Preparation and piezoelectric properties of potassium sodium niobate glass ceramics

This paper describes the preparation of a piezoelectric glass ceramic material from potassium sodium niobate （Ko.sNa0.sNbO3; KNN） using a novel melting method. The effects of the subsequent heat-treatment on the optical, thermal, electrical, and mechanical properties of the material are carefully examined, and its crystal structure and surface morphol- ogy are characterized respectively by x-ray diffraction and scanning electron microscopy. This new material has a much higher piezoelectric coefficient （163 pC.N-1） than traditional piezoelectric ceramics （131 pC.N-1 ）. On this basis therefore, a strategy for the future study and development of lead-free KNN-based piezoelectric glass ceramics is proposed.

Potassium tantalate niobate crystals:Efficient quadratic electro-optic materials and their laser modulation technology

Electro-optic(EO)crystals are important material for all-solid-state laser technology,which can be used to fabricate various laser modulators,such as EO switches,laser deflectors,and optical waveguide.The improvements in new high-efficiency EO crystal materials have held great significance to the development of laser technology.Potassium tantalate niobate(KTN)is a popular multifunctional crystal because of its remarkable and excellent quadratic EO effect.KTN EO modulation technology offers numerous advantages,such as high efficiency,good stability,a quick response time,and inertia-free characteristics.In this paper,we summarize the research progress of KTN series crystals systemically,including the theoretical exploration on quadratic EO effect,solid-melt crystal growth technique,comprehensive physical characterization,new physical effect and mechanisms exploration,new EO devices development and design.The EO modulation technique based on the Kerr effect of KTN series crystal offers obvious advantages in reducing the drive voltage and device size,which could better meet the developmental needs of future lasers with a wide wavelength,miniaturization,and integration.This may provide theoretical guidance and an experimental basis for the design and development of new EO crystal devices and promote the development of laser technology.

Potassium sodium niobate based lead-free ceramic for high-frequency ultrasound transducer applications

The BiAlO_(3)(BA)and(Bi_(0.5)Na_(0.5))ZrO_(3)(BNZ)are selected to form a solid solution with(K_(0.48)Na_(0.52))NbO_(3) via traditional solid state technique to optimize the electrical performance and temperature stability of KNNbased lead-free ceramics,simultaneously.Here we show that doped BA has a great influence on phase structure,morphologies,and electrical properties.The XRD patterns and dielectric constant versus temperature curves reveal that an increase in the BA content results in a transform of phase structures from a coexistence state of rhombohedral,orthorhombic and tetragonal phases to pseudocubic phase.Owing to the construction of R-O-T phase boundary,optimized performances(T_(C)~336℃,d_(33)~306 pC/N,kp=0.48)are obtained in 0.962(K_(0.48)Na_(0.52))NbO_(3)-0.003BiAlO_(3)-0.035(Bi_(0.5)Na_(0.5))ZrO_(3)(KNN-3)ceramics.Based on the sintered KNN-3 ceramic samples,high-frequency ultrasound imaging transducers are designed and fabricated,which exhibits a high center frequency of 24.5 MHz,a broad -6 dB bandwidth of 97% and a high-sensitivity.Finally,the imaging characteristic of the lead-free transducers is demonstrated via ex vivo imaging of biological tissue structure.As environment friendly materials,the excellent electrical and acoustic performance of developed KNN-based ceramics has great potential for practical applications.

Growth Defects in Cubic KTa_(1-x)Nb_xO_3 Crystal

Potassium tantalate niobate （KTa1-xNbxO3, KTN） crystals with different dimensions and quality situations were grown by Czochralski method. Crystal growth process and morphology properties of KTN are presented in this paper. It was found that some defects, such as bubble, inclusion, crack, dislocation etc., can all appear if the crystal is grown in an improper condition. The character and formation mechanism of such defects in macro growth are discussed. We consider that the CO2, which was not released absolutely during the sintering process and dissolved in the melt, led to bubbles. The composition of the inclusion caused by high pulling and rotation rates is KTN polycrystalline. The crack and dislocation in KTN crystal mainly come from improper temperature field. Etching and high-resolution X-ray diffraction （HRXRD） experiment results indicate that the central area is the defects concentrated.

Characterization and Photocatalytic Activity of KSr_2Nb_5O_(15) with Tungsten Bronze Structure

Tungsten bronze （TB） type potassium strontium niobate KSr2Nb5O15 was prepared by solid-state reaction method, and was characterized by X-ray diffraction （XRD）,scanning electron microscopy （SEM） and UV-vis diffuse spectrum. The photocatalyst shows high photocatalytic activity of photodegrading acid red G. The effects of photocatalyst dosage and initial concentration of acid red G on the photodegradation process were studied. The kinetics of photocatalytic degradation of acid red G by KSr2Nb5O15 catalyst follows the first order reaction.

KLN单晶的SHG特性

Tetragonal tungsten bronze structure potassium lithium niobate (KLN) crystals pr omise as a potentially useful material for nonlinear optical applications,especi ally,for blue laser radiation by second harmonic generation (SHG).We have grown KLN single crystals by TSSG method using different melt compositions and studied the properties of second harmonic generation (SHG).The crystals have the conten ts of Nb 2O 5 in the range of 51 54% and Li 2O in the range of 17.5 20% and a non critical SHG phase matching wavelength being a wide range from 843 and 9 67 nm. The dependence of temperature and SHG phase match wavelength and the temp erature acceptance were measured by a cw Ti∶Al 2O 3 laser(Spectra Physics M odel 3900S).The results show a linear relationship between phase match wavelengt h and temperature and a about 4℃ temperature acceptance.The homogeneity on a KL N crystal sample of 4×5×8mm was characterized where the SHG phase match wavele ngth changed within 887.8 and 887.5nm . With comparing the wavelength accepta nce being 0.5nm,the result suggests that the homogeneity is good. The dependence bet ween crystal composition,crystal lattice constants and SHG properties will be di scussed.

KLN晶体生长与蓝光SHG特性

In this paper,ferroelectric tetragonal tungsten bronze type potassium lithium niobate(KLN)crystal with a size of 20mm×8mm×43mm was grown from a melt with a composition of 32mol% K 2CO 3,24mol% Li 2CO 3 and 44mol% Nb 2O 5 by the top seeded solution growth (TSSG)method.The KLN crystal as grown along [110]axis has a perfect crystal melt interface dominated by {110} and {210} facets.Lattice constants were measured by X ray diffraction (XRD) analysis performed on {001}and {110}natural faces of single crystal samples.The anisotropic thermal expansion behavior of the crystal was also studied along [001] and [110] axes,respectively by using a Shimadzu TMA 50 thermomechnical analyzer.For the purpose of crystal poling,the dependence of crystal capacitance vs.temperature in both heating and cooling cycles was measured and the ferroelectric Curie temperature was determined to be 514℃.The crystal was poled at 506℃ with a dc field of about 250 V/cm along the c axis of the sample,for a time corresponding to about 1.5 h/cm.The blue second harmonic generation (SHG)characteristics of the KLN crystal were investigated by using a 3900s Ti∶sapphire CW tunable laser.Blue laser light at wavelength 432nm was obtained by the non critical phase matching (NCPM)SHG at room temperature.Based on the wavelength and temperature tuning curves for the NCPM SHG,the wavelength acceptance and temperature acceptance of this KLN crystal were measured.The crystal property homogeneity along the <110>growth axis was also studied by measuring the room temperature NCPM wavelength at different growth positions.

Growth and Raman Study of Phase Transitions of the KTa0.63Nb0.37O3 Crystal

The potassium tantalate niobate KTa_（0.63）Nb_（0.37）O_3 single crystal with large size and good quality was synthesized by Czochralski method.The crystal composition and structure were determined by electric probe microanalysis（EPMA） and X-ray diffraction（XRD） technique,respectively.The sequence of phase transitions of the as-grown crystal was investigated by Raman scattering technique.What features in the phonon spectrum corresponding to each phase transition,namely cubic to tetragonal（C-T）,tetragonal to orthorhombic（T-R） and orthorhombic to rhombohedral（O-R）,is discussed.Following the features the C-T phase transition point measured is in the vicinity of –40 ℃,and the difference from theoretical value was discussed;T-O phase transition point is at around –130 ℃,while the O-R phase transition point was not obtained due to the band overlapping and experiment limit.

Photocatalytic Degradation of Metronidazole in Aqueous Solution by Niobate K_6Nb_(10.8)O_(30)

The photocatalytic degradation of antibiotic metroni-dazole in aqueous solution by niobate K6Nb10.8O30 photocatalyst that was prepared using a soft-chemical method was studied by Fourier transform infrared spectroscopy and UV-Vis absorption spectrum. Metronidazole is very stable and is difficult to degrade under UV irradiation. K6Nb10.8O30 photocatalyst cannot degrade metronidazole without UV irradiation and shows very high photo-catalytic activity for the degradation of metronidazole under UV irradiation. The photocatalytic degradation rate of metronidazole increased with increasing the dosage of K6Nb10.8O30 photocatalyst. The photocatalytic degradation reaction of metronidazole by nio-bate K6Nb10.8O30 follows the first-order kinetic equation.

Optimizing energy harvesting performance by tailoring ferroelectric/relaxor behavior in KNN-based piezoceramics

Piezoelectric energy harvesters(PEHs)fabricated using piezoceramics could convert directly the mechanical vibration energy in the environment into electrical energy.The high piezoelectric charge coefficient(d_(33))and large piezoelectric voltage coefficient(g_(33))are key factors for the high-performance PEHs.However,high d_(33)and large g_(33)are difficult to simultaneously achieve with respect to g_(33)=d_(33)/(e_(0)e_(r))and d_(33)=2Qe_(0)e_(r)P_(r).Herein,the energy harvesting performance is optimized by tailoring the CaZrO_(3)content in(0.964−x)(K_(0.52)Na_(0.48))(Nb_(0.96)Sb_(0.04))O_(3)-0.036(Bi_(0.5)Na_(0.5))ZrO_(3)-xCaZrO_(3)ceramics.First,the doping CaZrO_(3)could enhance the dielectric relaxation due to the compositional fluctuation and structural disordering,and thus reduce the domain size to~30 nm for x=0.006 sample.The nanodomains switch easily to external electric field,resulting in large polarization.Second,the rhombohedral-orthorhombic-tetragonal phases coexist in x=0.006 sample,which reduces the polarization anisotropy and thus improves the piezoelectric properties.The multiphase coexistence structures and miniaturized domains contribute to the excellent piezoelectric properties of d_(33)(354 pC/N).Furthermore,the dielectric relative permittivity(ε_(r))reduces monotonously as the CaZrO_(3)content increases due to the relatively low ion polarizability of Ca^(2+)and Zr^(4+).As a result,the optimized energy conversion coefficient(d_(33)×g_(33),5508×10^(−15)m^(2)/N)is achieved for x=0.006 sample.Most importantly,the assembled PEH with the optimal specimen shows the excellent output power(~48 mW)and lights up 45 red commercial light-emitting diodes(LEDs).This work demonstrates that tailoring ferroelectric/relaxor behavior in(K,Na)NbO_(3)-based piezoelectric ceramics could effectively enhance the electrical output of PEHs.

Multi-phase structure and electrical properties of Bi_(0.5)Li_(0.5)ZrO_3 doping K_(0.48)Na_(0.56)NbO_3 lead-free piezoelectric ceramics

(1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3(KNN–x BLZ, x = 0–0.06) lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method, and their phase structures and electric properties as well as T_C were systematically investigated. The orthorhombic–tetragonal(O–T) two phases were detected in all(1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3 ceramics at 0.01 ≤ x ≤ 0.05. Due to the appropriate ratio between O phase and T phase(CO/C T= 45/55), high piezoelectric properties of d 33= 239 pC/N, k_p= 34%, and P_r = 25.23 μC/cm^2 were obtained at x = 0.04. Moreover, a high T_C = 348 ℃ was also achieved in KNN–x BLZ ceramic at x = 0.04. These results indicate that (1–x)K_(0.48)Na_(0.56)NbO_3–xBi_(0.5)Li_(0.5)ZrO_3 system is a promising candidate for high-temperature piezoelectric devices.

A REVIEW ON LEAD-FREE PIEZOELECTRIC CERAMICS STUDIES IN CHINA

There are a large number of research publications on the hot topic of environmental friendly leadfree piezoelectric materials worldwide in the last decade.The number of researchers and institutions involved from China is much larger than other countries or regions.The publications by Chinese researchers cover a broad spectrum on the preparations,structures,properties and applications of lead-free piezoelectric ceramics.This has motivated us to come out with a review on recent advances in development of lead-free piezoelectric ceramics in China.The emphases are especially on the preparation and electric properties of barium titanate-based materials,bismuth sodium titanate and related materials,alkaline niobate and related materials,bismuth layerstructured materials,as well as texture engineering of ceramics and some of their single crystals.Hopefully,this could give further impetus to the researchers to continue their e®orts in this promising area and also draw the attentions from legislature,research o±ce,industrial and publics.

Electrical properties and luminescence properties of 0.96(K0.48Na0.52)(Nb0.95Sb0.05)–0.04Bi0.5(Na0.82K0.18)0.5ZrO3–xSm lead-free ceramics

In this paper,Sm-doped 0.96(K0.48 Na0.52)(Nb0.95 Sb0.05)–0.04 Bi0.5(Na0.82 K0.18)0.5 Zr O3(abbreviated as KNSN–0.04 BNKZ)lead-free piezoelectric ceramics were prepared by conventional solid-state sintering method and the effects of Sm2 O3 on the phase structure,microstructure,electrical and luminescent properties of KNSN–0.04 BNKZ potteries were studied.Results revealed that a single solid solution phase with pseudo-cubic perovskite structure was formed between KNSN–0.04 BNKZ and Sm2 O3.Existence of weak dielectric/ferroelectric properties with a diffuse dielectric anomaly and slim P–E hysteresis loops of the Sm-doped KNSN–0.04 BNKZ demonstrated the ferroelectric relaxor behavior of the KNNS–0.04 BNKZ–x Sm ceramics.Accordingly,the temperature stability and fatigue behavior of the modified ceramics were significantly improved.It was found that the KNSN–0.04 BNKZ ceramics with 0.002 mol Sm addition exhibited nearly temperature independent properties and fatigue-free behavior.Moreover,Sm-modified KNSN–0.04 BNKZ exhibits a bright photoluminescence with a strong orange emission under visible light irradiation.As a material with both electrical and luminescent properties,it has good application prospect in future optoelectronic components by integrating its luminescent and electrical properties.

Effects of Ge4＋ acceptor dopant on sintering and electrical properties of （K0.5Na0.5）NbO3 lead-free piezoceramics

Lead-free （K0.5Na0.5）（Nb1-xGex）O3 （KNN-xGe, where x = 0-0.01） piezo- electric ceramics were prepared by conventional ceramic processing. The effects of Ge4＋cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge4＋ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge4＋ cations substituted Nbs＋ ions as acceptors, and the Curie temperature （Tc） shows an almost linear decrease with increasing the Ge4＋ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020℃. Ge4＋ doping less than 0.4 mol.% can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties： piezoelectric constant d33 = 120 pC/N, planar electromechanical coupling coefficient kp = 34.7%, mechanical quality factor Qm = 130, and tanδ = 3.6%.

Improvement in synthesis of （K0.5Na0.5）NbO3 powders by Ge4＋ acceptor doping

In this paper, the effects of doping with GeO2 on the synthesis temperature, phase structure and morphology of （K0.5Na0.5）NbO3 （KNN） ceramic powders were studied using XRD and SEM. The results show that KNN powders with good crystallinity and compositional homogeneity can be obtained after calcination at up to 900℃ for 2 h. Introducing 0.5 mol.% GeO2 into the starting mixture improved the synthesis of the KNN powders and allowed the calcination temperature to be decreased to 800℃, which can be ascribed to the formation of the liquid phase during the synthesis.

BiCoO3-doped （Ko.47sN ao.47sLio.os）（N bo.8Tao.2）03 lead-free piezoelectric ceramics

（1-x）（K0.47sNa0.475Li0.os）（Nb0.sTa0.2）O3-xBiCoO3 （KNLNT-BC） lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method. Effects of the BC content on the phase structure, microstructure and electrical properties of KNLNT-BC ceramics were investigated. XRD patterns reveal that all the ceramic samples are in the pure perovskite-type structure, and the phase structure changes from the tetragonal to pseudo-cubic phase with the increase of the BC content. After the substitution of BC, the grain size is significantly reduced and relaxer behaviors are induced. By adding a small amount of BC to KNLNT ceramics, piezoelectric properties are improved, while further addition of BC makes the piezoelectric properties deteriorate markedly. The optimized electrical properties atx= 0.005 are as follows： d33 = 194 pC/N, kp = 0.44.

Exceptional electrostrain with minimal hysteresis and superior temperature stability under low electric field in KNN-based lead-free piezoceramics

Over the past two decades,(K_(0.5)Na_(0.5))NbO_(3)(KNN)-based lead-free piezoelectric ceramics have made significant progress.However,attaining a high electrostrain with remarkable temperature stability and minimal hysteresis under low electric fields has remained a significant challenge.To address this long-standing issue,we have employed a collaborative approach that combines defect engineering,phase engineering,and relaxation engineering.The LKNNS-6BZH ceramic,when sintered at T_(sint)=1170℃,demonstrates an impressive electrostrain with a d_(33) value of 0.276%and 1379 pm·V^(-1)under 20 kV·cm^(-1),which is comparable to or even surpasses that of other lead-free and Pb(Zr,Ti)O_(3)ceramics.Importantly,the electrostrain performance of this ceramic remains stable up to a temperature of 125℃,with the lowest hysteresis observed at 9.73%under 40 kV·cm^(-1).These excellent overall performances are attributed to the presence of defect dipoles involving V′_(A)-V∙∙_(O) and B′_(Nb)-V∙∙O,the coexistence of R-O-T multiphase,and the tuning of the trade-off between long-range ordering and local heterogeneity.This work provides a lead-free alternative for piezoelectric actuators and a paradigm for designing piezoelectric materials with outstanding comprehensive performance under low electric fields.