Effects of Nb doping on the microstructure,ferroelectric and piezoelectric properties of 0.7BiFeO<Subscript>3</Subscript>–0.3BaTiO<Subscript>3</Subscript> lead-free ceramics

Donor-doped lead-free Bi_0.7Ba_0.3(Fe_0.7Ti_0.3)_1?x Nb_0.66x O₃ + 1 mol% MnO₂ ceramics were prepared by a conventional oxide-mixed method and the effects of Nb-doping on microstructure, piezoelectric and ferroelectric properties of the ceramics were investigated. All the ceramics exhibit a pure perovskite structure with rhombohedral symmetry. The grain growth of the ceramics is inhibited after the addition of Nb doping. High electric insulation (R = 10⁹–10¹⁰ Ω?cm) and the poor piezoelectric performance and weak ferroelectricity are observed after the addition of Nb₂O₅ in the ceramics. Different from the donor effect of Pb-based perovskite ceramics, the introduction of Nb into 0.7BiFeO₃–0.3BaTiO₃ degrades the piezoelectricity and ferroelectricity of the ceramics. The Bi_0.7Ba_0.3(Fe_0.7Ti_0.3)_1?x Nb_0.66x O₃ + 1 mol% MnO₂ ceramic with x = 0 exhibits the optimum piezoelectric properties with d ₃₃ = 133 pN C^?1 and k _p = 0.29 and high Curie temperature (T_C = 603^°C).     

Structural and electrical properties of lead reduced lanthanum modified BiFeO<Subscript>3</Subscript>–PbTiO<Subscript>3</Subscript> solid solution

Lanthanum modified binary electronic systems of BiFeO₃ (BFO) and PbTiO₃ (PT) in different molar ratios with reduced lead (Pb) content have been synthesized by using a high-temperature solid-state reaction technique. Detailed studies of structural, morphological and electrical properties of the prepared solid solutions [(Pb_1?xBi_0.5xLa_0.5x)(Fe_xTi_1?x)O₃ with x = 0.1, 0.3, 0.5 and 0.7] have provided some interesting findings on structure-properties relationship. An abrupt change is observed in the structure of the solid solution from tetragonal to rhombohedral with the increase of La concentration. The micro-structural analysis reveals that the grain size of the system reduces on increasing La concentration of the prepared electronic system. The reduction of Pb concentration not only advances the dielectric response of lanthanum modified BiFeO₃–PbTiO₃ electronic material but also suppresses the toxic behavior of the material. For higher concentration of La, the remnant polarization is observed to be minimum. The impedance studies exhibit the presence of grain and grain boundary effects, and existence of a negative temperature coefficient of resistance (NTCR) in the material. The ac conductivity increases with increase in frequency in the low-temperature region for all the materials. It is observed that the prepared electronic materials obey the non-exponential type of conductivity relaxation.     

Effect of excess Pb on microstructures and electrical properties of 0.67Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>–0.33PbTiO<Subscript>3</Subscript> ceramics

0.67Pb(Mg_1/3Nb_2/3)O₃–0.33PbTiO₃ (PMNT) ceramics were fabricated by using their powders synthesized through a sol–gel process. Excess Pb(CH₃COO)₂·3H₂O (0, 2, 5, 10 or 15 mol%) was added to the starting materials to study the effect of excess Pb on the microstructures, ferroelectric and dielectric properties of the PMNT ceramics. All the X-ray diffraction peaks can be indexed using perovskite-type PMNT for the ceramics prepared with excess Pb, while the PMNT ceramics with no excess Pb contain a little pyrochlore phase. The PMNT ceramics prepared with 2 mol% excess Pb are dense and uniform and composed of grains ranging from 3 to 7 μm. They exhibit the largest remnant polarization (P _r = 32.1 μC/cm²) and the highest peak dielectric constant (ε _max = 12,725). When more than 2 mol% excess Pb added, the electrical properties of the PMNT ceramics decreased with increasing excess Pb. Too much excess Pb (over 10 mol%) resulted in abnormal grain growth (>20 μm), large pores and residual PbO in amorphous state in PMNT ceramics, and they impaired the ferroelectric and dielectric properties of PMNT ceramics greatly.     

Effect of low-melting additives on the structure,phase transitions,and dielectric properties of 0.36BiScO<Subscript>3</Subscript> · 0.64PbTiO<Subscript>3</Subscript> 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.     

Effects of annealing and Nb doping on the electrical properties of p-Si/n-β-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript>:Nb heterojunction

p-Si/n-β-Ga₂O₃:Nb heterojunctions were fabricated by RF magnetron sputtering of β-Ga₂O₃:Nb layers on the p-Si substrates. The effects of annealing and Nb doping on the properties of heterojunctions were studied. The crystallinity of the β-Ga₂O₃:Nb film was enhanced by annealing, which also improved the electrical properties of the heterojunctions. The Nb doping greatly affected the I–V characteristics of annealed heterojunctions. The ideality factor was calculated by performing plots from the forward bias I–V characteristics. The charge transport properties of the heterojunction were discussed. The activation energy of β-Ga₂O₃:Nb films were estimated based on the temperature dependence of resistance.     

Effect of excess Pb in PbTiO<Subscript>3</Subscript> precursors on ferroelectric and fatigue property of sol–gel derived PbTiO<Subscript>3</Subscript>/PbZr<Subscript>0.3</Subscript>Ti<Subscript>0.7</Subscript>O<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> thin films

A series of Pb_(1+x)TiO₃/PbZr_0.3Ti_0.7O₃/Pb_(1+x)TiO₃ (PTO/PZT/PTO) and PbZr_0.3Ti_0.7O₃ (PZT) thin films were prepared by a sol–gel method. Different excess Pb content (x) (x = 0, 0.05, 0.10, 0.15, 0.20) were added to the PbTiO₃ (PTO) precursors to investigate their effect on ferroelectric and fatigue properties of the PTO/PZT/PTO thin films. X-ray diffraction results show that the crystallization behavior of the PTO/PZT/PTO thin films is greatly affected by the excess Pb content (x) in PTO precursors. Topographic images show that the PTO/PZT/PTO thin films with excess Pb content x = 0.10 appears the densest and the most uniform grain size surface morphology. The ferroelectric and fatigue properties of the films correlate straightforwardly to the crystallization behaviors and excess Pb content (x) in the PTO precursors. The excess Pb content (x) in the PTO layers which acts as a nucleation site or seeding layer for PZT films affects the crystallization of the PTO layer and ultimately affects the perovskite phase formation of the PZT films. With the proper excess Pb content (x = 0.10–0.15) in the PTO precursors, the pure perovskite structure PTO/PZT/PTO thin films, with dense, void-free, and uniform fine grain size are obtained, and a well-saturated hysteresis loop with higher remnant polarization is achieved. Using an appropriate Pb content, the fatigue has been avoided by controlling the inter-diffusion and surface volatilization.     

Thermal and dielectric properties of the LTCC composites based on the eutectic system BaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The low-temperature co-fired ceramic (LTCC) composites containing quartz based on the eutectic system BaO–Al₂O₃–SiO₂–B₂O₃ are fabricated at the sintering temperature below 980 °C. Preparation process and sintering mechanism were described and discussed, respectively. The results indicated that the addition of quartz to the eutectic system can availably improve dielectric properties of the LTCC composites. In addition, The LTCC composites with optimum compositions, which were obtained by the regulation of an Al₂O₃ content in the composite, can express excellent dielectric properties (permittivity: 5.94, 5.48; loss: 7 × 10⁻⁴, 5 × 10⁻⁴), considerable CTE values (11.7 ppm. °C⁻¹, 10.6 ppm. °C⁻¹) and good mechanical properties (128 MPa,133 MPa).     

Ferroelectric and piezoelectric properties of new NaNbO<Subscript>3</Subscript>–Bi<Subscript>0.5</Subscript>K<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> lead-free ceramics

New lead-free ceramics (1–x)NaNbO₃–xBi_0.5K_0.5TiO₃ have been fabricated by the conventional ceramic sintering technique, and their ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction reveal that Bi_0.5K_0.5TiO₃ diffuses into the NaNbO₃ lattices to form a new perovskite-type solid solution with orthorhombic symmetry. The addition of a small amount of Bi_0.5K_0.5TiO₃ (x ≥ 0.025) transforms the ceramics from antiferroelectric to ferroelectric. The ceramic with x = 0.10 possesses the largest remanent polarization P _r and thus exhibits the optimum piezoelectric properties, giving d ₃₃ = 71 pC/N, k _p = 16.6% and k _t = 39.7%. The ceramics with low doping level of Bi_0.5K_0.5TiO₃ are normal ferroelectrics and the ferroelectric-paraelectric phase transition becomes diffusive gradually with the doping level x of Bi_0.5K_0.5TiO₃ increasing. Our results show the (1–x)NaNbO₃–xBi_0.5K_0.5TiO₃ ceramics is one of the good candidates for lead-free piezoelectric and ferroelectric materials.     

Structural and electrical properties of Ho<Superscript>3+</Superscript>-modified Pb(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>–9PbTiO<Subscript>3</Subscript> single crystals

Ho³⁺-modified Pb(Zn_1/3Nb_2/3)O₃–9PbTiO₃ (PZN–9PT) single crystals were grown through a flux method. Phase structure and microstructural morphology of the as-grown single crystals were performed by X-ray diffraction analysis and scanning electron microscopy. The refinement of the lattice parameters were obtained by the Rietveld method. The electrical properties of PZN–9PT single crystals were improved significantly by the modification of Ho³⁺ ions. The rhombohedral–tetragonal phase transition temperature, Curie temperature, coercive field at 15 kV cm^?1, and remnant polarization of Ho³⁺-modified PZN–9PT single crystals were increased by 14, 42 K, 2.4 kV cm^?1, and 7.5 μC cm^?2, respectively (i.e., 375.45, 448.45 K, 5.9 kV cm^?1, and 38.40 μC cm^?2, respectively). Furthermore, Lorentz-type law was used to describe the dielectric relaxor behavior of the as-grown single crystals.     

Optical properties and crystallization of glasses in the system Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–MoO<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The purpose of this work is to study the optical properties and crystallization of glasses in the ternary system Bi₂O₃–MoO₃–B₂O₃. In order to verify the obtaining of bismuth borate crystal phases several glass compositions have been selected for crystallization. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The UV–Vis spectroscopy showed that the obtained glasses are transparent in the visible region. The values of optical band gap (E _opt) and changes in cut-off (λ_c) depending on composition are reported. It was established that the increase in the MoO₃ content led to decreasing the transmittance of the glasses. Moreover, the absorption edge shifts towards longer wavelength.     

Phase formation and dielectric properties of ceramics in the BiFeO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–Bi(Mg<Subscript>0.5</Subscript>Ti<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> system

We have studied the effect of Bi(Mg_0.5Ti_0.5)O₃ additions on the phase formation, structural parameters, microstructure, and dielectric properties of solid solutions in the region of a morphotropic phase boundary in the BiFeO₃–BaTiO₃ system. Single-phase samples with the perovskite structure have been obtained and the addition of Bi(Mg_0.5Ti_0.5)O₃ has been shown to raise the Curie temperature of the ceramics and improve their dielectric properties.     

Dielectric and piezoelectric properties of Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaNb<Subscript>2</Subscript>O<Subscript>6</Subscript> lead-free piezoelectric ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xBaNb₂O₆ (BNT–BN100x), a new member of the BNT-based group, was prepared by conventional solid state reaction. X-ray diffraction showed that BaNb₂O₆ (BN) diffused into the lattice of Bi_0.5Na_0.5TiO₃ to form a solid solution with perovskite-type structure. The temperature dependence of dielectric constant ε_r revealed that the solid solution underwent two phase transitions from ferroelectric to anti-ferroelectric and anti-ferroelectric to paraelectric. Both the transition temperature T _d and T _m were shifted to lower with the increasing content of BaNb₂O₆. The temperature dependence of dielectric constant at different frequency revealed that the solid solution exhibited obviously dielectric relaxation characteristics. The sample with x = 0.6 mol% exhibited excellent electrical properties, piezoelectric constant d ₃₃ = 94 pC/N; electromechanical coupling factor k _p = 0.185. The results showed that BNT–BN100x ceramics were good candidates for use as lead-free piezoelectric ceramics.     

Structure and piezoelectric properties of new ternary K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–LiSbO<Subscript>3</Subscript>–CaTiO<Subscript>3</Subscript> lead-free piezoceramics

New ternary (1−x)K_0.5Na_0.5NbO₃–x(0.80LiSbO₃–0.20CaTiO₃) lead-free ceramics were fabricated by a conventional ceramic technique and their structure and piezoelectric properties were studied. The results of X-ray diffraction reveal that LiSbO₃ and CaTiO₃ diffuse into the K_0.5Na_0.5NbO₃ lattices to form a new solid solution with a perovskite structure. After the addition of LiSbO₃ and CaTiO₃, the cubic-tetragonal and tetragonal-orthorhombic phase transitions shift to lower temperatures. Coexistence of the orthorhombic and tetragonal phases is hence formed in the ceramics with 0.03 < x < 0.07 at room temperature, leading to a significant enhancement of the piezoelectric properties. For the ceramics with x = 0.04–0.06, the piezoelectric properties become optimum: d ₃₃ = 172–253 pC/N, k _P = 49.9–55.5%, k _t = 49.2–52.1% and T _C = 348–373 °C. The ceramic with x = 0.04 also exhibits a good thermal stability of piezoelectric properties.     

Enhanced dielectric and piezoelectric properties of (100) oriented Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–SrTiO<Subscript>3</Subscript> thin films

The (100) oriented and random oriented 0.755Bi_0.5Na_0.5TiO₃–0.065BaTiO₃–0.18SrTiO₃ (BNT–BT–ST) thin films were deposited on LaNiO₃ (LNO) buffered Pt(111)/Ti/SiO₂/Si substrates by the sol–gel processing technique. The orientation is controlled by the concentration of solution. The structure, dielectric and piezoelectric properties of the thin films are significantly affected by the crystallographic orientation. The (100) oriented BNT–BT–ST thin film has improved dielectric and piezoelectric properties. For the (100) oriented and random oriented BNT–BT–ST thin films, the dielectric constants are 660 and 550, the dielectric losses are 0.045 and 0.076 and the effective piezoelectric coefficients are 140 and 110 pm/V, respectively. The large piezoelectric response is attributed to the uniform microstructure and increased lattice distortion along (100) direction.     

Structural and electrical properties of Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–Sr<Subscript>3</Subscript>CuNb<Subscript>2</Subscript>O<Subscript>9</Subscript> lead-free piezoelectric ceramics

The structure, microstructure, field-induced strain, ferroelectric, piezoelectric and dielectric properties of (1 ? x) (Bi_0.5Na_0.5)_0.935Ba_0.065TiO₃–xSr₃CuNb₂O₉ (BNT-BT6.5–xSCN, with x = 0, 0.003, 0.006, 0.009) ceramics were investigated. X-ray diffraction patterns show that all samples are pure perovskite structure and Sr₃CuNb₂O₉ (SCN) effectively diffused into the 0.935Bi_0.5Na_0.5TiO₃–0.065BaTiO₃ (BNT–BT6.5) solid solution which also reflected in the Raman spectra and the energy disperse spectroscopy (EDS) analysis. With the increases of SCN content, the coercive field (E _c  = 18.41 kV/cm) decreases greatly, whereas the remnant polarization (P _r  = 29.11 μC/cm²) increases a little at x = 0.003 which is showed in the polarization hysteresis (P–E) loops, the result indicate that the ferroelectric order would be disrupted. Around critical composition (x = 0.003) at a driving field of 60 kV/cm, a large unipolar strain of 0.29 % with a normalized strain (d ₃₃ ^*  = 483 pm/V) is obtained at room temperature. The results indicate that BNT-BT6.5-xSCN ceramics with excellent properties are promising to replace lead-based piezoelectric ceramics and can be used in practical applications.     

Sintering and microstructure of materials based on the fluorohydroxyapatite–ZrO<Subscript>2</Subscript>–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied the influence of the sintering temperature and modifying additives on the phase composition, microstructure, and mechanical strength of a fluorohydroxyapatite-based composite ceramic material containing 20 wt % zirconia. The addition of 5 wt % alumina has been shown to prevent recrystallization processes and contribute to phase composition stabilization. Moreover, the addition of a sintering aid (2 wt %) has made it possible to lower the sintering temperature to 1200°C and raise the bending strength of the material to 143 MPa.     

Influence of cryochemical and ultrasonic processing on the texture and thermal decomposition of xerogels and properties of nanoceramics in the ZrO<Subscript>2</Subscript>〈Y<Subscript>2</Subscript>O<Subscript>3</Subscript>〉–Al<Subscript>2</Subscript>O<Subscript>3</Subscript> system

We have studied the influence of cryochemical and ultrasonic processing on the formation, structure, particle size, and thermal decomposition of xerogels in the ZrO₂〈Y₂O₃〉–Al₂O₃ (20 wt %) system. Nanopowders of tetragonal-zirconia-based solid solutions with a high degree of tetragonality (c/a = 1.4366) have been synthesized. Al₂O₃ has been shown to slow down t-ZrO₂ crystallite growth in the temperature range 600–1400°C. We have optimized nanopowder consolidation conditions, obtained nanoceramics stable to low-temperature “aging” in a humid medium, and investigated their physicochemical and mechanical properties.     

Crystal structure and properties of BaTiO<Subscript>3</Subscript>–(Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript> ceramic system

(1 − x)BaTiO₃–x(Bi_0.5Na_0.5)TiO₃ (x ranged from 0.01 to 0.96) ceramics were fabricated by the conventional ceramic technique. The crystal structure, as well as dielectric and piezoelectric properties of the ceramics were studied. All the ceramics formed single-phase solid solutions with perovskite structure after sintering in air at 1150–1250 °C for 2–4 h. The crystal structure and microstructure varied gradually with the increase of (Bi_0.5Na_0.5)TiO₃ (BNT) content. The Curie temperature, T _c, shifted monotonously to high temperature as BNT increased. The ceramics with 20–90 mol% BNT had relatively low and stable dielectric loss characteristics. The piezoelectric constant, d ₃₃, enhanced with the increase of BNT content through a maximum value in a composition of 93 mol% BNT and then tended to decrease. The maximum value, 148 pC/N, of piezoelectric constant d ₃₃ together with the electromechanical coupling factors, k _t, 19.8% and k _p, 15.8%, were obtained when BNT was 93 mol%.