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.     

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%.     

Fabrication of lead-free piezoelectric (Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript> ceramics using electrophoretic deposition

Electrophoretic deposition (EPD) process has certain advantages such as it can be applied for a mass production and also can be combined with magnetic crystal alignment technique. In this work, we prepared lead-free 85(Bi_0.5Na_0.5)TiO₃–15BaTiO₃ (85BNT–15BT) piezoelectric ceramics by conventional uniaxial pressing and EPD process. Various conditions were optimized such as suspension media, applied electrical field, and deposition time in order to yield dense green ceramics of 85BNT–15BT composition using EPD process. 85BNT–15BT ceramics prepared using EPD process revealed the Curie temperature of about 250 °C, coercive field of about 30 kV/cm, and piezoelectric constant (d ₃₃) of 75 pC/N. The EPD-processed samples exhibited structural and electrical properties similar to that of the conventionally processed one suggesting the successful fabrication of 85BNT–15BT piezoelectric ceramics by EPD method without composition deviation. This study lays a foundation on the fabrication of Bi-based lead-free piezoelectric ceramics by an alternative route other than the conventionally practiced solid-state reaction method maintaining the similar chemical composition, moreover, leaving a large space to explore more in the future.     

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.     

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.     

Synthesis and piezoelectric properties of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> ceramics prepared by sol–gel auto-combustion method

In this study, NaNO₃, Bi(NO₃)₃·5H₂O, Ba(NO₃)₂, Ti(OC₄H₉)₄ and citric acid were successfully introduced to fabricate lead-free piezoelectric (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ [NBBT] nanopartical powders by a novel modified sol–gel auto-combustion method. The resultant products were characterized by the X-ray diffraction analysis and transmission electron microscope method. (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ + Mn(NO₃)₂ [NBBTM] can be sintered by the traditional solid-state reaction, and the effects of NBBT doped different amounts of Mn(NO₃)₂ at various sintering temperatures upon phase formation, microstructure as well as piezoelectric properties were further studied. The experimental results show that it was helpful to control their chemical ingredients and microstructure to prepare nanocrystalline single phase NBBT powders. Where is the X-ray diffraction result of the corresponding ceramics to prove the existence of the mixing between rhombohedral and tetragonal phases at the MPB compositions. Doping 0.015 mol% Mn(NO₃)₂ into NBBT at 1,090 °C, piezoelectric constant (d ₃₃) and relative dielectric constant (ε_r) reach the superior value of 159pC/N and 1,304, respectively, and dielectric loss (tan δ) and electromechanical coupling factor (K _t) are 2.5% and 65%, respectively.     

Two-step sintering and electrical properties of sol–gel derived 0.94(Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript>–0.06BaTiO<Subscript>3</Subscript> lead-free ceramics

Two-step pressureless sintering of sol–gel derived 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ (BNT-BT) lead-free piezoelectric ceramics were investigated in comparison with conventional sintering. The effect of sintering regimes on the densification, grain growth behavior and electrical properties was discussed in detail. The results indicated that BNT-BT ceramics with a density of 95%, a relatively fine grain size of 850 nm and comparable piezoelectric properties (d₃₃ ~170 pC/N, k_p ~0.26, Q_m ~102) had been achieved by pre-sintering at 1,150 °C to reach a critical density of 78%, and then cooling to a lower temperature of 1,050 °C for 20 h. The critical density value proves important at which the grain boundary diffusion could be maintained but the grain boundary migration suppressed at the same time. Moreover, the volatilization loss of Bi and Na elements could be inhibited by two-step sintering. Both the reduction of the grain size and the inhibition of the stoichiometry deviation together account for the variation of various electrical properties.     

Piezoelectric properties of [Bi<Subscript>0.5</Subscript>(Na<Subscript>0.7</Subscript>K<Subscript>0.25</Subscript>Li<Subscript>0.05</Subscript>)<Subscript>0.5</Subscript>]TiO<Subscript>3</Subscript>−Ba(Ti,Zr)O<Subscript>3</Subscript> binary system ceramics

Dense lead-free binary system piezoelectric ceramics (1 − x)[Bi_0.5(Na_0.7K_0.25Li_0.05)_0.5]TiO₃−xBa(Ti_0.95Zr_0.05)O₃ (BNKLT–BZT) were prepared by a two-step sintering process. A phase transition from rhombohedral to tetragonal was observed with increasing BZT fraction in the range x = 0.06–0.1 and the morphotropic phase boundary (MPB) between rhombohedral and tetragonal appears in this range. Ceramics containing 10 mol% BZT with tetragonal phase near the MPB region has the maximum piezoelectric constant d ₃₃(151pC/N).     

Poling effects and piezoelectric properties of PVDF-modified 0–3 connectivity cement-based/lead-free 0.94(Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript>–0.06BaTiO<Subscript>3</Subscript> piezoelectric ceramic composites

PVDF-modified 0–3 connectivity cement-based/lead-free 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ piezoelectric ceramic composites were fabricated using 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ (BNBT), Portland cement, and polyvinylidene fluoride (PVDF). The microstructure, acoustic impedance (Z _c), dielectric properties, and influence of poling temperature and electrical poling field on the piezoelectric coefficient (d ₃₃) and the total period of the poling process of composites with 50 vol% BNBT and 1–10 vol% PVDF were investigated. The results indicated that Z _c, the dielectric constant, and the dielectric loss of the composites decrease as the PVDF content increases. The d ₃₃ of the composites was found to enhance more clearly when the content of PVDF is more than 2 vol%. The d ₃₃ results of the composites showed an optimum increase of 45% when 5 vol% PVDF was used (under an electrical poling field of 1.5 kV/mm and a poling temperature of 80°C). Moreover, these composites with PVDF were found to exhibit enhanced poling behavior in that the PVDF was able to reduce the total period of the poling process. Interestingly, the piezoelectric voltage coefficient (g ₃₃) of the composite with 5 vol% PVDF content had the highest value of 33.59 mV·m/N. Therefore, it can be safely concluded that this new kind of PVDF-modified 0–3 connectivity cement-based/lead-free 0.94(Bi_0.5Na_0.5)TiO₃–0.06BaTiO₃ piezoelectric ceramic composite has the potential to be used in concrete as a sensor for structural health monitoring applications.     

Preparation and properties of Bi<Subscript>6</Subscript>Ti<Subscript>5</Subscript>WO<Subscript>22</Subscript>: a new phase in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> system

In a recent report, the evaluation of the phase relations in the Bi₂O₃–TiO₂–WO₃ ternary system has shown the existence of a new phase with nominal composition close to Bi₆Ti₅WO₂₂. In the present contribution we attempt to prepare this single phase by using a solid state route. Although XRD analyses also show traces of two minority Aurivillius-type phases in the synthesized materials, the crystal structure of the Bi₆Ti₅WO₂₂ phase has been determined by Rietveld analyses revealing a complex structure similar to that of Bi₃(AlSb₂)O₁₁ and PbHoAl₃O₈ related compounds. The electrical response of this new phase was characterized as well. Three peaks are observed in its dielectric response: two of them positioned around 0 °C and can be assigned to this Bi₆Ti₅WO₂₂ structure. The third one rises up to 665 °C and confirms the presence of the Aurivillius-type phases.     

Synthesis,microstructure, and electrical behavior of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> piezoelectric ceramics via a citric acid sol–gel method

Nanosize (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ precursor powders were prepared via the citric acid sol–gel method. The ceramics were sintered at 1100–1150 °C. All ceramics exhibit a single-phase perovskite structure. With increasing sintering temperature, the average size of grains in the samples changes slightly from 0.3 to 0.5 µm. All ceramics show obvious dielectric dispersion. Activation energy values were obtained via impedance, electric modulus, and conductivity, respectively, which are in the range of 0.60–1.06 eV. Compared to ceramics synthesized by solid-state reaction method, the as-synthesized samples are fine-grained and have high depolarization temperature and excellent temperature stability of the piezoelectric constant (d ₃₃). The d ₃₃ value of the sample sintered at 1120 °C remains as high as 119 pC N^?1 with increasing annealing temperature to 115 °C, whereas the reduced amplitude of d ₃₃ is only approximately 3%.     

Effect of mechanical depoling on piezoelectric properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>–<Emphasis Type="Italic">x</Emphasis>BaTiO<Subscript>3</Subscript> in the morphotropic phase boundary region

The effect of mechanical stress on the direct piezoelectric properties of pre-poled (1 ? x)(Na_0.5Bi_0.5)TiO₃–xBaTiO₃ (NBT–xBT) in the range 4% ≤ x ≤ 13% was studied in situ using a mechanical load frame. Prior to mechanical loading, compositions near the morphotropic phase boundary (MPB, x = 6–7% BT) exhibited enhanced ferroelectric and piezoelectric properties compared to compositions further from the MPB. Specifically, the lowest ferroelectric coercive field and highest piezoelectric coefficient within this composition range occur at x = 7% BT. During mechanical compression, the MPB compositions exhibited the lowest depoling stress. The results demonstrate that, while favorable piezoelectric and ferroelectric properties can be obtained at compositions near the MPB, these compositions are also the most susceptible to the effects of mechanical depoling. Ferroelastic domain wall motion is suggested as the primary factor that may be responsible for these behaviors.     

Phase formation and dielectric properties of Ba<Subscript>0.5</Subscript>Sr<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> by slow injection sol–gel technique

A simple sol–gel process incorporating slow precursor injection technique was employed to synthesize homogeneous Ba_0.5Sr_0.5TiO₃ nano powders. The Ba_0.5Sr_0.5TiO₃ samples were subjected to calcination temperatures from 600 to 1,100 °C and sintering temperatures from 1,250 to 1,350 °C for the study of phase formation, crystallite size, particle distribution, and dielectric properties. Single phase Ba_0.5Sr_0.5TiO₃ with a cubic perovskite structure was successfully synthesized after calcination at 800 °C. The average size of the nano particles is 42 nm with a narrow size distribution, and a standard deviation of 10%. The highest values recorded within the investigated range for dielectric constant, and dielectric loss measured at 1 kHz are 1,164 and 0.063, respectively, for Ba_0.5Sr_0.5TiO₃ pellets calcined at 800 °C and sintered at 1,350 °C. Leakage current density measured at 5 V for the Ba_0.5Sr_0.5TiO₃ pellet was found to be 49.4 pA/cm².     

Synthesis and characterization of TiO<Subscript>2</Subscript>–NiO and TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> nanocomposites

TiO₂–NiO and TiO₂–WO₃ nanocomposites were prepared by hydrothermal and surface modification methods. The samples were analyzed using X-ray diffraction, Scanning Electron Microscope images, Transmission Electron Microscope, Energy dispersive analysis, Zeta potential, Electrophoretic mobility and Photocatalysis activity measurement. XRD data sets of TiO₂–NiO, TiO₂–WO₃ powder nanocomposite have been studied for the inclusion of NiO, WO₃ on the anatase-rutile mixture phase of TiO₂ by Rietveld refinement. The cell parameters, phase fraction, the average grain size, strain and bond lengths between atoms of individual phases have been reported in the present work. Shifted positional co-ordinates of individual atoms in each phase have also been observed.     

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.     

Enhanced microwave dielectric properties of Ba<Subscript>0.40</Subscript>Sr<Subscript>0.60</Subscript>TiO<Subscript>3</Subscript>–Zr<Subscript>0.80</Subscript>Sn<Subscript>0.20</Subscript>TiO<Subscript>4</Subscript> composite ceramics

The (1−x) Ba_0.40Sr_0.60TiO₃ (BST)−xZr_0.80Sn_0.20TiO₄ (ZST) composite ceramics with x = 10, 20, 30, and 40 wt% were fabricated by conventional solid-state reaction method. With increasing of ZST content, the dielectric constant of composite ceramics was decreased and dielectric loss increases. The effect of ZnO addition to 70 wt% BST–30 wt% ZST composition on the microstructure and dielectric properties was investigated. The improvements in dielectric constant, dielectric loss, and microwave dielectric properties of composite ceramics can be achieved by ZnO addition. The sample with 98 wt% (70 wt% BST–30 wt% ZST)–2 wt%ZnO composition exhibits promising dielectric properties, with dielectric constant, loss tangent and tunability at 4 kV/mm, of 125, 0.0016 and 12%, at 10 kHz and room temperature. At ~2 GHz, it possesses a dielectric constant of 101 and a Q factor of 187, which makes it a good candidate for tunable microwave device applications.     

Dielectric and piezoelectric properties of Bi<Subscript>0·5</Subscript>(Na<Subscript>0·82</Subscript>K<Subscript>0·18</Subscript>)<Subscript>0·5</Subscript> TiO<Subscript>3</Subscript>-LiSbO<Subscript>3</Subscript> lead-free piezoelectric ceramics

The (1−x)Bi_0·5(Na_0·82K_0·18)_0·5TiO_3−x LiSbO₃ (x = 0−0·03) lead-free piezoelectric ceramics were fabricated by a conventional solid-state reaction method and the effect of LiSbO₃ addition on microstructure and electrical properties of the ceramics was investigated. The results of XRD measurement show that Li⁺ and Sb⁵⁺ diffuse into the Bi_0·5(Na_0·82K_0·18)_0·5TiO₃ lattices to form a solid solution with a pure perovskite structure. The LiSbO₃ addition has no remarkable effect on the crystal structure. However, a significant change in grain size took place. Simultaneously, with increasing amount of LiSbO₃, the temperature for a antiferroelectric to paraelectric phase transition clearly increases. The piezoelectric constant d ₃₃ and the electromechanical coupling factor k _p show an obvious improvement by adding small amount of LiSbO₃, which shows optimum values of d ₃₃ = 175 pC/N and k _p = 0·36 at x = 0·01.     

Self-intercalation in Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>〈Cu〉

We have studied the electronic properties of Bi₂Te₃〈Cu〉 crystals. The results indicate that, during natural growth and subsequent self-intercalation, copper layers are formed between Te(I)-Te(I) layers in the basal plane (0001). On cleaved (0001) surfaces, quasi-two-dimensional layers with islands were found. Studies of Shubnikov-de Haas-like 4.2-K magnetoresistance oscillations in Bi₂Te₃〈Cu〉 revealed additional series of oscillations for H ⊥ C ⊥ I. We observed magnetoresistance oscillations at temperatures from 240 to 280 K, due to the magnetophonon resonance. The magnetophonon oscillations in self-intercalated Bi₂Te₃〈Cu〉 are periodic and better defined in comparison with copper-intercalated Bi₂Te₃.     

Microwave dielectric properties of temperature-stable (Mg<Subscript>0.95</Subscript>Co<Subscript>0.05</Subscript>)<Subscript>2</Subscript>TiO<Subscript>4</Subscript>–Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript> composite ceramics for LTCC applications

In this paper, the effects of Li₂O–B₂O₃–Bi₂O₃–SiO₂ (LBBS) glass on the phase formation, sintering characteristic, the microstructure and microwave dielectric properties of temperature-stable (Mg_0.95Co_0.05)₂TiO₄–Li₂TiO₃ ceramics were investigated. (Mg_0.95Co_0.05)₂TiO₄–Li₂TiO₃ powders were obtained by using the traditional solid-state process. A small amount of LBBS doping can effectively reduce sintering temperature and promote the densification of the ceramics. X-ray diffraction analysis revealed not only the primary phase (Mg·Co)₂TiO₄ associated with Li₂TiO₃ minor phase but also a third phase (Mg·Co)TiO₃. The dielectric constant and Qf values vary with the doping amount of LBBS and sintering temperatures. With the compensation of the positive temperature coefficient (τ _f ) of Li₂TiO₃ and the negative τ _f of (Mg_0.95Co_0.05)₂TiO₄, the τ _f of the specimens fluctuates around zero. The (Mg_0.95Co_0.05)₂TiO₄ ceramic with 2.5 wt% LBBS addition and sintering at 900?°C for 4 h exhibited excellent microwave dielectric properties: ? _r ?=?19.076, Qf?=?126100 GHz, and τ _f ?=?0.98 ppm/°C.     

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.