Microstructure and electrical properties of Er-doped 0.67 Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 ceramics with BaTiO3 templates

In this study, [001]-oriented Er-doped 0.67 Pb(Mg_1/3Nb_2/3)O₃-0.33PbTiO₃ (0.67PMN-0.33 PT) textured ceramics with different BaTiO₃ (BT) template concentrations were explored. The samples were prepared by tape-casting. Er³⁺ was added to modify the electrical properties of the polycrystalline ceramics, and the BT template was used to improve the texture of polycrystalline ceramics. The 0.67PMN-0.33 PT textured ceramics contained coexisting rhombohedral and tetragonal phases. The ceramics became increasingly textured as the sintering temperature increased up to 1250 °C. The piezoelectric coefficient of 0.67PMN-0.33 PT with 5 wt% BT was 634 pC/N, which is 1.2 times than that of randomly oriented 0.67PMN-0.33 PT. The strain of the ceramic with 5 wt% BT increased by 12.5% relative to a random control specimen. Analysis of the electrical properties and microstructure suggested that the enhancement of the piezoelectric coefficient and strain may be caused by the addition of Er³⁺ and the BT template. First, the directional growth of grains along the template affected the change-of-phase distribution of the system and formed a more adaptive phase. Second, Er³⁺ was substitutionally doped on the A-site of the perovskite to form local heterostructures. Finally, the relaxation components of the templates and Er³⁺ changed in the solid solution with the matrix. The solid solution of the BT templates and Er-doped-matrix powder changed the relaxation degree, which affected the interactions at the polar nanoregions and increased the piezoelectric coefficient of the ceramics.     

Double hysteresis loops and enhanced mechanical quality factor of Mn-doped 0.75PMN-0.25PT ceramics

Relaxor ferroelectric 0.75 Pb(Mg_1/3Nb_2/3)O₃-0.25PbTiO₃ (0.75PMN-0.25PT) ceramics with Mn-doping concentration of 0%, 1%, 2% and 3 mol% were prepared by two-step sintering. The phase composition, microstructure, dielectric property, ferroelectric property, piezoelectric property and electromechanical property were investigated. Results indicate that all ceramics exhibit pure perovskite phases and high density. Mn-doping induces some decrease in dielectric constant ε_r, dielectric loss tanδ, remnant polarization P_r, piezoelectric coefficient d₃₃, and electromechanical coupling coefficient k_p, while significant increase in mechanical quality factor Q_m and the figure of merit (FOM) of 0.75PMN-0.25PT ceramics. For 3 mol% Mn-doped 0.75PMN-0.25PT ceramics, Q_m enhances by 1449%, FOM increases by 923%, and tanδ decreases by 67%, which makes it more suitable for high power applications. Interestingly, double P-E loops are observed in 3 mol% Mn-doped 0.75PMN-0.25PT ceramics. The phenomenon was investigated by the symmetry-conforming principle of point defects and the internal bias field.     

Effects of annealing temperature on structure and electrical properties of sol–gel derived 0.65PMN-0.35PT thin film

0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (0.65PMN-0.35PT) thin films were deposited on Pt/Ti/SiO₂/Si substrates annealed from 550 to 700 °C using sol-gel process. The effects of annealing temperature on microstructure, insulating, ferroelectric and dielectric properties were characterized. The result reveals that 0.65PMN-0.35PT thin films possess a polycrystalline structure, matching well with the perovskite phase despite the existence of a slight pyrochlore phase. The film samples annealed at all temperatures exhibit relatively dense surfaces without any large voids and the grain size increases generally with the increase of the annealing temperature. Meanwhile, pyrochlore phase is considerably generated because of the deformation of perovskite phase caused by volatilization of Pb at an excessive high-temperature. The film annealed at 650 °C exhibits superior ferroelectricity with a remanent polarization (P_r) value of 13.31 μC/cm², dielectric constant (ε_r) of 1692 and relatively low dielectric loss (tanδ) of 0.122 at 10⁴ Hz due to the relatively homogeneous large grain size of 130 nm and low leakage current of approximately 10^-6 A/cm².     

Pyrochlore‐Free Ferroelectric 0.64Pb(Ni1/3Nb2/3)O3–0.36PbTiO3 Ceramics Synthesized by the Combustion Method

By adopting Nb₂O₅, HNO₃ and coordination agents EDTA as raw materials, pyrochlore‐free 0.64Pb(Ni_1/3Nb_2/3)O₃–0.36PbTiO₃(0.64PNN–0.36PT) powders were successfully synthesized via a combustion route. Free of pyrochlore phase was realized by the chelation formation of EDTA‐metal ions which isolate niobium and lead oxides and then prevent the formation of pyrochlore phases, therein generate the desired perovskite phases. Comparing the results with similar samples synthesized by the Columbite method, the new 0.64PNN–0.36PT ceramics here shown much better dielectric and ferroelectric performances: a maximum dielectric constant of 22 856 at 1 kHz and a remnant polarization of 21.6 μC/cm² at 40 kV/cm.     

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.     

Investigation of dielectric and piezoelectric properties in aliovalent Eu3+-modified Pb(Mg1/3Nb2/3)O3-PbTiO3 ceramics

Rare earth (Eu³⁺)-modified Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) polycrystalline ferroelectric ceramics were fabricated by high-temperature solid-state sintering, the phase structure, dielectric and piezoelectric properties were investigated. Eu³⁺ addition was found to significantly improve dielectric and piezoelectric properties of PMN-PT, where the optimized properties were achieved for the composition of 2.5 mol%Eu: 0.72PMN-0.28PT, with the piezoelectric d₃₃ = 1420 pC/N, dielectric ε_r = 12 200 and electromechanical k₃₃ = 0.78, respectively. All these results indicate that the Eu³⁺-doped PMN-PT ceramics are promising candidates for high-performance room-temperature piezoelectric devices.     

ZnO-activated formation of phase pure perovskite Pb(In1/2Nb1/2)O3-Pb(Zn1/3Nb2/3)O3-PbTiO3 powder

This paper reports on the phase formation of perovskite Pb(In_1/2Nb_1/2)O₃-Pb(Zn_1/3Nb_2/3)O₃-PbTiO₃ (PIN-PZN-PT) powder when doped with 0.04 to 0.83 mol% ZnO. Air calcination of undoped powder mixtures for 4 hours at 800°C resulted in a mixture of Pb₂Zn_0.29Nb_1.71O_6.565 pyrochlore, PIN-PZN-PT perovskite, and In₂O₃. ZnO dopant concentrations as low as 0.04 mol% increased the rate of perovskite formation and resulted in near phase pure perovskite powder of 0.5 μm particle size when heated at 800°C in air. In all cases PbTiO₃ and Pb(In_1/2Nb_1/2)O₃ formed prior to PIN-PZN-PT formation. ZnO doping promotes perovskite phase formation by increasing the reactivity of the intermediate pyrochlore phase by substituting Zn²⁺ on Nb⁵⁺ sites and forming oxygen vacancies when heated in air. Heating in high resulted in an incomplete reaction and a mixture of perovskite and pyrochlore whereas low resulted in phase separation into a mixture of rhombohedral perovskite, tetragonal perovskite, and pyrochlore. The sensitivity clearly shows that oxygen vacancies due to ZnO-doping are critical for synthesis of phase pure PIN-PZN-PT powder.     

Structure and enhanced properties of perovskite ferroelectric PNN–PZN–PMN–PZ–PT ceramics by Ni and Mg doping

Perovskite ferroelectric oxide ceramics of 0.1Pb(Ni_1/3Nb_2/3)O₃–0.35Pb(Zn_1/3Nb_2/3)O₃–0.15Pb(Mg_1/3Nb_2/3)O₃–0.1PbZrO₃–0.3PbTiO₃ (0.10PNN–0.35PZN–0.15PMN–0.10PZ–0.30PT) with excess MgO and NiO were investigated in this work. The effects of the excess MgO and NiO doping on the ceramic structure, density, dielectric, ferroelectric and piezoelectric properties were studied. The chemical states of nickel were examined using X-ray photoelectron spectroscopy (XPS). Both XPS experimental results and theoretical analyses on the basis of ionic packing indicated that the excess valence-two ions substituted the A-sites in the ABO₃ perovskite structure. By completely eliminating the pyrochlore phase and enhancing densification with the excess NiO and MgO, improved piezoelectric coefficient d₃₃ up to 459 pC/N, higher ferroelectric remnant polarization and dielectric constant were demonstrated when sintered at temperature as low as 850–950 °C.     

Effect of MgO and Y2O3 Doping on the Formation of Core–Shell Structure in BaTiO3 Ceramics

This study investigates the effects of doping BaTiO₃ with MgO and Y₂O₃ on the formation of core–shell structure. The MgO and Y₂O₃ enhanced the shrinkage upon sintering and inhibited the grain growth, respectively. However, increasing the amount of Y₂O₃ to 3.0 mol% suppressed the shrinkage upon sintering. The results of the diffusion experiment revealed that Y³⁺ was dissolved in the BaTiO₃ lattice to a depth of 5–10 nm inside the grains, whereas Mg²⁺ tended to remain close to the surfaces of the grains when sintered at 1150°C for 18 h, suggesting that Y³⁺ may have had a higher diffusion rate than Mg²⁺. The Mg²⁺ prevented the diffusion of Y³⁺ into the core during sintering. Therefore, Mg²⁺ plays an important role as a shell maker in the formation of the core–shell structure in the codoped system. The core–shell structure can be obtained in BaTiO₃ ceramics that are codoped with MgO and Y₂O₃ upon sintering at 1150°C for 3 h.     

A modified two-Stage mixed oxide synthetic route to lead magnesium niobate and lead iron niobate

A modified mixed oxide synthetic route has been developed for the synthesis of lead magnesium niobate [Pb(Mg_1/3Nb_2/3)O₃; PMN] and lead iron niobate [Pb(Fe_1/2Nb_1/2)O₃; PFN] powders. The formation of perovskite and pyrochlore phases in the calcined PMN and PFN powders has been investigated as a function of calcination temperature and time by XRD and DTA techniques. The particle size distribution of calcined powders was determined by laser diffraction, with the morphology, phase composition and crystal structure determined via SEM, TEM and EDX techniques. In both cases it has been found that cubic pyrochlore phases in the PbO–Nb₂O₅ system tend to form, as well as the perovskite phase. However, pyrochlore-free PMN and PFN powders were successfully obtained for a calcination temperature of 800°C for 4 and 3 h, respectively, without the introduction of excess PbO and/or MgO.     

Structural and electrical studies of excessively Sm2O3 substituted soft PZT nanoceramics

The solid solution of Pb_1-x Sm_2x/3 (Zr_0.6 Ti_0.4) O₃ ceramics with x = 0.1, 0.2, 0.3, and 0.4 was prepared via the high-energy ball milling technique. Further, the effect of excessive Sm₂O₃ substitution at Pb-site on structural, dielectric, and dc-conductivity properties was studied. The X-ray diffraction (XRD) analysis confirmed that all samples were crystallized with perovskite and pyrochlore diphase form. Excess Sm³⁺ substitution in the PZT system increases the pyrochlore volume fraction from 5 to 20% and induces a structural phase transition from rhombohedral to a tetragonal structure. The microstructural study by TEM and SEM indicated that the particles were spherical with an average size of 43–55 nm. The frequency and temperature-dependent dielectric constant for all compositions was carried out and it is obtained that the dielectric constant decreases with Sm³⁺ content. The phase transition temperature first decreases up to x = 0.2 and then increases for the higher concentration of samarium. The dc-conductivity studies revealed that all samples showed an unusual mixed TCR effect (both positive and negative temperature coefficient of resistance). Such properties of the studied samples indicate that the material is suitable for potential applications in thermistors, and temperature sensors of the automotive, and petroleum industries.     

Grain-orientation-engineered PMN-10PT ceramics for electrocaloric applications

The electrical properties of ferroelectric materials depend on their crystal orientations. The 〈001〉 and 〈111〉 textured 0.90Pb(Mg_1/3Nb_2/3)O₃–0.10PbTiO₃ (PMN-10PT) ceramics were synthesized using a template grain growth method and conventional solid sintering process. The Lotgering factors of the 〈001〉 and 〈111〉 textured PMN-10PT ceramics with 5% anisotropic BaTiO₃ (BT) precursors were 95% and 87%, respectively. The influence of grain orientation direction on dielectric properties was investigated, revealing that the permittivity of textured PMN-10PT ceramics (ε_r〈001〉 = 12200, ε_r〈111〉 = 11800) was lower than that of random ceramics (ε_r = 18700). Electrocaloric (EC) responses of the random and textured samples were analyzed using an indirect polarization-deduced method based on Maxwell's equations. When the applied field was 50 kV cm⁻¹, the 〈111〉 textured ceramics exhibited an enhanced adiabatic temperature change of 1.30 K, which was 20% higher than that of the random samples. In addition, the EC performance of the 〈111〉 oriented samples was significantly improved compared to that of the 〈001〉 oriented ones. This work characterizes the grain-orientation-dependent EC responses in the PMN-PT system, which would be a promising approach to EC response improvement in ferroelectric ceramics.     

Correlation of enhanced electrical properties and domain structure of high-TC PMN-PH-PT ceramics prepared by different methods

The dielectric, ferroelectric and piezoelectric properties of the high-Curie temperature (high-T_C) 0.15Pb(Mg_1/3Nb_2/3)O₃-0.38PbHfO₃-0.47PbTiO₃ (0.15PMN-0.38PH-0.47PT) ceramics synthesized by three different methods were investigated. The 0.15PMN-0.38PH-0.47PT ceramics prepared by the partial oxalate route present the best electrical properties (T_C =?291?°C, ε_m =?28,937, P_r =?32.89 μC/cm², E_c =?9.35?kV/cm, d₃₃ =?456.2 pC/N and K_p =?67.2%) and excellent thermal stability of the piezoactivity properties under T_C. Piezoresponse force microscopy (PFM) and confocal Raman microscopy (CRM) were employed to probe the nanoscale mechanism responsible for the performance difference of the 0.15PMN-0.38PH-0.47PT ceramics prepared by three different methods, disclosing the existence of the fine stripe domains, which make up the big island domains. The interplay between the macroscopic properties and nanoscopic domain structures of the 0.15PMN-0.38PH-0.47PT ceramics has been revealed. The better ferroelectric and piezoelectric response arise from the smaller domain size, which reduces the domain wall energy; whereas the higher coercive field E_c detected by the polarization-electric field (P-E) loops results from the harder domain switching for the 0.15PMN-0.38PH-0.47PT ceramics prepared by the wet chemical synthesis techniques.     

Achieving high piezoelectric performances with enhanced domain-wall contributions in <001>-textured Sm-modified PMN-29PT ceramics

1% Sm substituted PMN-29PT ([Sm_0.01Pb_0.985][(Mg_1/3Nb_2/3)_0.71Ti_0.29]O₃) textured ceramics with a Lotgering factor of up to 80 % were successfully prepared. The dielectric, ferroelectric and piezoelectric properties have been investigated in detail for both textured and non-textured ceramics. The heterogeneous templates are found to be critical for the change in relaxor behaviors, leading to the reduced T_f, T_m, ε_max and P_r in textured ceramics. The textured ceramics show an enhanced d₃₃ of 810 pC/N, about 1.6 times greater than their randomly oriented ceramic counterparts. The domain structures and their responses to applied electric fields have been studied using piezoresponse force microscopy, signifying the enhanced extrinsic contributions by the increased domain wall densities and dynamics. The improved dielectric and piezoelectric properties are discussed and explained from the view point of extrinsic contributions in textured ceramics. The results demonstrate that the textured Sm-PMN-PT piezoelectric ceramics could be promising high performance piezoelectrics with low cost.     

Templated grain growth of high coercive field CuO-doped textured PYN-PMN-PT ceramics

This paper explores the templated grain growth and texturing of Pb(Yb_1/2Nb_1/2)O₃-Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PYN-PMN-PT) ceramics. A PbO-CuO liquid phase was determined to substantially increase the growth of PYN-PMN-PT on barium titanate template particles. Texturing resulted in an 83% enhancement in strain behavior (754 pm/V) compared with random PYN-PMN-PT ceramics (413 pm/V). The increased Pb(Yb_1/2Nb_1/2)O₃ (PYN) content of textured 21PYN-41PMN-38PT resulted in a high coercive field of 13.9 kV/cm. Residual barium titanate templates reduced the polarization from 33.7 to 26.2 µC/cm² and slightly decreased the Curie temperature (236-224°C). These results show that textured PYN-PMN-PT is a promising material for high strain and coercive field transducers.     

Achieving both high electromechanical properties and temperature stability in textured PMN-PT ceramics

Textured piezoelectric ceramics, such as textured Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) ceramics, have attracted considerable attention from both academia and industry, as they possess crystal-like piezoelectric properties, high composition homogeneity, and low manufacturing cost. However, the main difficulty with the textured piezoelectric ceramics is the presence of BaTiO₃ (BT) templates, which greatly reduces their piezoelectricity and phase transition temperature. Thus, it is highly recommended to fabricate textured piezoelectric ceramics using as few templates as possible. Here, we successfully fabricated high-quality <001>-textured PMN-28PT ceramics (texturing degree of 99%) by using an extremely small amount of BT templates (1 vol.%) with the help of CuO/B₂O₃ sintering aids. The textured PMN-28PT ceramic exhibits 80% piezoelectric coefficient (d₃₃ ∼ 1200 pC/N), 96% electromechanical coefficient (k₃₃ ∼ 88%) and the same temperature stability (T_rt ∼ 100, T_c ∼ 150°C) when compared to its single crystal counterpart. In addition, by using an alternating current electric field poling (AC-poling), the piezoelectric coefficient d₃₃ and dielectric permittivity ε₃₃ of the textured PMN-28PT ceramics were further enhanced around 5–8%. It is believed that the advantages of high electromechanical properties, low cost, and easy mass production of textured PMN-28PT ceramic will make it a promising candidate for advanced electromechanical devices.     

Seeding effects on the mechanochemical synthesis of 0.9Pb(Mg1/3Nb2/3)O3–0.1PbTiO3

A systematic investigation of the seeding effects on the mechanochemical synthesis of lead magnesium niobate – lead titanate 0.9Pb(Mg_1/3Nb_2/3)O₃–0.1PbTiO₃ (PMN–10PT), one of the most studied relaxor-ferroelectric material for electrocaloric applications, is reported. The perovskite crystallisation process was followed by X-ray diffraction using the Rietveld refinement method and transmission electron microscopy. Compared to the mixed-oxides case which requires 143 h of high-energy milling, the milling time needed to obtain a phase-pure PMN–10PT perovskite using PT seeds is reduced almost twice. The presence of PT seeds leads to faster transitions from the amorphous to pyrochlore and to perovskite phases compared to the mixed-oxides case. A sintering study demonstrates, for the first time, that a second, metastable, pyrochlore phase is taking part in the processes of perovskite formation. The PMN–10PT ceramic prepared from the PT-seeded powder exhibits electrocaloric properties comparable to reported values for PMN–10 PT prepared from oxides.     

Heterovalent ions incorporated pyrochlore Sm2Zr2O7 ceramic for enhanced NO2 sensing

The present work demonstrated the heterovalent ions incorporated pyrochlore Sm₂Zr₂O₇ ceramic with high NO₂ sensitivity through molecular insights into the bond of [BO₆] unit and the sensing mechanism. An effective B-site strategy was developed to prepare a series of defective Sm2Zr1.95X0.05O7+δ (SZX, X= Mn²⁺, Ga³⁺, Sn⁴⁺, Nb⁵⁺, W⁶⁺) ceramics to create oxygen vacancies or interstitial oxygen induced which enhances the NO₂ sensing performances. The structural analyses carried out by XRD, SEM, XPS, Raman and the NO₂ adsorption on a cold surface of the sensor clarified the potential sensing mechanism. The electrochemical results clearly indicate that NO₂ sensing properties are closely related to the valence of doped cations. The sensor of Sm2Zr2O7 with Nb⁵⁺ arranged at B sites indicates high sensitivity, quick response/recovery speed, excellent selectivity and stability compared with others, exhibiting great application prospects for the automotive equipment.     

Thermodynamic properties of aluminum titanate-mullite composite ceramics containing heat stabilizer

Using Al₂O₃ and TiO₂ as raw materials, adding MgO as heat stabilizer and mullite as enhancer, aluminum titanate-mullite multiphase ceramics were successfully prepared by solid phase synthesis. The effects of MgO and mullite were systematically studied on the phase composition, microstructure, thermal stability, sintering properties, and mechanical properties of aluminum titanate ceramics. The results showed that the introduction of Mg²⁺ can partially replace Al³⁺ to form Mg_xAl_2(1-x)Ti_(1+x)O₅ solid solution, improved the thermal stability of aluminum titanate ceramics, and promoted the formation and growth of grains, which reduced the sintering temperature. The crack deflections caused by mullite particles improved the mechanical properties. The filling effect of mullite particles and the formation of silica in mullite raw materials were conducive to ceramic densification. The statistics of Mg4M10 sample were as follows: the porosity was only 2.9%, the flexural strength was as high as 64.15 MPa, and the thermal expansion coefficient was 1.35 × 10⁻⁶ K⁻¹ (RT-700°C), encouraging the application of ceramics with high thermal mechanical properties.     

Effects of W6+ substitution on crystal structure and microwave dielectric properties of Li3Mg2NbO6 ceramics

Li₃Mg₂(Nb_1-xW_x)O_6+x/2 (0 ≤ x ≤ 0.08) ceramics were synthesized by the solid-state reaction route. The effects of W⁶⁺ substitution on the phase composition, microstructure and microwave dielectric properties of Li₃Mg₂NbO₆ ceramics were investigated systematically. The XRD results showed that all the samples formed a pure solid solution in the whole doping range. The SEM iamges and relative density revealed the dense structure of Li₃Mg₂(Nb_1-xW_x)O_6+x/2 ceramics. The relationship between the crystal structure and dielectric properties of Li₃Mg₂(Nb_1-xW_x)O_6+x/2 ceramics was researched through polarizability, average bond valence, and bond energy. The substitution of W⁶⁺ for Nb⁵⁺ in Li₃Mg₂(Nb_1-xW_x)O_6+x/2 ceramics significantly promoted the Q × f values. In addition, the increase of W⁶⁺ content improved the thermal stability of the Li₃Mg₂(Nb_1-xW_x)O_6+x/2 ceramics. The Li₃Mg₂(Nb_0.94W_0.06)O_6.03 ceramics sintered at 1175 °C for 6h possessed excellent properties: ε_r ~ 15.82, Q × f ~ 124,187 GHz, τ_f ~ −18.28 ppm/°C.