Sodium Niobate Ceramics Research Articles

Structure and domain wall dynamics in lead-free KNN-based ceramics

This paper comprehensively studied the effect of BaHfO3 doping on crystal structure, domain structure, and electrical properties of potassium sodium niobate ceramics, and especially analyzed the intrinsic structural characteristics of the R-O phase boundary, which can be successfully constructed through composition modification. Rietveld refinement and the piezoresponse force microscopy technique were combined to analyze the crystal structure and domain configuration of the material system. Comparative studies indicate that multiple phase coexistence will disturb the zigzag domains of the pure O phase into complex irregular domains, which are easier to switch under an external electric field, thus leading to improved electrical properties. Furthermore, the stabilized polarization state can be maintained under the thermal excitation due to the dominated O phase at high temperatures, which is beneficial for the temperature stability improvement. We believe that the structural analysis can give us a deeper understanding of the relationship among structural symmetry, domain dynamics, and electrical properties of potassium sodium niobate (KNN)-based ceramics.

Potassium sodium niobate ceramics with broad phase transition range: Temperature-insensitive strain

Excellent piezoelectric properties have been achieved in (K,Na)NbO3 (KNN)-based ceramics in the past few years. However, temperature-sensitive strain restricts the use of these ceramics in practical applications. In this work, we report improved piezoelectricity and temperature-insensitive strain in KNN-based ceramics. A broad temperature range for phase boundaries is formed by composition optimization, accounting for the observation of a highly improved strain stability. Interestingly, the strain for a ceramic with x = 0.025 varies by less than 5% and 9%, even if the temperature reaches 150 °C and 170 °C, respectively, which is comparable to that found for textured-LF4T ceramics. Furthermore, the stability of the original domain configuration with increasing temperature is tested to understand the underlying mechanism for the temperature-insensitive strain. The huge number of original domains retaining a piezoresponse at high temperature due to the extended phase boundary contributes to the temperature-insensitive strain. The present results open a new window for KNN-based ceramics to be used in applications demanding temperature-insensitive piezoelectric properties.

Isolation of a ferroelectric intermediate phase in antiferroelectric dense sodium niobate ceramics

Switchable ferroelectric/antiferroelectric ceramics are of significant interest for high power energy storage applications. Grain size control of this switching is an interesting approach to controlling polarization and hence dielectric properties. However, the use of this approach in technologically relevant ceramics is hindered by difficulty in fabricating dense ceramics with small grain sizes. Here an intermediate polar ferroelectric phase (P21ma) has been isolated in dense bulk sodium niobate ceramics by grain size control through spark plasma sintering methods. Our findings, supported by XRD, DSC, P-E (I-E) loops and dielectric characterization, provide evidence that the phase transition from the antiferroelectric (AFE) R-phase, in space group Pnmm, above 300 °C, to the AFE P-phase, in space group Pbma, at room temperature, always involves the polar intermediate P21ma phase and that the P21ma → Pbma transition can be suppressed by reducing grain size.

The effect of A-site nonstoichiometry on the microstructure, electric properties, and phase stability of NaNbO3 polycrystalline ceramics

The impact of A-site nonstoichiometry on the microstructure, electric properties, and phase stability of sodium niobate ceramics (Na1+xNbO3, x = −2 to 1 mol %) was investigated. All the components maintained an orthorhombic antiferroelectric (AFE) structure. The grain size increased from 3.9 to 14.3 μm with the variation in x from −2 to 1. The AFE–FE phase transition electric field dramatically increased from 100 kV cm−1 at x = 0 to 170 kV cm−1 at x = −2, confirming the enlarged energy barrier between AFE Pbma and FE Pmc21 phase under external field in A-site deficient components. This is attributed to the lattice compressive stress generated by introducing proper A-site vacancies. Combined results of transmission electron microscopy and Raman spectroscopy indicated that the AFE distortion of Pbma phase was significantly enhanced in A-site deficient components, which jointly contributed to the stability of AFE phase in A-site deficient NaNbO3 material.

Effect of tantalum on the temperature dependent electrical characteristics of NaNb1−xTaxO3 (0.0 [formula omitted] x [formula omitted] 0.3) ceramics between 400 and 560 °C

NaNb1−xTaxO3 (x = 0.0, 0.1, 0.2 and 0.3) (NT0, NT1, NT2 and NT3) ceramics are synthesized by conventional solid state reaction technique at high sintering temperature 1150 °C for 4 h. The crystallinity and surface morphology are studied by X - ray diffraction (XRD) and Field emission scanning electron microscopy (FE-SEM) at room temperature, respectively. XRD analysis of Ta ion doped sodium niobate ceramics confirms the formation of single phase with orthorhombic symmetry. In FE - SEM analysis, the effect of tantalum (Ta) ion on the grain growth of NT ceramics is clearly noticeable. With increasing the amount of Ta ion in NT ceramics, size of grains get diminished. The dielectric and impedance behavior of NT material are studied as a function of frequency (100 Hz - 5 MHz) at selected temperature (400 °C - 560 °C). The maximum value of real permittivity (ε') is obtained in NT3 ceramics at 560 °C temperature. The impedance analysis of NT ceramics confirms that the relaxation peaks shift toward higher frequency with a rise in temperature. Such type of change in relaxation peak is attributed to the temperature dependent time relaxation phenomenon present in material.

Technology and electrophysical properties of the (K0.44Na0.52Li0.04)(Nb0.9–xTa0.1Sbx)O3 ceramics

ABSTRACTCompounds based on (KzNa1–z)NbO3 (KNN) are promising lead-free ferroelectric materials that reveal good electrophysical properties. In the present work, we report the results of the study influence of the doping effect of antimony on the technology, microstructure and electrophysical properties of potassium sodium niobate ceramics modified by lithium and tantalum ions (K0.44Na0.52Li0.04)(Nb0.9–xTa0.1Sbx)O3 (KNLNTSbx). The four KNLNTSbx ceramic compositions were designed:(K0.44Na0.52Li0.04)(Nb0.9Ta0.1)O3 (for xSb = 0),(K0.44Na0.52Li0.04)(Nb0.88Ta0.1Sb0.02)O3 (for xSb = 0.02),(K0.44Na0.52Li0.04) (Nb0.87Ta0.1Sb0.03)O3 (for xSb = 0.03),(K0.44Na0.52Li0.04) (Nb0.86Ta0.1Sb0.04)O3 (for xSb = 0.04).All ceramic powders were synthesised by the standard solid-state reaction method from the mixture of oxides and carbonates. The paper presents the technology and results of crystal structure, microstructural, dielectric properties, as well as DC electrical conductivity of the KNLNTSbx ceramics. The conducted research proved that suitable doping of the KNN materials improves the sinterability of the ceramic compositions and positively influences the useful electrophysical properties thereof.

The influence on sintering and properties of sodium niobate (NaNbO3) ceramics by “non-stoichiometric” precursor compositions

Abstract NaNbO3 powders from different processing routes and various near equimolar concentrations of metal ions were sintered to ceramics and investigated concerning their structural and electric properties. The particle sizes obtained from two different conventional solid state reactions and one solvent – based route were in the range of 40 nm - 10 μm and the variation of precursor composition covered 48–52 mol% Na. Sintering temperatures were defined by the deviation from the equimolar composition between 950 and 1375 °C, which is due to the coexistence of second phases Na3NbO4, Na2Nb4O11 and NaNb3O8. Small particle sizes (40 nm–3 μm) on deviation from equimolar composition resulted in higher relative densities at lower sintering temperatures. The coexistence of second phases influences structural and electric characteristics. The former were investigated by X-ray Diffraction (XRD) for phase analysis, Scanning Electron Microscopy (SEM) for defining grain sizes and Energy-Dispersive X-ray (EDX) spectroscopy for deciding the elemental composition. The impact on electrical conductivity and dielectric properties are examined by impedance spectroscopy and the resulting d33 coefficients of 15–29 pC/N are measured by Berlincourt method.

Understanding the piezoelectricity of high-performance potassium sodium niobate ceramics from diffused multi-phase coexistence and domain feature

Unveiling the physical mechanisms of high performance in potassium sodium niobate-based ceramics from diffused multi-phase coexistence and a single domain feature.

Effect of cobalt substitution on the multiferroic characteristics of ferroelectric potassium sodium niobate (K0.5Na0.5NbO3) ceramics

The room-temperature multiferroic behavior of cobalt-substituted KNN [K0.5Na0.5Nb1−xCoxO3, 0.02 ≤ x ≤ 0.05] ceramics has been investigated. Both the X-ray diffraction and selected area electron diffraction analysis confirm that all the compositions found to be crystallized in the single phase (Orthorhombic, Amm2) without any formation of cobalt clusters and/or other secondary phases such as Co3O4. Co2+ oxidation state and the presence of oxygen vacancies in the samples have been studied through X-ray photoelectron spectroscopic measurements. The changes in the bandgap with the increase of Co concentration in KNN are noticed from UV–Visible absorption spectroscopy. Magnetic measurement on the samples reveals a dominant antiferromagnetic interaction attributed to the Co2+–Co2+ exchange interactions via F0-center and coupling between Co2+–Co2+ through O2−. The existence of exchange bias (EB) effect is also observed in KNaNb1−xCoxO3 (x = 0.03, 0.04, 0.05) samples from the magnetic measurements. In addition, it is found that defect complexes formed between \({\text {Co}^{'''}_{\text{Nb}}}\) and oxygen vacancy lead to the enhanced dielectric, ferro, and piezoelectric properties of K0.5Na0.5Nb1−xCoxO3 ceramics.

Structural, optical and photoluminescence properties of K0.5Na0.5NbO3 ceramics synthesized by sol–gel reaction method

Potassium sodium niobate (KNN) ceramics have been prepared by sol–gel route. The effect of conventional sintering on its optical and photoluminescence properties has been studied. Optical measurements were done by reflectance measurements of the ceramics which showed decrease in optical band gap energy with an increase in sintering temperature. A room temperature photoluminescence (PL) spectrum was taken at an excitation wavelength of 300 nm. The existence of green emission confirms the existence of oxygen vacancies in the sample. Raman spectroscopy analysis revealed changes in Raman scattering mode for KNN ceramics sintered at different temperatures. I–V characteristics have been studied from 20–180 V disclosed that increase in sintering temperature favor higher order of leakage current at room temperature.

Coexistence of electric polarization and magnetic ordering in acceptor doped potassium sodium niobate (KNN) ceramics

Lead-free single-phase multiferroic K0.5Na0.5Nb1−xFexO3 (x = 0.02, 0.03, 0.04, 0.05) ceramics have been synthesized by solid-state reaction method to explore the simultaneous existence of ferroelectric and magnetic order. X-ray diffraction analysis of the samples confirms no phase separation and impurity phase formation with the increase of Fe2O3 concentration. The morphology, lattice fringes and SAED pattern of KNN ceramics studied from HR-TEM studies. The structural transition from orthorhombic—tetragonal (TO−T) and tetragonal—cubic (TC) have been studied for all compositions through temperature dependent dielectric measurements. Existence of Fe in multi-oxidation states such as Fe2+, Fe3+ and oxygen vacancy have been studied through X-ray photoelectron spectroscopy (XPS) analysis. Lowering of band gap noticed for all the Fe doped KNN samples from UV/Vis absorbance studies. Presence of defect dipoles such as and oxygen vacancies leads to pinning of domains give rise to asymmetric P-E and S-E response. Further, the observed intrinsic magnetic ordering in K0.5Na0.5Nb1−xFexO3 could be explained through various exchange interactions.

Structure, electricity, and bandgap modulation in Fe2O3–doped potassium sodium niobate ceramics

Perovskite materials possess promising application prospects in photovoltaics and are most likely to replace the dominance of silicon-based solar photovoltaic materials. (K0.5Na0.5)NbO3–xFe2O3 perovskite ferroelectric ceramics (x = 0, 0.01, and 0.05) were prepared using a conventional solid-state reaction method. We systematically analyzed the structural, morphological, electric, magnetic, and optical properties. Structural and morphological features of the as-prepared ceramics show that the phases of the materials all are orthorhombic. The appropriate amount of Fe2O3 introduced will improve the electrical properties. Magnetic switching corresponding to a diamagnetic-ferromagnetic transformation was observed. Bandgap (Eg) modulation was achieved in the Fe2O3-doped KNN ceramics, with the Eg exhibiting a drastic decrease as the doping content increased in experiment where the Eg = 2.886, 2.232, and 2.061 eV when x = 0, 0.01, and 0.05, and the CASTEP calculation shows a similar trend, indicating that the materials exhibit a higher performance with the absorption in visible light.

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.

A composition design rule for crystal growth of centimeter scale by normal sintering process in modified potassium sodium niobate ceramics

It has been reported that single crystals could be grown by normal sintering process, without the addition of a seed, in (K,Na)NbO3 (KNN)-based ceramics. The growth of huge grains (approximately 5–30mm) is due to the donor effect on abnormal grain growth (AGG) in KNN-based ceramics. In this study, a composition design rule is suggested to obtain the large single crystal without the seed addition in KNN-based ceramics. In addition, it is also identified by the microstructure observation that the huge grains can be due to the donor effect on the abnormal grain growth which is found in perovskite materials. The donor ratio must be designed to be located at the range between 0.7% and 0.9% compared to that of Na+ ions, in order to obtain the large single crystals in KNN-based ceramics. This range of the donor ratio is narrower than that in BaTiO3 (or SrTiO3) ceramics.

Effect of addition of V2O5 on the densification, dielectric and ferroelectric behavior of lead free potassium sodium niobate ceramics

ABSTRACTPotassium sodium niobate (KNN) ceramics were prepared by solid state synthesis followed by liquid phase sintering using V2O5 as a sintering aid. Sintering at 1120 ºC for 4 hours using V2O5 caused significant improvement in relative density with maximum relative density reaching to more than 94%. Dense polycrystalline ceramics having grain size about 2 µm were obtained as a result of liquid phase sintering. Gradual improvement in dielectric constant was observed with increase in V2O5 content coupled with increase in electrical conductivity. Maximum remnant polarization of 18 µC/cm2 was recorded for ceramic sintered with 5 wt% V2O5.

Fabrication of Biocompatible Potassium Sodium Niobate Piezoelectric Ceramic as an Electroactive Implant.

The discovery of piezoelectricity in natural bone has attracted extensive research in emulating biological electricity for various tissue regeneration. Here, we carried out experiments to build biocompatible potassium sodium niobate (KNN) ceramics. Then, influence substrate surface charges on bovine serum albumin (BSA) protein adsorption and cell proliferation on KNN ceramics surfaces was investigated. KNN ceramics with piezoelectric constant of ~93 pC/N and relative density of ~93% were fabricated. The adsorption of protein on the positive surfaces (Ps) and negative surfaces (Ns) of KNN ceramics with piezoelectric constant of ~93 pC/N showed greater protein adsorption capacity than that on non-polarized surfaces (NPs). Biocompatibility of KNN ceramics was verified through cell culturing and live/dead cell staining of MC3T3. The cells experiment showed enhanced cell growth on the positive surfaces (Ps) and negative surfaces (Ns) compared to non-polarized surfaces (NPs). These results revealed that KNN ceramics had great potential to be used to understand the effect of surface potential on cells processes and would benefit future research in designing piezoelectric materials for tissue regeneration.

Investigation of new lead free (1−x)KNNS–xBKZH piezo-ceramics with R–O–T phase boundary

In this work, lead free piezo-ceramics of (1−x)K0.4Na0.6Nb0.96Sb0.04O3–xBi0.5K0.5Zr0.9Hf0.1O3 [(1−x)KNNS–xBKZH] have been synthesized by conventional solid-state sintering method. The effect of BKZH content on the phase structure and electrical properties were systematically investigated. The results show that a coexistence of rhombohedral–orthorhombic–tetragonal (R–O–T) phases have been found when x = 0.04, indicating that BKZH doping can induce the formation of R–O–T phase boundary by increasing T R−O and decreasing T O−T simultaneously in KNN systems. In addition, an optimal electrical properties (e.g., d 33 = 451 pC/N, k p = 52%, T c = 258 °C, e r = 2489, tanδ = 3.6%, P r = 21.7 μC/cm2, and E c = 10.1 kV/cm) were obtained in the ceramic of x = 0.04, which proves that adding BKZH content is an efficientive way to promote the electrical properties of potassium–sodium niobate ceramics. As a result, we can believe that the (1−x)KNNS–xBKZH ceramics will become one of the promising lead-free candidates for piezoelectric applications.

Enhanced electrocaloric effect near polymorphic phase boundary in lead-free potassium sodium niobate ceramics

The electrocaloric (EC) effect in lead-free (1-x)(K0.48Na0.52)(Nb0.95Sb0.05)O3-xBi0.5(Na0.82K0.18)0.5ZrO3 ceramics was investigated using an indirect thermodynamic method. Large EC temperature changes were obtained in the vicinity of a polymorphic phase boundary at 40 kV/cm, e.g., 0.32 K at 359 K for x = 0.03, 0.51 K at 350 K for x = 0.04, and 0.48 K at 300 K for x = 0.05, respectively. These values are larger than the previous results at inter-ferroelectric phase transition and, more interestingly, are found to be comparable to those usually explored at the Curie temperature. The operational temperature window is broad near the polymorphic phase boundary due to the diffuseness of the phase transition. The enhanced electrocaloric effect is attributed to the formation of nanodomains near the polymorphic phase boundary, which reduces domain wall energy and facilitates the polarization rotation. The construction of a polymorphic phase boundary and the arrangement of coexisting phases at the nanoscale may open a promising route to explore EC materials.

Composition Design for Growth of Single Crystal by Abnormal Grain Growth in Modified Potassium Sodium Niobate Ceramics

In this manuscript, it is reported how the composition can be designed, in order to obtain large crystals (>2 cm, required for device application) through the abnormal grain growth (AGG) in (K,Na)NbO3 (KNN)-based ceramics. The AGG of KNN-based ceramics can be expedited by considering three factors, such as the stoichiometry of compositions, the large amount of liquid phase, and the donor-doping to enhance the growth rate of a large grain. The composition of (1 – x)(K0.5Na0.5)NbO3 – xBa(Cu1/3Nb2/3)O3 (KNN – xBCuN) was designed to satisfy the three factors. A Ba2+ ion was a donor in KNN and CuO was added to form the large amount of liquid phase. During the sintering process, Cu ions melt into the liquid phase of KNN ceramics and Ba2+ ions enter the vacant sites of Na+ ions. Therefore, Ba2+ ions can compensate for the Na+ loss in KNN – xBCuN ceramics. The growth rate of large grains was enhanced approximately 1000 times and the single crystal (approximately 3 cm) was successfully obtained. In addition, this single crystal showed an excellent sensor property and Curie temperature, which were higher than those of PZT-based single crystals.

Microwave dielectric properties of potassium sodium niobate ceramics with different K/Na ratios

Potassium sodium niobate (KxNa1−xNbO3) ceramics with different K/Na ratios were prepared by traditional solid reaction method and the complex permittivity at 8.2–12.4GHz was measured in this study. Then the complex permittivity at GHz was compared with that at low frequency (KHz and MHz). And the influences of phase structure and microstructure on the dielectric properties were investigated. A lattice parameter discontinuity at x=0.5 was found and the ceramic with x=0.5 has well faceted and homogeneous grain size distribution compared with others. In addition, the reflection loss of the ceramics was calculated. All the ceramics possess better absorption property at the frequency around 11GHz, while the effective absorption bandwidth is narrow. The ceramic with x=0 shows the best absorption property because of its relatively low dielectric permittivity.