectric loss of less than one order of magnitude. In modified ceramics, an increase in the d33 and kt piezoelectric coefficients was observed as well. The effects of dielectric relaxation that are determined by the composition of the ceramics were revealed.

Phase Transitions, Piezo- and Ferroelectric Properties of BiScO3-PbTiO3 Solid Solutions

Ceramic solid solutions (1-x)(Bi0.9Nd0.1)(Sc0.9B0.1)O3 - xPbTiO3 (x = 0.60–0.66; B - Lu, Yb, Er, Y) based on the compositions close to the morphotropic boundary, have been prepared. To improve the phase content and the resistance of ceramics, Bi2O3 and MnO2 additives were used. Phase composition, structure, microstructure, phase transitions, ferroelectric and piezoelectric properties have been studied. The 1st order ferroelectric phase transitions are marked by peaks near 700–750 K in dielectric permittivity and dielectric loss temperature dependences. Effect of dielectric relaxation was observed, its relation to composition of ceramics determined. The Curie temperature TC increase was observed with increasing the PbTiO3 constituent, while the TC decrease is typical of the A- or B-cations doped compositions. Introduction of MnO2 and/or Bi2O3 additives lead to the decrease of total conductivity and dielectric losses to more than one order at elevated temperatures. Enhanced d33 and kt values were measured in modified ceramics.

One step preparation of pure &#x1d749;-MnAl phase with high magnetization using strip casting method

Ferromagnetic phase of Mn-Al exhibits great potential in the rare-earth free permanent magnetic materials due to its high magnetocrystalline anisotropy, high magnetization, high Curie temperature and low cost. In this work, the strip casting technique was applied to prepare MnAl magnetic phase. X-ray diffraction and energy dispersive X-ray analyses indicate that the as-prepared Mn54Al46 strip sample consists of pure τ-MnAl magnetic phase. It is found that the composition of Mn54Al46 is suitable to prepare τ-MnAl phase during the strip casting process. The Mn54Al46 strip sample synthesized through the strip casting exhibits a fairly high magnetization of 114 emu/g under a field of 5 T, while the coercivity of iHc = 2.8 kOe, magnetization of M5T = 63.9 emu/g at room temperature can be obtained for Mn54Al46 powder sample. This preparation method can produce a large amount of τ-phase MnAl alloy and promote mass industrialized production.

Dielectric/ferroelectric and phase transition properties of PLZT ceramics

ABSTRACT The La doped ceramics PLZT-0.03/1-x/x (0.43 ≤ x ≤ 0.49) around morphotropic phase boundary (MPB) region were prepared by solid-state reaction. The ceramics exhibited diffused phase transition behavior, while MPB region showed the least degree of diffusion. It has been shown that distinct difference exists between poled and unpoled samples. All the samples exhibited thermal hysteresis behavior characteristic of the first order phase transition. The ferroelectric properties of the samples were also discussed.

Enhancement of Piezoelectric Properties of PMN-PT Ceramics at Low Temperatures

The temperature dependence of dielectric, elastic, electromechanical, and piezoelectric properties of (1-x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (PMN-xPT) ceramics near MPB with x = 0.33, 0.35, 0.36, 0.37, and 0.38 was systematically investigated within the temperature range 120–360 K. Compositions of x = 0.37 and 0.38 were found to exhibit temperature-independent piezoelectric properties over a temperature range from 185 to 360 K. The temperature-stable piezoelectric response was attributed to a counter-balance among the dielectric, elastic, and electromechanical responses in a broad ferroelectric phase transition that was revealed from the dielectric constant, elastic compliance constant, and electromechanical coupling factor.

Ferroelectric Phase Transitions in Aurivillius Structure Lead-Free CaBi4Ti4O15 and CaBi3.6Nd0.4Ti4O15 Ceramics

Ferroelectrics with high TC > 600 K attract much attention due to prospects of their applications at high temperatures. In this work, influence of partial substitutions on the crystal structure and dielectric properties of lead-free bismuth oxides Ca(Bi1-x Nd x )4Ti4O15 (x = 0, 0.1) have been studied. Ceramic solid solutions have been prepared by the solid state reactions. Optimal temperatures of synthesis and sintering of the samples were determined. Phase composition, structure and microstructure of the samples were studied using the X-ray diffraction and scanning electron microscopy methods, respectively. Phase transitions and ferroelectric properties were studied by the dielectric spectroscopy. Positive effect of the Mn2O3 and Bi2O3 additives was proved. They favor to improving density of ceramics, inhibiting grain growth and to decreasing dielectric loss.

The Piezoelectric Failure of the CeO2-Doped (Ca,Sr)Bi4Ti4O15 Ceramics at High Temperature

The CeO2-doped bismuth-layered structural (Ca,Sr)Bi4Ti4O15 ceramics, one of the most attractive materials with high Curie temperature were prepared by the solid state reaction method. The crystal structure of the ceramics was determined by X-ray diffraction. The doping of CeO2 increased the lattice parameters a, b, c and crystal volume, though the single orthorhombic structure phase was still remained. The effect on the content of the Ce ions to the dielectric properties of the ceramics were also investigated, such as the hysteresis loops, dielectric constants, Curie temperature (TC) and so on. The piezoelectric failure at the temperature much lower than the Curie temperature was found. The mechanism of the Ce ions doping and failure were also analyzed.

Microstructure and Electrical Properties of the PNN-PZT Thick Films Prepared by Electrophoretic Deposition

PNN-PZT thick films were prepared by electrophoretic deposition method on different substrates, such as Al2O3, PNN-PZT and Pt. The effects of the substrates and sintering temperature on the densification, microstructure, dielectric and ferroelectric properties of the PNN-PZT thick films were investigated. The results show that the density and the dielectric constant of the films deposited on the PNN-PZT ceramic substrates increase with the increasing of the sintering temperature. The polarization hysteresis loops reveal the ferroelectric property of the PNN-PZT thick films. The substrate is also very important for obtaining thick films with good properties. The high density PNN-PZT film deposited on the Pt foil was obtained with a dielectric constant of 1804 at 1 kHz and a remanent polarization of 20.8 μC/cm2.

Coercivity enhancement of sintered Nd-Fe-B magnets by chemical bath deposition

The chemical bath deposition (CBD) method is used to diffuse the heavy rare earth element in order to obtain the high coercivity magnets with low heavy rare earth element. The jet mill powders are soaked in the alcohol suspension of Dy(CH3CHOHCH3)3 (Dy-ipa) so that Nd2Fe14B powder particles are surrounded by Dy-ipa homogeneously. By adding 1.0 wt. % Dy, the coercivity of magnet is increased from 14.47 kOe to 17.55 kOe with slight reduction of remanence after grain boundary diffusion (GBD) in the sintering and annealing processes. The temperature coefficient of coercivity optimizes from -0.629 %/°C to -0.605 %/°C as well as that of remanence improves from -0.108 %/°C to -0.100 %/°C. The CBD method is helpful for thermal stability and alignment either. The relation between the microstructure and the coercivity has been studied systematically.