Densification behavior and electrical properties of CuO-doped Pb(In1/2Nb1/2)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 ternary ceramics

CuO modified Pb(In_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PIN–PMN–PT) ternary relaxor based ferroelectrics with the composition near the morphotropic phase boundary were synthesized by two-step columbite precursor method. The introduction of CuO significantly improved the sinterability of PIN–PMN–PT ceramics, resulting in the full densification of samples at lower sintering temperatures. It also profoundly modified the crystal structure and fracture mode of the ceramics. Properly increasing CuO content led to the disappearance of rhombohedral-tetragonal phase transition, remarkably improved the Curie temperature (T_c), and made the ceramics more relaxorlike. The ternary ceramics doped with 0.25 wt% CuO possessed optimum piezoelectric properties (d₃₃=584 pC/N, d₃₃^*=948 pC/N, and k_p=0.68), high ferroelectric properties (E_c=9.9 kV/cm, and P_r=33.1 μC/cm²), low dielectric loss (tan δ=0.9%), and wider temperature usage range (T_c=225 °C). The obtained properties are much higher than those of previously reported PIN–PMN–PT based ceramics, indicating that CuO doped PIN–PMN–PT is a promising candidate for electromechanical applications with high performance and wide temperature/electric field usage ranges.     

Dielectric and piezoelectric properties of Pb(Sc1/2Nb1/2)O3–Pb(Ni1/3Nb2/3)O3–PbTiO3 ternary ceramic materials

The dielectric and electrical properties of xPb(Sc_1/2Nb_1/2)O₃–yPb(Ni_1/3Nb_2/3)O₃–zPbTiO₃ (PSNNT 100x/100y/100z) ternary ceramic materials near the morphotropic phase boundary (MPB) were investigated. The MPB follows on almost linear region between PSNNT 58/00/42 and PSNNT 00/68/32 of the binary systems. The maximum electromechanical coupling factor kp=70·7% was found at PSNNT 36/26/38, where ε₃₃^T/ε₀=3019 and Tc=210°C were obtained. These values are similar to those of the Pb(Sc_1/2Nb_1/2)O₃–Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ system and better than those of PZT.     

Low-temperature sintering of 12Pb(Ni1/3Sb2/3)O3–40PbZrO3–48PbTiO3 with V2O5 and excess PbO additives

Low-temperature sintering of 12Pb(Ni_1/3Sb_2/3)O₃–40PbZrO₃–48PbTiO₃ (12PNS–40PZ–48PT) calcined powders with V₂O₅ and excess PbO additives has been investigated. Adding 0.20 to 0.40 wt.% V₂O₅ and 1.0 wt.% excess PbO to 12PNS–40PZ–48PT calcined powders and sintering at 950 °C for 4 h, the sintered samples only contain the perovskite structure. The calcined powders are doped with 3.0 wt.% excess PbO and 0.20 to 1.0 wt.% V₂O₅ and sintered at 950 °C for 4 h, the coexistence of both tetragonal and rhombohedral phases with the minor phase of pyrochlore is observed. During the calcined powders contain 1.0 wt.% excess PbO and are sintered at 950 to 975 °C for 2 h, the bulk density decreases with V₂O₅ addition greater than 0.6 wt.%. When the calcined powders with 3.0 wt.% excess PbO are sintered at 900 to 975 °C for 2 h, the bulk density decreases with added V₂O₅ content increased. The values of the planar coupling coefficient (K_p) approach the maxima, namely, 0.51 obtained for the compacts containing 0.40 wt.% V₂O₅ and 1.0 wt.% excess PbO and sintered at 950 °C. As the calcined powders are added with 3.0 wt.% excess PbO and 0.80 wt.% V₂O₅ and sintered at 975 °C for 2 h, the maximum Q_m value 1100 is obtained.     

Domain structure and evolution in ZnO-modified Pb(Mg1/3Nb2/3)O3–0.32PbTiO3 ceramics

The doping of ZnO is efficient to improve the piezoelectric property and thermal stability of Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) based ceramics. However, the underlying physics, especially the local domain structures of the ZnO modified PMN–PT ceramics, which is strongly associated with the electric properties, is not clear yet. In this paper, we investigated the local domain structures and their evolution as a function of x in PMN–0.32PT:xZnO ceramics. It was found that, the domain evolution is mainly caused by the growth of grain size induced by the sintering aiding effect of ZnO at x < 0.04, and the domain evolution can be attributed to the phase transition induced by the partial replacement of Mg²⁺ by Zn²⁺ in the B-site of PMN–PT lattice at x > 0.06. Furthermore, we also investigated the domain structure evolution as functions of temperature and local external electric field in PMN–0.32PT:0.06ZnO ceramics, which exhibited superior piezoelectric property relative to other compositions. We found that the irregular nanodomains are more stable at high-temperature range, and the regular non-180° domains exhibited more complex rotation behavior under local electric field, which probably leads to the thermal stability and piezoelectric property enhancement in the ZnO-modified PMN–0.32PT ceramics.     

Investigations on electric properties and domain structures of Nd-doped 0.70Pb(Mg1/3Nb2/3)O3–0.30PbTiO3 relaxor ferroelectric ceramics with high piezoelectric properties

Although rare earth neodymium (Nd) doping is common in Pb(Mg1/3Nb2/3)O₃–PbTiO₃ (PMN–PT) single crystals, it is rarely reported in PMN–PT ceramics. To explore the effect of Nd doping on PMN–PT ceramics, PMN–30PT:xNd³⁺ (x = 0%, 1%, 2%, and 3%) relaxor ferroelectric ceramics were fabricated using a solid-state method via two-step sintering. An enhanced piezoelectric charge coefficient (d₃₃) of ∼870 pC/N and a high piezoelectric strain coefficient (d₃₃*) of ∼1025 pm/V were achieved for x = 2%. Through Rayleigh analysis of polarization–electric field (P–E) hysteresis loops under small electric fields, it was found that the dielectric property was mainly influenced by the intrinsic contribution (local lattice distortion). Furthermore, by investigating domain configurations, high piezoelectric properties were found to be associated with the domain size reduction and local structural heterogeneity. The results indicate that the PMN–30PT:xNd³⁺ ceramics is a promising material for electronic devices, and that rare earth Nd doping is an efficient strategy for improving the electronic performance of Pb-based relaxor ferroelectrics.     

A new Pb(Lu1/2Nb1/2)O3–PbZrO3–PbTiO3 ternary solid solution with morphotropic region and high Curie temperature

A ceramic ternary system of (1?x?y)Pb(Lu_1/2Nb_1/2)O₃–xPbZrO₃–yPbTiO₃ (PLuN–PZ–PT) has been prepared by two-step synthetic process and characterized by X-ray powder diffraction and electric measurements. A morphotropic phase boundary (MPB) region has been delimited in the ternary system at room temperature. With the PLuN content increasing, the morphotropic phase boundary region becomes broad as well as the dielectric peak. The best comprehensive piezoelectric properties were achieved at MPB composition 0.42PLuN–0.1PZ–0.48PT, with the piezoelectric coefficients d₃₃, the Curie temperature T_c, the planar electromechanical coupling factor K_p, and the remnant polarizations P_r being 367 pC/N, 360 °С, 68% and 35 μС/cm², respectively. The results indicate that the PLuN–PZ–PT ternary ferroelectric material may be a promising candidate for high-power electromechanical transducers that can operate in a large temperature range.     

Modified Pb(Mg1/3Nb2/3)O3-PbZrO3–PbTiO3 ceramics with high piezoelectricity and temperature stability

There is a great demand to develop ferroelectric ceramics with both high piezoelectric coefficient and broad temperature usage range for emerging electromechanical applications. Herein, a series of Sm³⁺-doped 0.25Pb(Mg_1/3Nb_2/3)O₃-(0.75−x)PbZrO₃-xPbTiO₃ ceramics were fabricated by solid-state reaction method. The phase structure, dielectric and piezoelectric properties were investigated, where the optimum piezoelectric coefficient d₃₃ = 745 pC/N and electromechanical coupling factor k₃₃ = 0.79 were obtained at the morphotropic phase boundary composition x = 0.39, with good Curie temperature T_C of 242°C. Of particular importance is that high-temperature stability of the piezoelectric and field-induced strain was obtained over the temperature range up to 230°C for the tetragonal compositions of x = 0.40. The underlying mechanism responsible for the high piezoelectricity and temperature stability is the synergistic contribution of the MPB and local structural heterogeneity, providing a good paradigm for the design of high-performance piezoelectric materials to meet the challenge of piezoelectric applications at elevated temperature.     

Effect of compositional modifications on microstructure development and dielectric properties of Pb(Mg1/3Nb2/3)O3–PbTiO3 solid solutions

The effect of minor additions of excess MgO and PbO on the sintering characteristics, microstructure development and dielectric properties of perovskite-based Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ solid solutions was investigated. Both MgO and PbO are compatible with the Pb(Mg_1/3Nb_2/3)O₃-based solid solutions and thus, these phases co-exist with one another during sintering at elevated temperatures. On sintering a solid solution composition Pb[(Mg_1/3Nb_2/3)_0.9Ti_0.1]O₃ with minor additions of MgO, the excess MgO remained as a discrete phase in the ceramics at temperatures up to 1230 °C and inhibited grain growth. Above this temperature, MgO combined with the solid solution to form a liquid phase, which caused an enhancement of the densification process. On sintering the solid solution with excess PbO, a low-temperature melting PbO-rich liquid phase was formed, which promoted the densification process with inhomogeneous grain growth. Simultaneous additions of 1.0 wt.% MgO and 2.0 wt.% PbO to the Pb[(Mg_1/3Nb_2/3)_0.9Ti_0.1]O₃ solid solution and sintering the resulting material at 1000 °C for 3 h led to the formation of a dense and homogeneous microstructure consisting of evenly distributed grains with an average grain size of 10 μm. The peak dielectric constant of this composition (at ≈38 °C), measured at a frequency of 1 kHz, was 18,000 with a dissipation factor of <2%.     

Effects of microstructure on the microwave dielectric properties of Ba(Co1/3Nb2/3)O3 and (1−x)Ba(Co1/3Nb2/3)O3–xBa(Zn1/3Nb2/3)O3 ceramics

Ba(Co_1/3Nb_2/3)O₃(BCN) has a 1:2 ordered hexagonal structure. A large amount of the liquid phase, which contains high concentrations of Ba and Nb ions was found in the BCN ceramics. Q-values of BCN increased with increasing sintering temperature; however, it significantly decreased when the sintering temperature exceeded 1400 °C. The presence of a large amount of liquid phase could be responsible for the decrease of the Q-value. For (1−x)Ba(Co_1/3Nb_2/3)O₃–xBa(Zn_1/3Nb_2/3)O₃ [(1−x)BCN–xBZN] ceramics, the 1:2 ordered hexagonal structure was observed in the specimens with x⩽0.3 and the BaNb₆O₁₆ second phase was found in the specimens with x⩾0.6. Grain growth, which is related to the BaNb₆O₁₆ second phase occurred in the specimens with x⩾0.5. In this work, the excellent microwave dielectric properties of τ_f=0.0 ppm/°C, ε_r=34.5 and Q×f=97,000 GHz were obtained for the 0.7BCN–0.3BZN ceramics sintered at 1400 °C for 20 h.     

Characterization and catalytic properties of MoO3–V2O5/Nb2O5 catalysts

The influence of molybdenum oxide on the dispersion of vanadium oxide supported on niobia was investigated. A series of MoO₃–V₂O₅/Nb₂O₅ catalysts with varying MoO₃ content ranging from 1% to 5% (w/w) with fixed V₂O₅ content were prepared by impregnation of previously prepared 5 wt% V₂O₅/Nb₂O₅ with requisite amounts of ammonium molybdate solution. X-ray diffraction patterns indicate the presence of β-(Nb,V)₂O₅ phase with the addition of MoO₃ up to a loading of 3 wt%. Temperature-programmed reduction (TPR) results suggest that the reducibility is decreasing with MoO₃ loading. The results of temperature programmed desorption (TPD) of ammonia suggest that the acidity of the catalysts increased with the addition of MoO₃. The catalytic properties of the catalysts in the ammoxidation of 3-picoline were correlated with the characterization data.     

Dielectric behaviors of Nb2O5–Co2O3 doped BaTiO3–Bi(Mg1/2Ti1/2)O3 ceramics

Nb₂O₅ and Nb–Co doped 0.85BaTiO₃–0.15Bi(Mg_1/2Ti_1/2)O₃ (0.85BT–0.15BMT) ceramics were investigated. From XRD patterns, undesired phase was observed when the (Nb₂O₅/Nb-Co) doping levels exceed 3 wt.%/2 wt.%, giving rise to the deteriorate dielectric constant. The 0.85BT–0.15BMT ceramics doped with 2 wt.%Nb₂O₅ was found to possess a moderate dielectric constant (? ～ 1000) and low dielectric loss (tan δ = 0.9%) at room temperature and 1 kHz, showing flat dielectric behavior over the temperature range from ?55 to 155 °C. It was found that the formation of core–shell structure in the BT based ceramics is controlled by the doping sequence of Nb- and Bi-oxides.     

Effect of adding Y2O3 on structural and mechanical properties of Al2O3–ZrO2 ceramics

The effects of adding 1–8 wt% Y₂O₃ on phase formation and fracture toughness of Al₂O₃–xZrO₂–Y₂O₃(AZY) ceramics were studied. Phase formations of the samples were characterized by the X-ray diffraction (XRD) technique. It was found that the major phase was rhombohedral-Al₂O₃, while the minor phase consisted of the monoclinic-ZrO₂, tetragonal-ZrO₂ and monoclinic-Y₂O₃. It was found that Y₂O₃ contents did not clearly influence grain shape of AZY ceramics. The results obtained from the microhardness test could be used to evaluate the fracture toughness. It was found that the smaller grains had high fracture toughness. The maximum fracture toughness of 4.827 MPa m^1/2 was obtained from 4 wt% Y₂O₃. Refinement of lattice parameters using Rietveld analysis revealed the quantitative phases of AZY ceramics. This shows that under adding Y₂O₃ conditions the proportion of tetragonal-ZrO₂ phase plays an important role for the mechanical properties of AZY ceramics.     

Effect of Ba(Zn1/3Nb2/3)O3 modification on structure and ferroelectric properties of 0.6Pb(Mg1/3Nb2/3)O3–0.4Pb(Zr0.52Ti0.48)O3 ceramics

In this study, (1−x)[0.6Pb(Mg_1/3Nb_2/3)O₃–0.4Pb(Zr_0.52Ti_0.48)O₃]–xBa(Zn_1/3Nb_2/3)O₃; (1−x)PMNZT60/40–xBZN having x=0, 2.5, 5, 7.5, and 10 mol% ceramics were prepared by mixed oxide powder method and sintered using a two-step process. Phase transitions were investigated by XRD, microstructure by SEM, crystal morphology by TEM, the dielectric and ferroelectric properties by capacitance measurement setup and modified Sawyer-Tower circuit, respectively. The dielectric constant and dielectric loss tangent were measured as functions of both temperature and frequency. The XRD results show the phase transition from tetragonal phase to pseudo-cubic phase with addition of BZN in PMNZT system. Grain size of about 1.23–2.42 μm and crystallite size in a range of 421–2152 nm were obtained. The pure-phase 0.6PMN–0.4PZT ceramics show the normal ferroelectric behavior. The 0.95(PMNZT60/40)–0.05BZN and 0.925(PMNZT60/40)–0.075BZN showed a broad and diffused dielectric properties and the dispersive phase transition, indicating the relaxor ferroelectric behavior. The transition temperature in the BZN-modified PMNZT system is seen to decrease from 166 °C in pure PMNZT60/40 to 102 °C and 54 °C with increasing BZN content to 5 and 10 mol%, respectively. In addition, the maximum dielectric constant is decreased with increasing BZN content. The P–E hysteresis loop measurements show the change from the normal ferroelectric behavior in PMNZT60/40 ceramic to more relaxor behavior that was induced with BZN addition. These results clearly demonstrated the significance of BZN to the electrical responses of the PMNZT60/40 system.     

Domain morphology evolution associated with the relaxor–normal ferroelectric transition in the Bi- and Zn-modified Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 system

To understand the dielectric behavior from a viewpoint of domain configuration, the domain morphology evolution in (Pb_0.985Bi_0.01)(Ni_1/4Zn_1/12Nb_2/3)_0.2(Zr_1-σTi_σ)_0.8O₃ ceramics (0.30⩽σ⩽0.60) has been investigated by transmission electron microscopy and high resolution electron microscopy. The results indicated that the domain morphology evolved from the normal micron-sized domains to herringbone domain patterns, and finally to the polar nanodoamains approximately 3∼6 nm in size when the PT content was decreased from 60 to 30 mol%. The normal twin-related 90° macrodomains are closely correlated with the normal dielectric response of the composition with higher PT content, whereas the relaxor response of the composition with lower PT content is directly attributable to nanometer domains that contain 1:1 short-range ordering on the B-site sub-lattice. A model is proposed to describe the effect of the PbTiO₃ content on the ferroelectric domain morphology evolution in the system.     

The characteristics of ZnO–Bi2O3-based varistor ceramics doped with Y2O3 and varying amounts of Sb2O3

ZnO–Bi₂O₃-based varistor samples doped with 0.45 mol% of Y₂O₃ and varying amounts of Sb₂O₃ in the range from 1.8 to 0.0 mol% were fired at 1230 °C. Only in the samples co-doped with Sb₂O₃ did doping with Y₂O₃ resulted in the formation of a fine-grained Bi–Zn–Sb–Y–O phase (the Y₂O₃-containing phase) at the grain boundaries, which very effectively hinders the grain growth. Despite of a decrease in the amount of added Sb₂O₃ from 1.8 to 0.45 mol% and a significant decrease in the amount of spinel phase the samples had a similar ZnO grain size and a threshold voltage of 200 V/mm. The results confirmed that doping with Y₂O₃ is a very promising route for the production of fine-grained high-voltage ZnO–Bi₂O₃-based varistor ceramics, and determining the proper amounts of added Sb₂O₃ and Y₂O₃ is of great importance.     

Piezoelectric properties of highly densified 0.01Pb (Mg1/2W1/2)O3–0.41Pb (Ni1/3Nb2/3)O3–0.35PbTiO3–0.23PbZrO3+0.1 wt% Y2O3+1.5 wt% ZnO thick films on alumina substrate

This paper reports on the formation of highly densified piezoelectric thick films of 0.01Pb(Mg_1/2W_1/2)O₃–0.41Pb(Ni_1/3Nb_2/3)O₃–0.35PbTiO₃–0.23PbZrO₃+0.1 wt% Y₂O₃+1.5 wt% ZnO (PMW–PNN–PT–PZ+YZ) on alumina substrate by the screen-printing method. To increase the packing density of powder in screen-printing paste, attrition milled nano-scale powder was mixed with ball milled micro-scale powder, while the particle size distribution was properly controlled. Furthermore, the cold isostatic pressing process was used to improve the green density of the piezoelectric thick films. As a result of these processes, the PMW–PNN–PT–PZ+YZ thick film, sintered at 890 °C for 2 h, showed enhanced piezoelectric properties such as P_r=42 μC/cm², E_c=25 kV/cm, and d₃₃=100 pC/N, in comparison with other reports. Such prominent piezoelectric properties of PMW–PNN–PT–PZ+YZ thick films using bi-modal particle distribution and the CIP process can be applied to functional thick films in MEMS applications such as micro actuators and sensors.     

Microwave dielectric properties of Bi2O3-doped Ca[(Li1/3Nb2/3)1−xTix]O3−δ ceramics

The effect of the additive on the densification, low temperature sintering, and microwave dielectric properties of the Ca[(Li_1/3Nb_2/3)_1−xTi_x]O_3−δ(CLNT) was investigated. Bi₂O₃ addition improved the densification and reduced the sintering temperature from 1150 to 900 °C of CLNT microwave dielectric ceramics. As the Bi₂O₃ content increased, the dielectric constant (ε_r) and bulk density increased. The quality factor (Q·f₀), however, was decreased slightly. The temperature coefficient of resonant frequency (τ_f) shifted to a positive value with increasing Bi₂O₃ content. The dielectric properties (ε_r, Q·f_0, τ_f) of Ca[(Li_1/3Nb_2/3)_0.95Ti_0.05]O_3−δ and Ca[(Li_1/3Nb_2/3)_0.8 Ti_0.2]O_3−δ with 5 wt.% Bi₂O₃ sintered at 900 °C for 3 were 20, 6500 GHz, −4 ppm/°C, and 35, 11,000 GHz, 13 ppm/°, respectively. The relationship between the microstructure and dielectric properties was studied by X-ray diffraction (XRD), and SEM.     

Preparation and properties of porous SiC–Al2O3 ceramics using coal ash

In this paper, we first reported that porous SiC–Al₂O₃ ceramics were prepared from solid waste coal ash, activated carbon, and commercial SiC powder by a carbothermal reduction reaction (CRR) method under Ar atmosphere. The effects of addition amounts of SiC (0, 10, 15, and 20 wt%) on the postsintering properties of as-prepared porous SiC–Al₂O₃ ceramics, such as phase composition, microstructure, apparent porosity, bulk density, pore size distribution, compressive strength, thermal shock resistance, and thermal diffusivity have been investigated. It was found that the final products are β-SiC and α-Al₂O₃. Meanwhile, the SEM shows the pores distribute uniformly and the body gradually contacts closely in the porous SiC–Al₂O₃ ceramics. The properties of as-prepared porous SiC–Al₂O₃ ceramics were found to be remarkably improved by adding proper amounts of SiC (10, 15, and 20 wt%). However, further increasing the amount of SiC leads to a decrease in thermal shock resistance and mechanical properties. Porous SiC–Al₂O₃ ceramics doped with 10 wt% SiC and sintered at 1600°C for 5 hours with the median pore diameter of 4.24 μm, room-temperature compressive strength of 21.70 MPa, apparent porosity of 48%, and thermal diffusivity of 0.0194 cm²/s were successfully obtained.