Excellent electrostrictive properties of low temperature sintered PZT ceramics with high concentration LiBiO2 sintering aid

The effect of LiBiO₂ (LBO) additive on the sintering of Pb_0.97La_0.03(Zr_0.53Ti_0.47)_0.9925O₃ (PLZT) ceramics was carefully investigated. 6.0 wt% LBO added PLZT powders could be fully densified to 98% relative density at a temperature as low as 950 °C. It is worthy to notice that there are distinct enhancements in piezoelectric and electrostrictive properties by increasing the soaking time from 2 h to 7 h, which could mainly originate from the improvement of crystallinity and grain size of PLZT ceramics. By controlling the soaking time and concentration of LBO addition, PLZT ceramics sintered at 950 °C could exhibit high curie temperature of 240 °C and very high S₁₁ of 0.22% under 3.0 kV/mm, which is even better than that of traditionally sintered PZT-5, PMN–PZT, and this is very promising for actuators designed in multilayer structure in high temperature environment.     

Characteristics of BaNd2Ti5O14 powders directly prepared by high-temperature spray pyrolysis

BaNd₂Ti₅O₁₄ powders were directly prepared by high-temperature spray pyrolysis. The powders prepared at temperatures of 1300 and 1500 °C exhibited a pure BaNd₂Ti₅O₁₄ phase. The powders prepared at 1300 °C were spherical in shape. However, the powders prepared at 1500 °C showed non-spherical shapes. The BaNd₂Ti₅O₁₄ powders had a composition similar to that of the spray solution. The mean sizes of the BaNd₂Ti₅O₁₄ powders increased from 0.23 to 0.60 μm when the concentration of the spray solution was increased from 0.01 to 0.2 M. At a sintering temperature of 1100 °C, bridge-like structures were formed between the powders. Pellets sintered at 1300 °C exhibited a dense structure comprising rod-like crystals.     

Phase,microstructure and ferroelectric properties of new complex-structured ferroelectric ceramics in the PZT–SBN system

This study aimed to fabricate and characterize new complex-structured ceramics with formula (1-x)Pb(Zr_0.52Ti_0.48)O₃–xSrBi₂Nb₂O₉ or (1-x)PZT–xSBN (where x=0, 0.1, 0.3 and 0.5 weight fraction). The ceramics were prepared by a solid-state mixed-oxide method and sintered at temperatures between 1000 and 1250 °C. Optimum sintering temperature for this system was found to be 1050 °C for 3 h dwell time. X-ray diffraction patterns of (1-x)PZT–xSBN powders showed peak intensities of two-phase mixture corresponding to the relative amount of each phase as a result of SBN addition. Microstructure of (1-x)PZT–xSBN ceramics showed a variation in grain shape and grain size. The small addition of SBN (x=0.1) was also found to improve ferroelectric properties of pure PZT ceramic.     

Dielectric and magnetic properties of BiFeO3 ceramics prepared by hydrothermal synthesis

Single-phase BiFeO₃ powders were prepared at a temperature of 200 °C by a hydrothermal synthesis. BiFeO₃ ceramics were prepared with the powders by a conventional ceramic process. The BiFeO₃ ceramics with no impurity phase were prepared at the sintering temperature of 650–800 °C. The dense microstructure was observed in the BiFeO₃ ceramics sintered at a temperature of 700 °C and higher. BiFeO₃ ceramics show linear M–H curves in low H, which are antiferromagnetic behaviors. The dielectric dispersion was observed at the frequency range of 10 kHz to 1 MHz in the BiFeO₃ ceramic sintered at 700 °C or lower. The dielectric constant and loss of the BiFeO₃ ceramics sintered at 750 °C or higher were about 85 and 0.4 at 100 kHz, respectively.     

LaCoO3 ceramics obtained from reactive powders

The aim of the present study was to establishing the correlation between the structure and properties of the LaCoO₃ powders obtained by aqueous sol–gel method with citric acid and their sintering behavior in order to obtain fully densified ceramics with perovskite structure. Two types of cobalt and lanthanum reagents were used in synthesis, namely nitrates and acetates. The sintering was realized at temperatures ranging between 800 and 1200 °C for 2 h. The sintered samples were investigated by classical ceramic methods (shrinkage, density, porosity) and by structural and morphological investigations: XRD, SEM, AFM and XPS. The electrical properties of the samples were determined by impedance spectroscopy. The ceramics obtained with powders starting with acetates have presented a lower sintering ability as compared with the samples obtained from powders starting with nitrates. LaCoO₃ ceramics with best properties was obtained from powders starting with nitrates sintered at 1100 °C.     

Low temperature sintering of PZT powders coated with Pb5Ge3O11 by sol–Gel method

Low temperature sintering of PZT powders was investigated using Pb₅Ge₃O₁₁(PGO) as a sintering aid. PZT powders with 150 nm particle size were coated with PGO which was prepared from precursor solutions of Ge(OiPr)₄ and Pb(NO₃)₂ by sol–gel method. 1 wt% PGO-added PZT powders were densified at 750°C for 2 h to sintered bodies with the relative density of approximately 95%. An addition of PGO improved the sinterability of PZT powders with a reduction of sintering temperature by about 300°C. Dielectric and piezoelectric properties of PGO-added PZT ceramics sintered at ≦950°C were superior to those without PGO additives. However, a higher sintering temperature above 1000°C deteriorated the dielectric and piezoelectric properties of PGO-added PZT ceramics. This may be attributed to the change of microstructure involving the formation of solid solution between PZT and PGO. The 1 wt% PGO-added PZT bodies sintered at 750°C exhibited an electromechanical coupling factor, Kp, of about 56%.     

Effect of calcination temperature on the fabrication of transparent lutetium titanate by spark plasma sintering

Transparent lutetium titanate (Lu₂Ti₂O₇) bodies were fabricated by spark plasma sintering using Lu₂O₃ and TiO₂ powders calcined from 700 °C to 1200 °C. No solid-state reaction was identified after calcination at 700 °C, whereas single-phase Lu₂Ti₂O₇ powder was prepared at 1100 and 1200 °C. The calcination at 700 °C promoted densification at the early stages of sintering, whereas residual pores at grain boundaries resulted in Lu₂Ti₂O₇ bodies with low transparency. Low-density and opaque Lu₂Ti₂O₇ bodies formed owing to the coarsening of the powder calcined at 1200 °C. The Lu₂Ti₂O₇ body sintered using the powder calcined at the moderate temperature of 1100 °C had a density of 99.5% with the highest transmittances of 41% and 74% at wavelengths of 550 nm and 2000 nm, respectively.     

Effect of Pb excess in sol–gel process on phase composition in PFN ceramics

Lead iron niobate Pb(Fe_0.5Nb_0.5)O₃ (PFN) precursors were prepared using sol–gel synthesis by mixing acetates Pb and Fe with Nb-ethylene glycol–tartarate (Pechini) complex at 80 °C and calcination of gels at 600 °C. Single pyrochlore phase with structure close to Pb₃Nb₄O₁₃ was formed in stoichiometric precursor and Pb₃Nb₄O₁₃ with small amount of perovskite phase Pb(Fe_0.5Nb_0.5)O₃ in nonstoichiometric precursor prepared with the excess of Pb in molar ratio (Pb:Fe:Nb = 1.2:0.5:0.5). Average particle sizes of PFN calcined powders were ～120 nm. The metastable pyrochlore phase was partially decomposed to perovskite phase at sintering temperature of 1150 °C for 2, 4 and 6 h. Excess of Pb caused increasing of the density (7.4 g/cm³) and content of the perovskite phase (～53 vol.%) in ceramics sintered for 4 h. In microstructures of PFN ceramics sintered at 1150 °C for different times, the bimodal grain size distribution was observed with small spherical grains of perovskite phase and larger octahedral grains, which represent the pyrochlore phase. Results of EDX analysis confirm that complex types of pyrochlore phases that differ in iron content were present in ceramics.     

Effects of Li2CO3 and Sm2O3 additives on low-temperature sintering and piezoelectric properties of PZN-PZT ceramics

To assist the development of applications for multilayer piezoelectric devices, the low-temperature sintering piezoelectric ceramics of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ with Li₂CO₃ and Sm₂O₃ additives were fabricated by a conventional solid-state reaction, and their structural and piezoelectric properties were studied. With the addition of Li₂CO₃, the minimum sintering temperature of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramics was reduced from 1125 °C to 950 °C through the formation of a liquid phase and its piezoelectric properties showed almost no degradation. When the sintering temperature was below 950 °C, however, the piezoelectric properties degraded obviously. The additional Sm₂O₃ resulted in a significant improvement in the piezoelectric properties of 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ ceramic with added Li₂CO₃. When sintered at 900 °C, the optimized properties of the 0.3Pb(Zn_1/3Nb_2/3)O₃-0.7Pb(Zr_0.49Ti_0.51)O₃ piezoelectric ceramic with 0.3 wt% Li₂CO₃ and 0.3 wt% Sm₂O₃ were obtained as d₃₃ = 483 pC/N, k₃₁ = 0.376, Q_m = 73, ɛ_r = 2524, tan δ = 0.0178.     

Microwave assisted synthesis of Dy2Ti2O7 ultrafine powders by sol–gel method

Dy₂Ti₂O₇ ultrafine powders ranging from 100 to 300 nm were successfully synthesized by sol–gel method. Particularly, the dried gel precursor was treated at different temperatures (700–1000 °C) via microwave-heating, which contributed to decreasing the grain size and reaction time. The phase composition and structural evolution of the final products were examined by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Furthermore, the resultant powders were selected to fabricate ceramics and rubber based absobers. Their sinterability, mechanical properties and neutron absorption ability were also studied. Results showed that the highest flexural strength of 99.0 MPa were obtained for Dy₂Ti₂O₇ samples when sintered at 1600 °C for 2 h in air atmosphere. Meanwhile, the neutron absorption rate of Dy₂Ti₂O₇ ceramics and rubber based absorbers could reach 97.39% and 80.00% respectively when the thickness of samples was set as 5.0 mm.     

Ni4Nb2O9 ceramics prepared by the reaction-sintering process

Fabrication of Ni₄Nb₂O₉ ceramics via a reaction-sintering process was investigated. A mixture of raw materials was sintered into ceramics by bypassing calcination and subsequent pulverization stages. Ni₄Nb₂O₉ phase appeared at 1300 °C and increased with increasing soak time. Ni₄Nb₂O₉ content was found >96% in 1350 °C/2 h sintering pellets. A density of 5.71 g/cm³ was obtained for pellets sintered at 1350 °C for 2 h. This reaches 96.5% of the theoretical density. As the sintering temperature increased to 1350 °C, an abnormal grain growth occurred and grains >100 μm could be found. ?_r of 15.4–16.9 are found in pellets sintered at 1200–1300 °C. Q × f increased from 9380 GHz in pellets sintered at 1200 °C to 14,650 GHz in pellets sintered at 1250 °C.     

Structure and electrical properties of PZT–PMS–PZN piezoelectric ceramics

The quaternary piezoelectric ceramics of Pb(Zr_0.52Ti_0.48)O₃–Pb(Mn_1/3Sb_2/3)O₃–Pb(Zn_1/3Nb_2/3)O₃ (PZT–PMS–PZN) with different PZN contents were synthesized by molten salt synthesis (MSS). The influence of PZN content on phase structure, microstructure, dielectric and piezoelectric properties was investigated in detail. The results of X-ray diffraction (XRD) show that the phase structure of ceramics transforms from rhombohedral phase to tetragonal phase with the increasing of PZN content. The morphotropic phase boundary (MPB) of composition is located in the range of PZN content from 2 to 7 mol%. The grain size of the ceramics gradually decreases with the increasing of PZN content. Dielectric and piezoelectric properties of ceramics are significantly influenced by the PZN content. Ceramics sintered at 1150 °C with 5 mol% PZN achieve excellent properties, which are as follows: Q_m = 1381, K_p = 0.64, d₃₃ = 369pC/N, tan δ = 0.0044 and T_c = 275 °C. The PZT–PMS–PZN system is a promising material for high power piezoelectric transformers application.     

Synthesis,sintering and characterization of PLZST perovskite prepared by a lactate precursor route

A lactate precursor route for synthesis of lanthanum-doped lead zirconate titanate stannate (PLZST) ceramic powders was developed, based on an aqueous solution of lactic acid and Pb²⁺, La³⁺, Zr⁴⁺, Ti⁴⁺, Sn⁴⁺ ions. The metal ions were brought in solution through complex formation with lactic acid. An amorphous precursor was prepared by dehydration of the soluble metal–ion–lactate complex solution. Heat treatment of the precursor at 650 °C for 2 h resulted in single phase perovskite PLZST powders. The effects of the ratio of lactic acid to mixed metal ions on the characteristics of PLZST powders were studied. The results showed that the powders prepared with the higher ratio (6:1) precursor consisted of finer particles with diameter of 45 nm and sintered readily to dense ceramics at the relatively low temperature of 1100 °C for 2 h. A typical antiferroelectric double polarization hysteresis loop was measured.     

Low temperature sintering of the Ba2Ti9O20 ceramics using B2O3/CuO and BaCu(B2O5) additives

The effects of B₂O₃/CuO and BaCu(B₂O₅) additives on the sintering temperature and microwave dielectric properties of Ba₂Ti₉O₂₀ ceramics were investigated. The B₂O₃ added Ba₂Ti₉O₂₀ ceramics were not able to be sintered below 1000 °C. However, when both CuO and B₂O₃ were added, they were sintered below 900 °C and had the good microwave dielectric properties. It was suggested that a liquid phase with the composition of BaCu(B₂O₅) was formed during the sintering and assisted the densification of the Ba₂Ti₉O₂₀ ceramics at low temperature. BaCu(B₂O₅) powders were produced and used to reduce the sintering temperature of the Ba₂Ti₉O₂₀ ceramics. Good microwave dielectric properties of Qxf = 16,000 GHz, ɛ_r = 36.0 and τ_f = 9.11 ppm/°C were obtained for the Ba₂Ti₉O₂₀ ceramics containing 10.0 mol% BaCu(B₂O₅) sintered at 875 °C for 2 h.     

Microstructure and electrical properties of ZnO–Bi2O3-based varistor ceramics by different sintering processes

The effect of sintering processes, such as open sintering, sintering inside a closed crucible, and sintering within a powder bed, on the microstructure and V–I characteristics of ZnO–Bi₂O₃-based varistor ceramics was investigated at sintering temperatures in the range 1000–1200 °C. The results from the experiments showed that the microstructure and electrical properties of the samples varied according to the sintering method and temperature. Optimal values for the electrical characteristics of the varistor ceramics by different sintering processes were obtained when the sintering was conducted at 1100 °C. At the same sintering temperature, the different processes affected the properties differently. At 1000 °C, the samples sintered within a powdered bed showed better electrical properties than those subjected to the other two processes, while at 1100 or 1200 °C, the samples sintered in an open crucible exhibited the best electrical properties.     

Nanoindentation study of nickel manganite ceramics obtained by a complex polymerization method

The chemical synthesis of nickel manganite powder was performed by a complex polymerization method (CPM). The obtained fine nanoscaled powders were uniaxially pressed and sintered at different temperatures: 1000–1200 °C for 2 h, and different atmospheres: air and oxygen. The highest density was obtained for the sample sintered at 1200 °C in oxygen atmosphere. The energy for direct band gap transition (Eg) calculated from the Tauc plot decreases from 1.51 to 1.40 eV with the increase of the sintering temperature. Indentation experiments were carried out using a three-sided pyramidal (Berkovich) diamond tip, and Young's modulus of elasticity and hardness of NTC (negative temperature coefficient) ceramics at various indentation depths were calculated. The highest hardness (0.754 GPa) and elastic modulus (16.888 GPa) are exhibited by the ceramics sintered at highest temperature in oxygen atmosphere.     

Densification and ablation behavior of ZrB2 ceramic with SiC and/or Fe additives fabricated at 1600 and 1800 °C

The effects of Fe and SiC additions on the densification, microstructure, and ablation properties of ZrB₂-based ceramics were investigated in this study. The sample powders were conventionally mixed by cemented carbide ball then sintered by spark plasma sintering. The ablation rates and behavior of the ceramics were investigated under an oxyacetylene torch environment at about 3000 °C. A sample with high relative density (96.3%), high flexural strength (415.6 MPa), and low linear ablation rate (−0.4 µm/s) was obtained via SPS at 1600 °C. Adding 4 vol% Fe was more beneficial to the density of ZrB₂ sintered at 1600 °C as compared to ZrB₂ sintered at 1800 °C. The ablation behavior and rates were similar among samples sintered at 1600 °C and 1800 °C.     

Microwave dielectric properties of Ba2Ti9O20 materials prepared by reaction sintering process

We synthesized the Ba₂Ti₉O₂₀ materials by direct reacting the nano-sized BaTiO₃ with TiO₂ powders. Pure Holland-like structure was obtained when the mixture of the nano-powders were calcined at 1100 °C. The influence of the processing method on the characteristics of the Ba₂Ti₉O₂₀ powders and the related microwave dielectric properties for the sintered Ba₂Ti₉O₂₀ materials was investigated. The combined high-energy-milling and ball-milling (HeM/BM) process results in pronounced improvement for the sinterability of the Ba₂Ti₉O₂₀ powders such that the samples attain a density higher than 96.2% T.D. when sintered at 1200 °C/4 h. Such a sintering temperature is significantly lower than the one needed for densifying the BM-processed samples to the same high density (1350 °C/4 h). However, the HeM/BM-processed samples show pronouncedly inferior microwave quality factor (Q × f-value) to the BM-processed ones. Raman spectroscopic and SEM microstructural analyses imply that the prime factor resulting in lower Q × f-value for HeM/BM-processed samples is the incomplete development of the granular structure.     

Transparent mullite ceramic from single-phase gel by Spark Plasma Sintering

Monophasic mullite precursors with composition of 3Al₂O₃·2SiO₂ (3:2) were synthesized and then were sintered by Spark Plasma Sintering (SPS) to form transparent mullite ceramics. The precursor powders were calcined at 1100 °C for 2 h. The sintering was carried out by heating the sample to 1450 °C, holding for 10 min. The sintered body obtained a relative bulk density of above 97.5% and an infrared transmittance of 75–82% in wavelength of 2.5–4.3 μm without any additive. When the precursor powders were calcined at below 1100 °C, it was unfavorable for completely eliminating the residual OH, H₂O and organic compound. However, when calcined temperature was too high, it was unfavorable either for full densification due to the absence of viscous flow of amorphous phase. At the same calcined temperature, the transmittance of sintered body was decreased with the increase of the sintering temperature above 1450 °C owing to the elongated grain growth.