BiScO3 Doped (Na0.5K0.5)NbO3 Lead-Free Piezoelectric Ceramics

Lead-free potassium sodium niobate-based piezoelectric ceramics (1− x )(Na_0.5K_0.5)NbO₃– x BiScO₃ (KNN–BS) ( x =0∼0.05) have been prepared by an ordinary sintering process. Single perovskite phase of KNN–BS exhibits an orthorhombic symmetry at x <0.015 and pseudocubic symmetry at x >0.02, separating by a MPB at 0.015≤ x ≤0.02. Piezoelectric and ferroelectric properties are significantly enhanced in the MPB, which are as follows: piezoelectric constant d ₃₃=203 pC/N, planar coupling coefficient k _p=0.36, remnant polarization P _r=24.4 μC/cm². These solid solution ceramics look promising as a potential lead-free candidate materials.     

In-Plane Polarized 0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 Thin Films

Ferroelectric 0.7Pb(Mg_1/3Nb_2/3)O₃–0.3PbTiO₃ (PMN-PT) thin films were deposited on ZrO₂/SiO₂/silicon substrates using a chemical-solution-deposition method. Using a thin PZT film as a seed layer for the PMN-PT films, phase-pure perovskite PMN-PT could be obtained via rapid thermal annealing at 750°C for 60 s. The electrical properties of in-plane polarized thin films were characterized using interdigitated electrode arrays on the film surface. Ferroelectric hysteresis loops are observed with much larger remanent polarizations (∼24 μC/cm²) than for through-the-thickness polarized PMN-PT thin films (10–12 μC/cm²) deposited on Pt/Ti/Si substrates. For a finger spacing of 20 μm, the piezoelectric voltage sensitivity of in–plane polarized PMN-PT thin films was ∼20 times higher than that of through-the-thickness polarized PMN-PT thin films.     

Sintering and Electrical Properties of Lead-Free Na0.5K0.5NbO3 Piezoelectric Ceramics

Lead-free Na_0.5K_0.5NbO₃ (NKN) piezoelectric ceramics were fairly well densified at a relatively low temperature under atmospheric conditions. A relative density of 96%–99% can be achieved by either using high-energy attrition milling or adding 1 mol% oxide additives. It is suggested that ultra-fine starting powders by active milling or oxygen vacancies and even liquid phases from B-site oxide additives mainly lead to improved sintering. Not only were dielectric properties influenced by oxide additives, such as the Curie temperature ( T _c) and dielectric loss ( D ), but also the ferroelectricity was modified. A relatively large remanent polarization was produced, ranging from 16 μC/cm² for pure NKN to 23 μC/cm² for ZnO-added NKN samples. The following dielectric and piezoelectric properties were obtained: relative permittivity ɛ ^T ₃₃/ɛ ₀ =570–650, planar mode electromechanical coupling factor, k _p=32%–44%, and piezoelectric strain constant, d ₃₃=92–117 pC/N.     

K/Na Ratio Dependence of the Electrical Properties of [(KxNa1−x)0.95Li0.05](Nb0.95Ta0.05)O3 Lead-Free Ceramics

[(K _x Na_{1− x} )_0.95Li_0.05](Nb_0.95Ta_0.05)O₃ (K _x NLNT) ( x= 0.40–0.60) lead-free piezoelectric ceramics were prepared by conventional solid-state sintering. The effects of K/Na ratio on the dielectric, piezoelectric, and ferroelectric properties of the K _x NLNT ceramics were studied. The experimental results show that the electrical properties strongly depend on the K/Na ratio in the K _x NLNT ceramics. The K _x NLNT ( x =0.42) ceramics exhibit enhanced properties ( d ₃₃∼242 pC/N, k _p∼45.7%, k _t∼47%, T _c∼432°C, T _o−t =48°C, ɛ_r∼1040, tanδ∼2.0%, P _r∼26.4 μC/cm², E _c∼10.3 kV/cm). Enhanced electrical properties of the K _x NLNT ( x =0.42) ceramics could be attributed to the polymorphic phase transition near room temperature. These results show that the K _x NLNT ( x =0.42) ceramic is a promising lead-free piezoelectric material.     

Phase Structure and Electrical Properties of (K0.48Na0.52)(Nb0.95Ta0.05)O3-LiSbO3 Lead-Free Piezoelectric Ceramics

(1− x )(K_0.48Na_0.52)(Nb_0.95Ta_0.05)O₃– x LiSbO₃ [(1− x )KNNT− x LS] lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method. A morphotropic phase boundary (MPB) between orthorhombic and tetragonal phases was identified in the composition range of 0.03< x <0.05. The ceramics near the MPB exhibit a strong compositional dependence and enhanced electrical properties. The (1− x )KNNT– x LS ( x =0.04) ceramics exhibit good electrical properties ( d ₃₃=250 pC/N, k _p=45.1%, k _t =46.3%, T _c=348°C, T _{o − t} =74°C, P _r=25.9 μC/cm², E _c=10.7 kV/cm, ɛ_r∼1352, tan δ∼3%). These results show that (1− x )KNNT– x LS ceramic is a promising lead-free piezoelectric material.     

Ferroelectric and Dielectric Properties of Pb(Mg1/3Ta2/3)0.7Ti0.3O3 Thin Films Derived from RF Magnetron Sputtering

Pb(Mg_1/3Ta_2/3)_0.7Ti_0.3O₃ thin films of single perovskite phase were successfully synthesized by using the RF sputtering deposition technique, followed by post-thermal annealing. While the perovskite structure of Pb(Mg_1/3Ta_2/3)_0.7Ti_0.3O₃ is rather unstable, phase evolution in the thin films was manipulated by controlling both working pressure during the sputtering process and post-thermal annealing temperature. The desirable perovskite phase was promoted by increasing the working pressure in the range of 10–25 mTorr, followed by thermal annealing at 600°C. The ferroelectric, dielectric, and polarization behaviors of Pb(Mg_1/3Ta_2/3)_0.7Ti_0.3O₃ films were characterized over a wide range of frequencies. They are strongly affected by the film thickness, where the relative permittivity and remanent polarization increase, while the coercive field decreases with increasing film thickness in the range of 115–360 nm.     

Lanthanum-Modified (1 – x)(Bi0.8La0.2)(Ga0.05Fe0.95)O3·xPbTiO3 Crystalline Solutions: Novel Morphotropic Phase-Boundary Lead-Reduced Piezoelectrics

(1 – x )(Bi_0.8La_0.2)(Ga_0.05Fe_0.95)O₃· x PbTiO₃ (BLGF-PT) crystalline solutions have been fabricated by solid-state reactions. BLGF-PT has single perovskite phase structure with a rhombohedral–tetragonal (FE_r-FE_t) morphotropic phase boundary (MPB) at a PT content of x = 0.43. Lanthanum substitution has been found to increase the insulation resistance and decrease the coercive field down to 20 kV/cm, which results in significant improvements in dielectric and piezoelectric properties of BLGF-PT. The dielectric constant, loss tangent, Curie temperature, remnant polarization, piezoelectric d ₃₃ constant, and planar coupling factor of 1760, 0.05, 264°C, 33 μC/cm², 295 pC/N, and 0.36, respectively, have been achieved for BLFG-PT in the vicinity of the MPB. Compared with conventional Pb(Zr,Ti)O₃ (PZT) piezoelectric ceramics, the BLGF-PT is a competitive alternative piezoelectric material with decreased lead content.     

Characterization of Photoluminescent (Y1–xEux)2O3 Thin Films Prepared by Metallorganic Chemical Vapor Deposition

The purpose of this study was to identify and correlate the microstructural and luminescence properties of europium-doped Y₂O₃ (Y_{1– x} Eu _x )₂O₃ thin films deposited by metallorganic chemical vapor deposition (MOCVD), as a function of deposition time and temperature. The influence of deposition parameters on the crystallite size and microstructural morphology were examined, as well as the influence of these parameters on the photoluminescence emission spectra. (Y_{1– x} Eu _x )₂O₃ thin films were deposited onto (111) silicon and (001) sapphire substrates by MOCVD. The films were grown by reacting yttrium and europium tris(2,2,6,6-tetramethyl–3,5-heptanedionate) precursors with an oxygen atmosphere at low pressures (5 torr (1.7 × 10³ Pa)) and low substrate temperatures (500°–700°C). The films deposited at 500°C were smooth and composed of nanocrystalline regions of cubic Y₂O₃, grown in a textured [100] or [110] orientation to the substrate surface. Films deposited at 600°C developed, with increasing deposition time, from a flat, nanocrystalline morphology into a platelike growth morphology with [111] orientation. Monoclinic (Y_{1– x} Eu _x )₂O₃ was observed in the photoluminescence emission spectra for all deposition temperatures. The increase in photoluminescence emission intensity with increasing postdeposition annealing temperature was attributed to the surface/grain boundary area-reduction effect.     

Multiferroic Properties of Single-Phase Bi0.85La0.15FeO3 Lead-Free Ceramics

Single-phase and lead-free Bi_0.85La_0.15FeO₃ multiferroic ceramics were prepared by a rapid liquid sintering method to study their crystal structure and multiferroic behaviors. Rietveld refinement of X-ray diffraction data showed a pseudo-cubic structure plus a small triclinic distortion. The absence of Fe²⁺ ions suggested few oxygen vacancies. Large polarizations of 20.3 μC/cm² together with a piezoelectric d ₃₃ coefficient of ∼27.7 pC/N were achieved. This ferroelectricity originates from the stereochemical activity of the A-site Bi³⁺ lone electron pair. The remnant magnetizations of 0.0744–0.227 emu/g of Bi_0.85La_0.15FeO₃ permitted by the canting angle of canted antiferromagnetic order was released as a result of the collapse of the space-modulated spin structure of BiFeO₃. The observed dielectric anomalies proved the magnetoelectric couplings between ferroelectric order and canted antiferromagnetic order.     

Effect of MnO2 Addition on the Structure and Electrical Properties of Pb(Zn1/3Nb2/3)0.20(Zr0.50Ti0.50)0.80O3 Ceramics

Pb(Zn_1/3Nb_2/3)_0.20(Zr_0.50Ti_0.50)_0.80O₃ ceramics of pure perovskite structure were prepared by the two-stage method with the addition of 0–3.0 wt% MnO₂ and their piezoelectric properties were investigated systematically. The MnO₂ addition influences in a pronounced way both the crystal structure and the microstructure of the materials. The materials are transformed from the tetragonal to the rhombohedral structure, and the grain size is enhanced when manganese cations are added. The distortion of crystal structure for samples with MnO₂ addition can be explained by the Jahn–Teller effect. The values of electromechanical coupling factor ( k _p) and dielectric loss (tan δ) are optimized for 0.5-wt%-MnO₂-doped samples ( k _p= 0.60, tan δ= 0.2%) and the mechanical quality factor ( Q _m) is maximized for 1.0-wt%-MnO₂-doped samples ( Q _m= 1041), which suggests that oxygen vacancies formed by substituting Mn³⁺ and Mn²⁺ ions for B-site ions (e.g., Ti⁴⁺ and Zr⁴⁺ ions) in the perovskite structure partially inhibited polarization reversal in the ferroelectrics. The ceramics with 0.50–1.0 wt% MnO₂ addition show great promise as practical materials for piezoelectric applications.     

Phase Transition and Ferroelectric Characteristics of Pb[(Mg1/3Nb2/3)1-xTix]O3 Ceramics Modified with La(Mg2/3Nb1/3)O3

The effects of 0–5 mol% addition of La(Mg_2/3Nb_1/3)O₃ (LMN) on the phase transition and ferroelectric behaviors of Pb[(Mg_1/3Nb_2/3)_1-xTi_x]O₃ (PMNT) ceramics with compositions near the morphotropic phase boundary (MPB) were studied. An evolution of structure from rhombohedral to tetragonal was found with increasing PbTiO₃ (PT) content across the MPB (at ∼32.5 mol% PT), and a coexistence of both rhombohedral and tetragonal phases was also found at the MPB. The dual-phase field extended toward the lower PT content side of the MPB, and, moreover, the rhombohedrality or tetragonality was reduced, especially for the compositions near the MPB, by the addition of La in PMNT. The ferroelectric transition was found to change from normal to diffuse as the La content increased and the compositions became more rhombohedral. In accordance with the structural evolution, the change of remanent polarization ( P _r) and coercive field ( E _c) also became gradually indistinct, and both P _r and E _c were reduced. For compositions near the MPB, both PMNT and La-modified PMNT had a similar electromechanical factor ( k _p) in a range around 0.55–0.60, but the mechanical quality factor ( Q _m) was significantly reduced for the La-modified PMNT. The piezoelectric coefficient ( d ₃₃), however, was largely improved with increasing La content in PMNT of compositions at MPB. A high value of d ₃₃∼ 815 pC/N was obtained for the 5-mol%-La-modified ceramics, but it was associated with a low value of Q _m.     

Crystal Structure and Dielectric Properties of LaYbO3

The crystal structure and dielectric properties of LaYbO₃ ceramics prepared by the mixed-oxide route have been investigated. Rietveld refinements performed on X-ray and neutron diffraction data show the room-temperature structure to be best described by the orthorhombic Pnma space group [ a =6.02628(9) Å, b =8.39857(11) Å, and c =5.82717(7) Å; Z =4, and theoretical density, D _x =8.1 g/cm³] in agreement with electron diffraction experiments. LaYbO₃ ceramics fired at 1600°C for 4 h attain ∼97% of D _x and their microstructures consist of randomly distributed equiaxed grains with an average size of ∼8 μm. Conventional transmission electron microscopy shows densification to occur in the absence of a liquid phase and reveals domain-free grains. The relative permittivity, ɛ_r, of LaYbO₃ ceramics at radio frequencies is ∼26 in the range ∼10–300 K; however, a small dielectric anomaly is detected at ∼15 K. At room temperature and microwave frequencies, LaYbO₃ ceramics exhibit ɛ_r∼26, Q × f _r∼20 613 GHz (at 7 GHz), and τ_f∼−22 ppm/K. Q × f _r show complex subambient behavior, decreasing from a plateau value of ∼20 000 GHz between ∼300 and 200 K to a second plateau value of ∼6000 GHz at ∼90 K before decreasing to <1000 GHz at ∼10 K. The large decrease in Q × f _r at low temperature may be related to the onset of antiferromagnetism at ∼2.7 K. ¹     

Phase Transitions and Electrical Properties of (Na1−xKx)(Nb1−ySby)O3 Lead-Free Piezoelectric Ceramics With a MnO2 Sintering Aid

Lead-free piezoelectric ceramics (Na_{1− x} K _x )(Nb_{1− y} Sb _y )O₃+ z mol% MnO₂ have been prepared by a conventional solid-state sintering technique. Our results reveal that Sb⁵⁺ diffuses into the K_0.5Na_0.5NbO₃ lattices to form a solid solution with a single-phase orthorhombic perovskite structure. The partial substitution of Sb⁵⁺ for B-site ion Nb⁵⁺ decreases the paraelectric cubic-ferroelectric tetragonal phase transition ( T _c) and the ferroelectric tetragonal-ferroelectric orthorhombic phase transition ( T _O–F), and retains strong ferroelectricity. A small amount of MnO₂ is enough to improve the densification of the ceramics. The co-effects of MnO₂ doping and Sb substitution lead to significant improvements in ferroelectric and piezoelectric properties. The ceramics with x =0.45–0.525, y =0.06–0.08, and z =0.5–1 exhibit excellent ferroelectric and piezoelectric properties: d ₃₃=163–204 pC/N, k _P=0.47–0.51, k _t=0.46–0.52, ɛ=640–1053, tan δ=1.3–3.0%, P _r=18.1–22.6 μC/cm², E _c=0.72–0.98 kV/mm, and T _C=269°–314°C.     

Processing and Electrical Properties in Lead-Based (Pb(Mg1/3Nb2/3)O3, Pb(Yb1/2Nb1/2)O3, PbTiO3) Systems

Lead-based ferroelectric (FE) ceramics exhibit superior electromechanical properties; therefore, there has been an increased focus on developing new lead-based FE materials with high Curie temperature ( T _c) and enhanced properties. The aim of this study was to investigate new compositions in the Pb(Mg_1/3Nb_2/3)O₃–Pb(Yb_1/2Nb_1/2)O₃–PbTiO₃ ( PMN–PYbN–PT) system to enhance the electromechanical properties while increasing the T _c and lowering the sintering temperature. The 0.575[0.5PMN–0.5PYbN]–0.425PT composition at PMN/PYbN (50/50) mole ratio were prepared by reactive sintering PMNT and PYbNT powder mixtures at 950°–1200°C for 4 h. PMNT and PYbNT powders were calcined via the columbite method. Samples were prepared by cold isostatic pressing at 80 MPa. Dense and fully perovskite 0.575[0.5PMN–0.5PYbN]–0.425PT ceramics were fabricated at 975°C for 4 h, and these samples displayed a remnant polarization ( P _r) of 32 μ C/cm², coercive field ( E _c) of 17 kV/cm, and a piezoelectric charge coefficient ( d ₃₃) of 475 pC/N. It is proposed that this ternary system can be tailored for various applications.     

Piezoelectric Properties of (1−x)(Na0.5K0.5)NbO3–xAgSbO3 Lead-Free Ceramics

(1− x )(Na_0.5K_0.5)NbO₃– x AgSbO₃ lead-free piezoelectric ceramics were prepared by normal sintering. The effects of the AgSbO₃ on the phase structure and piezoelectric properties of the ceramics were systematically studied. These results show that the AgSbO₃-modified (K_0.50Na_0.50)NbO₃ lead-free piezoelectric ceramics form stable solution with orthorhombic structure, and the Curie temperature and the polymorphic phase transition of the ceramics decreased with increasing AgSbO₃. The result shows that the piezoelectric properties of the ceramics strongly depend on the AgSbO₃. The ceramics with x =0.05 possess optimum properties ( d ₃₃=192 pC/N, k _p=43%, T _c=348°C, T _o−t =145°C, ɛ_r∼632, and tan δ∼3.5%). These results indicate that the ceramic is a promising candidate material for lead-free piezoelectric ceramics.     

Elastic, Piezoelectric, and Dielectric Properties of 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 Crystals Obtained by Solid-State Crystal Growth

Single crystals with the composition of 0.71Pb(Mg_1/3Nb_2/3)O₃–0.29PbTiO₃ (PMNT29) were grown using the solid-state crystal growth (SSCG) method. Compared with the conventional Bridgman grown crystals, the SSCG PMNT29 crystals were found to possess comparable piezoelectric, dielectric, and electromechanical properties ( d ₃₃∼1500 pC/N, ɛ^T ₃₃/ ɛ ₀∼5400 and k ₃₃∼90%), with the same Curie temperature ( T _C) and ferroelectric phase transformation temperature ( T _{R – T} ). The full set of elastic, piezoelectric, and dielectric material constants were determined by the resonance method for the SSCG grown PMNT29 crystals according to IEEE standards and compared with Bridgman grown crystals. The dielectric temperature behavior and the strain field characteristics were investigated, demonstrating excellent performance over the temperature range from room temperature to 95°C. Strain behavior at high electric fields was found to be different from Bridgman growth crystals and believed to be attributed to different domain structures.     

Reduced Dielectric Loss of Modified ZnNb2O6 Ceramics by Substituting Nb5+ with Ta5+

The effects of substituting Nb⁵⁺ with Ta⁵⁺ on the microwave dielectric properties of the ZnNb₂O₆ ceramics were investigated in this study. The forming of Zn(Nb_{1− x} Ta _x )₂O₆ ( x =0–0.09) solid solution was confirmed by the measured lattice parameters and the EDX analysis. By increasing x , not only could the Q × f of the Zn(Nb_{1− x} Ta _x )₂O₆ ( x =0–0.09) solid solution be tremendously boosted from 83 600 GHz at x =0 to a maximum 152 000 GHz at x =0.05, the highest ɛ_r∼24.6 could also be achieved simultaneously. It was mainly due to the uniform grain morphology and the highest relative density of the specimen. A fine combination of microwave dielectric properties (ɛ_r∼24.6, Q × f ∼152 000 GHz at 8.83 GHz, τ_f∼–71.1 ppm/°C) was achieved for Zn(Nb_0.95Ta_0.05)₂O₆ solid solution sintered at 1175°C for 2 h.     

Chemical Solution Deposition of (Pb1−xCax)TiO3 Thin Films with x∼0.5 as New Dielectrics for Tunable Components and Dynamic Random Access Memories

Calcium lead titanate ((Pb,Ca)TiO₃) thin films, with calcium contents of ∼50 at.%, have been prepared by chemical solution deposition (CSD). Different synthetic sol–gel methods have been used for the preparation of the precursor solutions. 1,3-propanediol, OH(CH₂)₃OH, and water, H₂O, were used as solvents. Lead (II) acetate trihydrate, Pb(OCOCH₃)₂·3H₂O, and titanium di-isopropoxide bis(acetylacetonate), Ti(OC₃H₇)₂(CH₃COCHCOCH₃)₂, were used as reagents of lead and titanium, respectively. Calcium was incorporated into the solutions as calcium acetate hydrate, Ca(OCOCH₃)₂· x H₂O, or as calcium acetylacetonate hydrate, Ca(CH₃COCHCOCH₃)₂· x H₂O. Only the use of calcium acetate led to precipitate-free solutions. Pb(II)–Ti(IV)–Ca(II) sols were obtained when calcium acetate was refluxed with the lead and titanium reagents in a diol–water solvent. These sols led to films with a homogeneous compositional profile. Solutions obtained by mixing a water solution of calcium acetate with a Pb(II)–Ti(IV) sol led to films with a heterogeneous compositional profile in which an interface between the film and the Pt bottom electrode is formed. The films derived from the Pb(II)–Ti(IV)–Ca(II) sols have values of dielectric constant at room temperature of ∼500, which, together with their low leakage currents, low dielectric losses, and tunability, make these films promising for dynamic random access memories and tunable devices.     

Structural and Electrical Properties of Er2O3-Doped Na1/2Bi1/2TiO3 Lead-Free Piezoceramics

Sodium bismuth titanates Na_1/2Bi_1/2TiO₃ (NBT) doped with 0–3 wt% Er₂O₃ were prepared by the conventional solid-state reaction method. The X-ray diffraction results revealed that the sintered Er-doped NBT ceramics exhibited a pure perovskite structure with Er³⁺ concentrations ranging from 0 to 1 wt%. At a low Er₂O₃ concentration, the Er-doped NBT ceramics showed enhanced electrical properties with dielectric constant ɛ₃₃^T/ɛ₀=636, a low dielectric dissipation factor (tan δ=3.3%), a low coercive field ( E _c=4.56 kV/mm), and a high piezoelectric constant ( d ₃₃=75 pC/N). The relationship between the composition and properties of Er-doped NBT ceramics has been discussed.     

Dielectric and Piezoelectric Properties of the Morphotropic Phase Boundary Composition in the (0.8−x) Pb(Mg1/3Ta2/3)O3−0.2PbZrO3−xPbTiO3 Ternary System

Morphotropic phase boundary (MPB) compositions separating rhombohedral and tetragonal phases in the (1− x − y )Pb(Mg_1/3Ta_2/3)O₃– y PbZrO₃– x PbTiO₃ (PMT–PZ–PT100 x ) ternary solid solution system were characterized using X-ray diffraction and dielectric, piezoelectric properties. This work focused on compositions with a PZ content fixed at y =0.2, with an MPB composition found to be located at x =0.4. Piezoelectric coefficients and dielectric permittivity were found to be on the order of d ₃₃=580 pC/N and 4100, respectively. Acceptor modification using manganese was found to induce a "hardening" effect in 0.4PMT–0.2PZ–0.4PT, with decreased piezoelectric coefficients d ₃₃ and dielectric loss and increased mechanical quality factor Q . Piezoelectric coefficients d ₃₃, Q values, and dielectric loss were found to be 500 pC/N, 2000, and 0.4%, respectively, for 0.4PMT–0.2PZ–0.4PT with MnO₂ dopant levels around 0.5 wt%. The figure of merit (product of Q and d ₃₃) was found to be on the order of 1 × 10⁶, significantly higher when compared with other hard piezoelectric PZT materials. Specifically, the PMT–PZ–PT materials may be attractive candidates for high-power ultrasonic applications, particularly fine-scale components that require relating high permittivities.