Alkali Niobate Research Articles

Microwave-assisted alkaline fusion followed by water-leaching for the selective extraction of the refractory metals tungsten, niobium and tantalum from low-grade ores and tailings

The refractory metals tungsten, tantalum and niobium are considered critical raw materials in Europe. Diversifying the supply of such materials, for instance by recovering refractory metals from local low-grade ore materials could reduce their supply risks. However, the extraction processes require to be efficient with a low energy and material consumption and a minimal environmental impact. In this work, microwave (MW) assisted alkaline fusion was explored to extract tungsten from scheelite containing ore materials with different grades (high to very low) and tantalum and niobium from a columbite-tantalite [(Fe,Mn)(Nb,Ta)2O6] concentrate. During the fusion process scheelite was converted into soluble alkali tungstate salts [Na2WO4, K2WO4 and/or K3Na(WO4)2] and the reaction temperature could be lowered to 150–200 °C by fusion with a low-melting eutectic alkali salt system of an 1:1 (m/m) NaOH:KOH mixture. The application of MW-assisted heating allowed for fast and volumetric heating, thereby lowering reaction times to 10 min – 30 min. After fusion, tungsten was extracted by a simple water leaching step leading to extraction efficiencies ranging from 77 % to 97 %. Noteworthily, also P, S and As, which all form soluble oxyanions were extracted from the studied materials. Extraction of niobium and tantalum was also achieved though MW-assisted alkaline fusion as an alternative to acidic fluorine-based hydrometallurgical processes. MW-assisted heating allowed for a fast conversion of the (Fe,Mn)(Nb,Ta)2O6 into alkali tantalate and niobate salts. Under optimal conditions, MW-assisted fusion with KOH (salt:sample = 3:1 (m/m)) at 400 °C for 10 min leached ca. 74 %–88 % of tantalum and 77 %–86 % of niobium into water (L/S=10) at 40 °C for 120 min, while the main matrix elements Mn and Fe displayed limited dissolution (<4%). Due to the low solubility of sodium tantalate and niobate salts in water, MW-assisted alkaline fusion in an eutectic NaOH:KOH mixture followed by water leaching was not efficient.

Facile preparation of KNN thin film with high purity phase and excellent electrical properties

Obtaining high purity alkali niobate (K x Na1-x NbO3) thin films without secondary phase on metal coated traditional silicon (Si) substrates via sol–gel technique has remained great challenges until now. Herein, we report K0.5Na0.5NbO3 (KNN) thin films successfully deposited on Pt/Ti/SiO2/Si(100) substrates by a simply effective sol–gel process. A comprehensive and systematic investigation of processing conditions on the microstructures and electrical properties of spin-coated KNN films was presented. We have found that phase purity and microstructures of KNN films are strongly influenced by content of alkali excess and the annealing temperature. Thin films with an equal excess amount of 10% mol K and Na (KNN1) sintered at 650 °C show high crystallinity with a preferred (100)-orientation degree of 78%, and homogeneous and dense surface with columnar structure and large grain size up to 254 nm. The result of quantitative XPS analysis has proved that the composition of the film is close to the chemical stoichiometry. As a consequence, the obtained KNN1 films exhibit a large dielectric constant of 775 and low dielectric loss of ∼2% in the wide frequency range from 1kHz up to 10MHz as well as the best shape of P−E loops. Furthermore, leakage current density of the film is about 9.45 × 10−5 A cm−2 at E ≈100 kV cm−1.

Effect of Local Structural Distortions on Antiferroelectric-Ferroelectric Phase Transition in Dilute Solid Solutions of KxNa1-xNbO3.

The fundamental principles that govern antiferroelectric (AFE)-ferroelectric (FE) transitions are not well understood for many solid solutions of perovskite compounds. For example, crystal chemical considerations based on the average Goldschmidt tolerance factor or ionic polarizability do not precisely predict the boundary between the AFE and FE phases in dilute solid solutions of alkali niobates, such as KxNa1-xNbO3 (x ≤ 0.02). Here, based on detailed structural analysis from neutron total scattering experiments, we provide insights about how the relative local distortions around the A- and B-sites of the ABO3 perovskite structure affect the AFE/FE order of the average crystallographic phases in KxNa1-xNbO3. We show that a higher (lower) ratio of B-site-centered distortions over A-site-centered distortions drives transition toward a long-range FE (AFE) phase, which is based on a competition between the long-range polarizing field of the Nb-O dipoles and the disordering effect of local distortions around the A-site. Our study provides a predictive tool for designing complex solid-solution perovskites with tunable (anti)ferroelectric polarization properties, which can be of interest for various energy-related applications such as high-density energy storage and solid-state cooling.

Diverse Defects in Alkali Niobate Thin Films: Understanding at Atomic Scales and Their Implications on Properties.

Defects in ferroelectric materials have many implications on the material properties which, in most cases, are detrimental. However, engineering these defects can also create opportunities for property enhancement as well as for tailoring novel functionalities. To purposely manipulate these defects, a thorough knowledge of their spatial atomic arrangement, as well as elastic and electrostatic interactions with the surrounding lattice, is highly crucial. In this work, analytical scanning transmission electron microscopy (STEM) is used to reveal a diverse range of multidimensional crystalline defects (point, line, planar, and secondary phase) in (K,Na)NbO3 (KNN) ferroelectric thin films. The atomic-scale analyses of the defect-lattice interactions suggest strong elastic and electrostatic couplings which vary among the individual defects and correspondingly affect the electric polarization. In particular, the observed polarization orientations are correlated with lattice relaxations as well as strain gradients and can strongly impact the properties of the ferroelectric films. The knowledge and understanding obtained in this study open a new avenue for the improvement of properties as well as the discovery of defect-based functionalities in alkali niobate thin films.

Achieving power-dependent fluorescence intensity ratio via enhanced photothermal effect in rare-earth and CaCu3TiO12 co-doped alkali niobate ceramics

Controlling the laser power density is one of the major means to bring photothermal conversion phenomenon. However, only a slight temperature enhancement was achieved by exposure to the laser. How to enhance photothermal conversion to develop power-sensitive fluorescence intensity ratio technology becomes a problem. Here, we report an eco-friendly niobate-based ceramic (K 0.25 Na 0.25 NbO 3 ) doped with rare earth ions (Er 3+ , Yb 3+ ) and simultaneously modified with CaCu 3 TiO 4 , exhibiting superior photothermal effect (PTE) and fluorescence intensity ratio (FIR). Thereinto, PTE originating from the up-conversion luminescence of Er 3+ greatly elevates due to the Cu 2+ quenching and Yb 3+ sensitization. Meanwhile, the defects formed by the volatilization of potassium and sodium at high temperature can enhance PTE (70 °C, 0.4 W) and power sensitivity ( S p = 0.61 W -1 ). Under multiple power cycles, stable FIR of the ceramic shows outstanding resistance to temperature in long-term power-dependent tests. Furthermore, this strategy can open opportunities for preparing efficient photothermal conversion ceramics and exploiting PTE for vision-to-tactile sensory conversion.

Negative Capacitance Phenomenon and Origin in Alkali Niobate Film with Self‐Assembled Lattice Faults

AbstractNegative capacitance (NC) is an important phenomenon both in terms of the underlying fundamental science and its potential device application value. Achieving NC with adequate tunability in a scalable and reliable way is highly demanded for industrial applications. Herein, an electric‐field‐induced NC phenomenon and inductance‐like behavior in alkali‐deficient potassium sodium niobate thin film with self‐assembled planar faults are demonstrated. Our in‐depth investigation with the help of atomic‐scale microscopy and high‐temperature dielectric, conductivity, and X‐ray studies revealed that the compensated electronic charge at the planar faults is localized as bound polarons which convert to free polarons at high temperature as well as by an increased electric field. The collective response of such polaronic charge along the planar faults under an oscillating electric field results in the observed NC phenomenon and inductance effect. Large NC values are obtained which can be tuned in terms of magnitude and operating frequency by controlling the concentration of the free polarons via external DC bias. This work underpins the unique feature of the defect architecture obtained in the alkali deficient KNN film and provides a novel material design strategy and fundamental framework to realize NC and related exotic phenomena in defect‐engineered oxide materials.

Origin of giant electric-field-induced strain in faulted alkali niobate films

A large electromechanical response in ferroelectrics is highly desirable for developing high-performance sensors and actuators. Enhanced electromechanical coupling in ferroelectrics is usually obtained at morphotropic phase boundaries requiring stoichiometric control of complex compositions. Recently it was shown that giant piezoelectricity can be obtained in films with nanopillar structures. Here, we elucidate its origin in terms of atomic structure and demonstrate a different system with a greatly enhanced response. This is in non-stoichiometric potassium sodium niobate epitaxial thin films with a high density of self-assembled planar faults. A giant piezoelectric coefficient of ∼1900 picometer per volt is demonstrated at 1 kHz, which is almost double the highest ever reported effective piezoelectric response in any existing thin films. The large oxygen octahedral distortions and the coupling between the structural distortion and polarization orientation mediated by charge redistribution at the planar faults enable the giant electric-field-induced strain. Our findings demonstrate an important mechanism for realizing the unprecedentedly giant electromechanical coupling and can be extended to many other material functions by engineering lattice faults in non-stoichiometric compositions.

Synthesis of KNN nanoblocks through surfactant-assisted hot injection method and fabrication of flexible piezoelectric nanogenerator based on KNN-PVDF nanocomposite

With the tremendous growth of flexible piezoelectric nanogenerators, alkali niobates have gained considerable attention and are perceived to be the eco-friendly substitute for the unsustainable lead based piezoelectric systems. However, successful realization of potassium sodium niobate (KNN) based devices with appreciable piezoelectricity requires tailored molecular level organization. Herein, we have developed a lead-free flexible piezoelectric nanogenerator based on KNN-PVDF nanocomposite, in which the KNN nanoblocks were synthesized using a novel non-aqueous surfactant-assisted hot injection method. Also, the synthesis of KNN employed non-toxic surface stabilizer, oleic acid and reaction catalyst, oleyl amine respectively, making the preparation environmental benign. The KNN nanoblocks homogeneously dispersed in the PVDF matrix up to 10 wt% filler loading, enhanced the piezoelectric and dielectric properties of the composite. Further, the fabricated flexible piezoelectric nanogenerator without any external poling process exhibits an output open circuit voltage of ∼ 2.1 V and a short circuit current of ~ 42 nA on a gentle finger tapping force (~3 N). The results demonstrate the potential of chemically engineered KNN nanoblocks dispersed in PVDF for large-scale sustainable piezoelectric nanogenerator applications.

Ferroelectric domain formation and photocatalytic activity on porous alkali niobate piezoelectric ceramics

Present study showed synthesis of novel type of porous alkali niobate piezoelectric ceramics, and the formation of domains and photocatalytic activity for the porous piezoelectric ceramics were investigated while comparing with dense ceramics to confirm enhancement of domain orientation and photocatalytic activity around pores. Porous Li0.06Na0.47K0.47NbO3 piezoelectric ceramics were synthesized by a template method using polymethylmethacrylate as a pore former agent. Uniform pores with 6 µm in diameter were dispersed in the porous ceramics. Porous ceramics synthesized with 10 vol % of the pore former agent showed piezoelectric voltage coefficient, 29 mVm/N, which is same as that of the dense ceramics. Smaller striped domains formed at an edge of pores on the porous ceramics, indicating that orientation of domains was promoted by electric field concentration around the pores. Through photoreduction reaction of Ag+ ion, local precipitation of Ag was shown around the pores on the poled porous ceramics, whereas Ag was located over an entire surface of unpoled porous ceramics. Highest photocatalytic activity was shown for the poled porous ceramics in photodecomposition test of methylene blue. These results clearly indicated photocatalytic activity was enhanced on ferroelectric domains around pores of porous piezoelectric ceramics.

Alkali-deficiency driven charged out-of-phase boundaries for giant electromechanical response

Traditional strategies for improving piezoelectric properties have focused on phase boundary engineering through complex chemical alloying and phase control. Although they have been successfully employed in bulk materials, they have not been effective in thin films due to the severe deterioration in epitaxy, which is critical to film properties. Contending with the opposing effects of alloying and epitaxy in thin films has been a long-standing issue. Herein we demonstrate a new strategy in alkali niobate epitaxial films, utilizing alkali vacancies without alloying to form nanopillars enclosed with out-of-phase boundaries that can give rise to a giant electromechanical response. Both atomically resolved polarization mapping and phase field simulations show that the boundaries are strained and charged, manifesting as head-head and tail-tail polarization bound charges. Such charged boundaries produce a giant local depolarization field, which facilitates a steady polarization rotation between the matrix and nanopillars. The local elastic strain and charge manipulation at out-of-phase boundaries, demonstrated here, can be used as an effective pathway to obtain large electromechanical response with good temperature stability in similar perovskite oxides.

Growth and characterization of large size lead‐free ferroelectric K(Ta,Nb)O3 single crystal

AbstractLead‐free piezoelectric materials with excellent performance are greatly demanded for the environmental issues. The lead‐free ferroelectric single crystals are therefore greatly concerned for their much higher piezoelectricity than the polycrystalline counterparts and the domain‐tunable property. However, the growth of large size and high‐quality lead‐free ferroelectric crystals has always been a great challenge. In this work, a ferroelectric KTa1‐xNbxO3 (KTN) single crystal with an extremely large size of 25 × 25 × 37 mm3 was grown using the modified top‐seeded solution growth method. The large size enabled us to carry out comprehensive investigations on the crystal. The complete sets of dielectric, piezoelectric, and elastic constants for the [001]C‐poled KTN crystal with quasi single domain state were determined. Results showed that the crystal exhibits high electromechanical coupling coefficients with kt~0.642 and k33~0.679. Furthermore, the orientation dependence of the piezoelectric, dielectric, and elastic properties was determined by the tensor matrix transformation technique, and the maximum d33, , and k33 were found along the polar direction [001]C. This work not only provides important guidance for the growth technology of lead‐free ferroelectric crystals but also offers essential datasets of lead‐free alkali niobate system, which is of great importance for both theoretical studies and designs of electromechanical devices.

Novel lead-free composites with two porosity levels: large piezoelectric anisotropy and high sensitivity

A novel lead-free 1–3-type composite based on a ferroelectric domain-engineered single crystal is put forward. In the porous polymer matrix of this composite, two different porous structures are observed, and the effect of these structures on the piezoelectric performance, electromechanical coupling and related anisotropy parameters of 1–3-type composites is first studied. New diagrams that link the volume fractions of the single-crystal component and the porous regions in the polymer medium are built to show validity of conditions for a large anisotropy of piezoelectric coefficients and electromechanical coupling factors , and . In the composites based on the complex alkali niobate alkali tantalate single crystal with small piezoelectric anisotropy (/|| = 2.1), the three anisotropy factors /|| ≥ 5, /|| ≥ 5 and /|| ≥ 5 hold simultaneously due to the presence of layers with heavily prolate and heavily oblate air pores in the porous polymer matrix. The two porosity levels influence the elastic anisotropy of the porous matrix, and this leads to an increase in the three anisotropy factors across wide volume-fraction ranges. Of independent interest is the high piezoelectric sensitivity of the composites for which the condition ≥1 V m N−1 holds at their piezoelectric coefficient ≈ (200–500) pC N−1 and electromechanical coupling factors ≈ ≈ 0.8–0.9. The studied parameters of the novel piezo-active 1–3-type composites are of value for various applications such as active elements of piezoelectric transducers, energy-harvesting devices and sensors.

Cycling‐ and heating‐induced evolution of piezoelectric and ferroelectric properties of CuO‐doped K0.5Na0.5NbO3 ceramic

AbstractFor accepter‐doped perovskite piezoelectric ceramics, macroscopic properties of the materials (eg, hardening, fatigue, and aging) are closely related to microscopic characteristics (eg, oxygen vacancies and defect dipoles). In this work, the relationship of macroscopic and microscopic characteristics in CuO‐doped K0.5Na0.5NbO3 (KNN) ceramic has been studied by subjecting the material to electric field cycling, quenching, heating, and consequently aging. The introduction of CuO in KNN generates and . The defect dipoles exhibit obviously the pinning effect on ferroelectric domains and thus induce a completely pinched/double P‐E loop and excellent hardening piezoelectricity of high Qm of 2235. With the destruction of short‐range symmetry uniformity between defect dipoles and ferroelectric dipoles induced by electric field cycling, quenching and heating, the ceramic can be depinned and softened. As a result, the depinned ceramic possesses an opened single ferroelectric hysteresis loop and the significantly decreasing Qm. A distinctive aging is observed in the depinned ceramic. This study provides deep insights into the evolution of electrical properties of accepter‐modified alkali niobate perovskite ceramics under electric field cycling, quenching, and heating.

Temperature dependent dielectric relaxation and ac–conductivity of alkali niobate ceramics studied by impedance spectroscopy

Sodium niobate (NaNbO3) ceramics is prepared by conventional solid state reaction method at sintering temperature 1150 °C for 4 h. The structural information of the material has been investigated by X-ray diffraction (XRD) and Field emission scanning electron microscopy (FE-SEM). The XRD analysis of NaNbO3 ceramics shows an orthorhombic structure. The FE-SEM micrograph of NaNbO3 ceramics exhibit grains with grain sizes ranging between 1 µm to 5 µm. The surface coverage and average grain size of NaNbO3 ceramics are found to be 97.6 % and 2.5 µm, respectively. Frequency dependent electrical properties of NaNbO3 is investigated from room temperature to 500 °C in wide frequency range (100 Hz–5 MHz). Dielectric constant, ac–conductivity, impedance, modulus and Nyquist analysis are performed. The observed dielectric constant (1 kHz) at transition temperature (400 °C) are 975. From conductivity analysis, the estimated activation energy of NaNbO3 ceramics is 0.58 eV at 10 kHz. The result of Nyquist plot shows that the electrical behavior of NaNbO3 ceramics is contributed by grain and grain boundary responses. The impedance and modulus spectrum asserts that the negative temperature coefficient of resistance (NTCR) behavior and non-Debye type relaxation in NaNbO3.

Fabrication and Photocatalytic Applications of Perovskite Materials with Special Emphasis on Alkali-Metal-Based Niobates and Tantalates

Population explosion has caused serious environmental and energy-related problems that have increased the interest of researchers to develop new nontoxic, inexpensive, stable, and efficient materials to address these environment and energy-related issues. Among the different efforts, the development of photocatalysts is considered as an important way to utilize the sustainable solar energy for environment remediation and energy purposes. Presently, several hundred photocatalysts have been synthesized. Among them, alkali niobates and tantalates represent an important class of photocatalysts, because of their nontoxicity, structural flexibility, and simplicity. This review summarizes recent developments in synthetic strategies of alkali niobate and tantalates, their important application as photocatalysts for environment remediation and energy applications, and efforts being made to modify their physicochemical properties and extend their efficiencies by tuning different reaction conditions. The purpose of ...

Novel rhombohedral and tetragonal phase boundary with high T C in alkali niobate ceramics

We design a new composition to establish rhombohedral and tetragonal phase coexistence in alkali niobate ceramics. The composition of (1−x)[0.94(K0.48Na0.52)NbO3–0.045Bi0.5Na0.5ZrO3−0.015CaTiO3]–xLi0.2Na0.8NbO3 has been synthesized by conventional solid-state reaction method. XRD patterns and curves of permittivity versus temperature show that the phase of this kind of perovskite structure ceramics convert tetragonal phase (x ≤ 0.4) into rhombohedral phase (x ≥ 0.5), and the rhombohedral and tetragonal (R-T) phases coexistence has been confirmed at x = 0.425 ~ 0.475. Around this phase boundary, the ceramics with x = 0.425 show an optimum piezoelectric properties (d 33 ~ 178 pC/N and k p ~ 38.5%) with high T C ~ 400 °C. Moreover, the ceramics exhibited strong temperature stability. This work exhibits obviously different piezoelectric properties from other R-T coexistence systems in KNN-based ceramics, the underlying physical mechanism has been discussed. It is believed that this method could promote the further development of alkali niobate ceramics.

Synthesis of ferroelectric K1-xNaxNb1-yTayO3 nanoparticles using a supercritical water flow system

Ta doped alkali niobate, K1-xNaxNb1-yTayO3 (KNNT) nanoparticles (ca. 60–80nm) were continuously synthesized from Nb/Ta-sol with polyacrylic acid as a dispersant and NaOH/KOH solutions using a supercritical water flow system. The syntheses were carried out at temperatures from 400 to 480°C, at pressures from 25 to 30MPa, and at reaction times from 0.5 to 8s. Single phase KNNT was obtained at 480°C and 25MPa for which the Na/(Na+K) and Ta/(Ta+Nb) molar ratios of the products increased with an increase in the precursor molar ratios with slopes of 2.7 and 1.0 for Na/(Na+K) and Ta/(Ta+Nb), respectively. Single phase K0.5Na0.5Nb0.7Ta0.3O3 was obtained from the precursor composition with initial Na/(Na+K) and Ta/(Ta+Nb) molar ratios of 0.19 and 0.3, respectively. Crystallinity increased with an increase in the reaction time and the particles formed at 0.5s were spherical-shaped and they were cube-shaped at the longer reaction times. Single KNNT phase was predominantly produced at high temperatures (ca. 420–480°C) and moderate pressures (ca. 25–30MPa), and was formed at 420°C, 25MPa where the density of water was less than 150kgm−3. The ferroelectric property of KNNT particles sintered at 1085°C was determined to be 96.0pC/N.

Composition dependence of phase boundary and electrical properties in lead-free (K0.5Na0.5)(Nb0.96Sb0.04)O3–Bi0.5Na0.5ZrO3–Bi0.5Li0.5ZrO3 ceramics

In this work, (K0.5Na0.5)(Nb0.96Sb0.04)O3–Bi0.5Na0.5ZrO3–Bi0.5Li0.5ZrO3 lead-free ceramics were fabricated by the conventional solid-state method, and effects of Bi0.5Li0.5ZrO3 on their phase structure and electrical properties were studied. Their piezoelectric properties are sensitive to the addition of Bi0.5Li0.5ZrO3 as well as its contents. The addition of Bi0.5Li0.5ZrO3 simultaneously increased their Curie temperature and decreased rhombohedral and tetragonal phase transition temperature. Their dielectric, ferroelectric, and piezoelectric properties were strongly dependent on Bi0.5Li0.5ZrO3 contents. With increasing Bi0.5Li0.5ZrO3 contents, their dielectric loss can be decreased, and their k p and P r values can be further optimized. However, their e r and d 33 slightly decreased with the increase of Bi0.5Li0.5ZrO3 contents due to the deviation of rhombohedral and tetragonal phase boundary, and the ceramics with x ≤ 0.2 exhibited a high d 33 of >410 pC/N. As a result, this work could further understand the role of Bi0.5Li0.5ZrO3 in electrical properties of high-performance alkali niobate ceramics.

Giant Piezoelectricity and High Curie Temperature in Nanostructured Alkali Niobate Lead-Free Piezoceramics through Phase Coexistence.

Because of growing environmental concerns, the development of lead-free piezoelectric materials with enhanced properties has become of great interest. Here, we report a giant piezoelectric coefficient (d33) of 550 pC/N and a high Curie temperature (TC) of 237 °C in (1-x-y)K1-wNawNb1-zSbzO3-xBiFeO3-yBi0.5Na0.5ZrO3 (KNwNSz-xBF-yBNZ) ceramics by optimizing x, y, z, and w. Atomic-resolution polarization mapping by Z-contrast imaging reveals the intimate coexistence of rhombohedral (R) and tetragonal (T) phases inside nanodomains, that is, a structural origin for the R-T phase boundary in the present KNN system. Hence, the physical origin of high piezoelectric performance can be attributed to a nearly vanishing polarization anisotropy and thus low domain wall energy, facilitating easy polarization rotation between different states under an external field.

Low-temperature sintering and enhanced dielectric properties of alkali niobate ceramics prepared from solvothermally synthesized nanopowders

Sodium niobate nanopowders (N-NaNbO3) and submicron powders (M-NaNbO3) were synthesized by the solvothermal and hydrothermal route, respectively. Subsequently, their sintering activities were comparably investigated through a modified solid-state sintering process. It's found that N-NaNbO3 green bodies presented an apparent shrinkage after the calcination at 650°C, and dense N-NaNbO3 ceramics can be obtained at 950°C. Besides, the optimized sintering temperature of N-NaNbO3 ceramics was 100°C lower, yet the shrinkage was four times larger when compared with M-NaNbO3 samples. Importantly, N-NaNbO3 samples showed improved dielectric properties in the whole frequency range, and the room temperature relative dielectric constant (εr) of N-NaNbO3 samples sintered at 950°C was as high as ~8000. The improved permittivity of N-NaNbO3 samples was attributed to the compact microstructure, unique crystalline structure and less oxygen vacancies. At the same time, the effect of abnormal phase transition behavior originated from the metastable structure was considered to explain the enhanced room temperature permittivity. It's believed that the solvothermal route has great potentials in the synthesis of alkali niobate ceramics powders with high activity for low-temperature sintering.