Properties Of K0 Research Articles

Preparation and properties of K0.48Na0.52NbO3 ceramics for bone scaffolds via digital light processing

Lead-free piezoelectric ceramics are expected to be used for artificial bone scaffolds since they can generate electrical signals and promote recovery, but it is still difficult to fabricate piezoelectric scaffolds with complex structures. In this work, digital light processing (DLP) technology was used to fabricate potassium sodium niobate (K0.48Na0.52NbO3, KNN) bone scaffolds with gyroid triply periodic minimal surface. Suspension was first optimized to ensure both high solid loading (42 vol%) and high cure depth (>50 μm). KNN porous scaffolds (porosity: 60%) and other samples for tests were printed successfully. Then, influences of sintering temperature on microstructure, relative density and mechanical properties were discussed. Results showed that when sintered at 1090 °C, printed KNN ceramics had the highest relative density (90.11%) and lowest open porosity (5.75%), and exhibited the most satisfying mechanical properties (compressive strength: 33.85 MPa, elastic modulus: 1.87 GPa, flexural strength: 35.40 MPa, hardness: 2.39 GPa), which can meet the requirements of cancellous bone. Finally, the electric properties of samples at room temperature were verified. With d33 being 113.67 ± 2.49 pC/N and Pr being 19.94 μC/cm2, printed KNN ceramics showed comparable piezoelectric and ferroelectric performances with traditionally dry-pressed samples. These results indicated that DLP technology is competitive in preparing KNN piezoelectric bone scaffolds for implantation.

Rapid Aqueous-Phase Synthesis and Photoluminescence Properties of K0.3Bi0.7F2.4:Ln3+ (Ln = Eu, Tb, Pr, Nd, Sm, Dy) Nanocrystalline Particles

Trivalent lanthanides (Ln3+) doped bismuth-based inorganic compounds have attracted considerable interest as promising candidates for next-generation inorganic luminescent materials. Here, a series of K0.3Bi0.7F2.4 (KBF) nanocrystalline particles with controlled morphology have been synthesized through a low-temperature aqueous-phase precipitation method. Using KBF as the host matrix, Eu3+, Tb3+, Pr3+, Nd3+, Sm3+, and Dy3+ ions are introduced to obtain K0.3Bi0.7F2.4:Ln3+ (KBF:Ln) nanophosphors. The as-prepared KBF:Ln nanophosphors exhibit commendable photoluminescence properties, in which multicolor emissions in a single host lattice can be obtained by doping different Ln3+ ions when excited by ultraviolet light. Moreover, the morphology and photoluminescence performance of these nanophosphors remain unchanged under different soaking times in water, showing good stability in a humid environment. The proposed simple and rapid synthesis route, low-cost and nontoxic bismuth-based host matrix, and tunable luminescent colors will lead the way to access these KBF:Ln nanophosphors for appealing applications such as white LEDs and optical thermometry.

Dielectric Properties of Low Concentration Barium Doped K<sub>0.5</sub>Na<sub>0.5</sub>NbO<sub>3</sub> Lead Free Ceramics Prepared via Solid State Reaction Method

In this work, the effect of low concentration of Barium (Ba) on the density, crystal structure, microstructure and dielectric properties of K0.5Na0.5NbO3 (KNN) lead-free piezoelectric ceramic samples have been systematically studied. The samples were calcined at 850 °C for 6 hours and pressed using a hydraulic hand press to produce a green body disc. In this way, the green body disc of KNN was doped with 0.00 to 0.10 mol % of Ba concentration and was placed in an alumina crucible before conventional sintering at 1120 °C for 2h in air atmosphere. The increasing amount of Ba shifting all the diffraction peaks to a higher angle was measured using X-Ray Diffraction. Doping the Ba also improved the density of the KNN body. The most densified body was identified for x= 0.05 mol% of Ba which is 4.21355 g/cm3. The microstructure of the surface becomes finer and smaller after Ba doping. This shifting diffraction peaks and densified body is responsible for the enhancement of dielectric properties with the optimum value obtained from the sample doped with x= 0.05 mol%. The results show that relative permittivity (ɛr) was improved by the increment of Ba2+ concentration for 0.05 mol% which is 183.9856 for 1 kHz.

Effects of Phase and Local Structures on the Electronic and Optical Properties of K0.5na0.5nbo3 Solid Solutions

Effects of Phase and Local Structures on the Electronic and Optical Properties of K0.5na0.5nbo3 Solid Solutions

Tunable ferroelectric properties in (K0.5Na0.5)NbO3 ceramics fabricated by a simple modification of the conventional sintering technique

ABSTRACT In this work, a modified sintering method, i.e. the three-step sintering technology, has been applied to fabricate the K0.5Na0.5NbO3 ceramics. The impact of the detailed sintering conditions on the sinterability, dielectric and ferroelectric properties of K0.5Na0.5NbO3 is systematically investigated. Attributed to the three-step sintering, the highest density of 4.07 g cm−3 can be observed, which is strongly improved compared with that of the single-step sintering technique and is increased up to 90% of the theoretical density. Furthermore, through the analysis on the tunability of the dielectric and ferroelectric performances, it is found that the maxima of permittivity and polarisation can be obtained in K0.5Na0.5NbO3 sintering at 1160–1220–1120°C. These results illustrate that both the dielectric and ferroelectric behaviours can be effectively modulated through the simple modification of sintering technique, which would provide a novel route to achieve tunable electrical properties in ferroelectrics.

Structure and properties of K0.5Na0.5Nb0.96Sb0.04O3 piezoelectric ceramics doped by CuO

Envisaged through adding sintering additives to achieve low-temperature sintering preparation, in order to overcome the volatilization of sodium ions and potassium ions in the high-temperature preparation, so as to improve the density and electrical properties of KNN-based piezoelectric ceramics. This research uses traditional solid-state sintering technology, a high density, high properties lead-free piezoelectric ceramics, KNNSC-[Formula: see text], successfully prepared with sintering additives CuO. The modern test analysis of XRD and SEM shows that a moderate amount of CuO doped in the range of research can form a single perovskite structure of an orthorhombic structure, not found in any second phase, and can promote grain evenly growing and improve the sintering properties of KNN-based piezoelectric ceramics. The KNNSC-0.04 ceramics exhibit excellent electrical properties through various electrical tests such as [Formula: see text] = 238pC/N, [Formula: see text]= 47%, [Formula: see text]= 1049, tan[Formula: see text]= 2.4%, [Formula: see text] = 25.6 [Formula: see text]C/cm2, [Formula: see text] = 1.24 kV/mm, respectively. These test results show that the KNNSC-[Formula: see text] piezoelectric ceramics have great potential to be applied in middle- and low-voltage piezoelectric devices.

Effect of alkali metal (Na, K) ion ratio on structural, optical and photoluminescence properties of K0.5Na0.5NbO3 ceramics prepared by sol–gel technique

Effect of alkali metal (Na, K) ion ratio on structural, optical and photoluminescence properties of K0.5Na0.5NbO3 ceramics prepared by sol–gel technique

Phase composition and electrical properties of K0.4Na0.6Nb1−xTaxO3 lead-free thin films

Lead-free K0.4Na0.6Nb1−xTaxO3 thin films with V2O5 seed layer were prepared by chemical solution deposition method with the annealing temperatures of 675 °C. Phase composition and microstructures at room temperature were analyzed by X-ray diffraction and scanning electron microscope. The ferroelectric property and dielectric property were tested for the thin films. The results indicate that the K0.4Na0.6Nb1−xTaxO3 thin films are composed of orthorhombic and tetragonal phases, and the phase contents are affected by the content of Ta doping. The K0.4Na0.6Nb1−xTaxO3 (x = 0.015) thin film with the maximum amount of T phase content and homogeneous surface morphology obtains the best ferroelectric property and dielectric property.

The Influence of Technological Conditions on Dielectric and Optical Properties of K0.5Bi0.5TiO3 Ceramics

Lead-free ceramics of potassium-bismuth titanate K0.5Bi0.5TiO3 were obtained by a conventional sintering method under various technological conditions. The dielectric permittivity (ε) and dielectric loss (tan(δ)) measurements for these ceramics were carried out in the temperature range from 293 K to 873 K with the frequency range from 0.1 kHz to 2 MHz. An increase in dielectric permittivity with an increasing sintering temperature was observed. For the sample obtained at 1313 K and a 3.5-hour sintering time, the value of ε was about 4.55·103 (f = 100 kHz) which is twice higher than the value of ε for the sample obtained at a temperature of 1298 K and a 7-hours sintering time. For all samples, the maximum value of dielectric permittivity was shifted towards higher temperatures with an increasing frequency, which is a characteristic features of ferroelectric relaxor materials. The dielectric properties of all materials were very similar, especially in the case of dielectric loss. The values of tan(δ) at room temperature varied from about 0.07 at 0.1 kHz to 0.1 at 2 MHz. The Raman studies were performed at room temperature. No significant changes were observed for different sintering temperatures and times for all samples. The presented material can be a starting point for the development of new ferroelectric relaxor materials.

Excellent temperature stability, high relative permittivity, and piezoelectric properties of K0.5Na0.5NbO3–Bi(Li1/3Ti2/3)O3 lead-free ceramics

(1 − x)K0.5Na0.5NbO3–xBi(Li1/3Ti2/3)O3 [(1 − x)KNN–xBLT, x = 0, 0.005, 0.01, 0.015, 0.02] ceramics were prepared via a solid-state reaction method. The sintering behavior, phase structure, dielectric properties, piezoelectric performances and conductive behavior of ceramics were investigated. The BLT additive could effectively improve the performances of KNN ceramics. When x = 0.01, piezoelectric constants d33 of 145 pC/N, relative permittivity er of ~ 1551, temperature stability (Δe/e110 °C) of ± 9% (110–330 °C), dielectric loss tanδ ≤ 0.036 (101.5–388 °C) were obtained. The values of activation energy E rel and electrical conductivity activation energy E con changed from 1.1572 to 1.5918 eV and 0.8959 to 1.1088 eV, respectively. Furthermore, a possible mechanism of high temperature dielectric relaxation and conductivity could be attributed to the oxygen vacancy defect of secondary ionization.

Structural, dielectric and magnetic properties of K0.5Na0.5NbO3 and K0.5 Na0.5Nb0.975Co0.025O3 lead free ceramics

ABSTRACTLead free ferroelectric ceramics of K0.5Na0.5NbO3(KNN) and K0.5Na0.5Nb0.975Co0.025O3(KNN-Co) have been synthesized by solid state reaction method. X-ray diffraction studies reveals that both pure and cobalt doped KNN ceramics exhibits orthorhombic structure belonging to the space group Amm2. Temperature dependent dielectric measurements shows an increase in Curie temperature (TC) for KNN-Co compared to KNN. Well saturated hysteresis loops have been obtained for both compositions from the P-E loop measurements. Further, magnetic behaviour of KNN and KNN-Co ceramics have been studied.

Structure and Optical Properties of K0.67Rb1.33Al2B2O7 Crystal

A UV nonlinear optical (NLO) crystal K0.67Rb1.33Al2B2O7 (KRABO) has been obtained by the top-seeded solution growth method for the first time. Its structure is formed of coplanar [BO3]3− triangle groups and [Al2O7]8− groups, which are built from two [AlO4]5− tetrahedra sharing one vertex. Rb and K atoms have the same coordinates and locate between each layer in a disorderly fashion. The crystal has a larger NLO effect compared with its analog K2Al2B2O7 (KABO), as evidenced by powder second harmonic generation (SHG) test. The shortest SHG phase-matching wavelength is down to 231 nm according to the first-principle calculation, which indicates that KRABO is possible for the fourth harmonic generation of Nd:YAG at 266 nm.

Enhancement in the physical properties of K0.5Na0.5NbO3 ceramics by the addition of 0.5 Li2O – 0.5K2O – 2B2O3 glass

ABSTRACTThe addition of powdered 0.5 Li2O–0.5K2O–2B2O3 (LKBO) glass (0.5 to 2 wt%) to potassium sodium niobate, K0.5Na0.5NbO3 (KNN) powder facilitated higher densification which resulted in improved physical properties that include dielectric, piezoelectric and ferroelectric. The required polycrystalline powders of KNN were synthesized through solid-state reaction route, while LKBO glass was obtained via the conventional melt-quenching technique. Pulverized glass was added to KNN powders in different wt% and compacted at room temperature and these were sintered around 1100°C. Indeed the addition of optimum amount (1 wt %) of LKBO glass to KNN ceramics facilitated lowering of sintering temperature accompanied by larger grains (8 µm) with improved density. The dielectric constant (ϵr) measured at room temperature was 475 (at 10 kHz), whereas it was only 199 for the LKBO glass free KNN. The piezoelectric coefficient (d33) was found to be 130 pC/N for 1 wt% LKBO added glass, which was much higher than that of pure KNN ceramics (85 pC/N). Indeed, the LKBO glass added samples did exhibit well saturated P versus E hysteresis loops at room temperature. Though there was no particular trend observed in the variation of Pr with the increase in glass content, the Pr values were higher than that obtained for KNN ceramics. The improved physical properties of KNN ceramics encountered in these studies were primarily attributed to enhancement in density and grain size.

The effect of some transition metal oxides on the physical properties of K0.5Na0.5Nb0.95Ta0.05O3 ceramics

Both K0.5Na0.5Nb0.95Ta0.05O3 (KNNTO) and (K0.5Na0.5Nb0.95Ta0.05O3)0.99-M0.01, M = Co3O4 and Mn2O3 (M/KNNTO) Ferromagnetic behaviour was observed for some M/KNNTO compounds. The hardness and compressive strength of all investigated samples are given. Comparisons with similar materials are discussed. Ceramics were synthesised using a solid-state reaction method. X-ray diffraction patterns of all samples revealed that the crystal structure is orthorhombic. Field-emission scanning electron microscopy was performed. Polarisation hysteresis curves indicated a disruption of ferroelectric order with the addition of M into KNNTO ceramics. The dielectric properties of the investigated ceramics have been studied as a function of frequency and temperature.

Effects of rare-earth (Tb, Yb, and Lu)-doping on the structural, electrical and ferroelectric properties of K0.5Bi4.5Ti4O15 thin films

The electrical and the ferroelectric properties of pure K0.5Bi4.5Ti4O15 and a series of rare-earth-doped K0.5RE0.5Bi4Ti4O15 (RE = Tb, Yb, and Lu) thin films deposited on Pt(111)/Ti/SiO2/Si(100) substrates by using a chemical solution deposition method have been investigated. Compared to the pure K0.5Bi4.5Ti4O15 thin film, there were no structural changes in the K0.5RE0.5Bi4Ti4O15 thin films while the leakage current and the ferroelectric properties were significantly improved. Among the thin films, the K0.5Lu0.5Bi4Ti4O15 thin film exhibited wellsaturated hysteresis loops with a large remnant polarization (2Pr) of 32 μC/cm2 and a coercive field (2Ec) of 307 kV/cm at an applied electric field of 886 kV/cm. Furthermore, a low leakage current density of 2.95 × 10−9 A/cm2, which is about two orders of magnitude lower than that of the K0.5Bi4.5Ti4O15 thin film, was measured in the K0.5Lu0.5Bi4Ti4O15 thin film at an applied electric field of 100 kV/cm. The enhanced electrical and ferroelectric properties observed in the rare-earthdoped K0.5RE0.5Bi4Ti4O15 thin films can be correlated to a decrease in the number of ionic defects, such as bismuth and oxygen vacancies, structural distortion, and improved microstructure.

Effect of Eu Doping on the Structural, Electrical, and Dielectric Properties of K0.5Na0.5NbO3 Ceramics for High-Temperature Capacitor Applications

The structural and dielectric properties of Eu-doped K0.5Na0.5NbO3 (KNN) ceramics were investigated as a potential candidate for use in high-temperature capacitors with working temperature beyond 200°C. x-Ray diffraction results showed that tetragonal and cubic structure distortions occurred for low- and high-concentration doping, respectively. With increase of Eu content, the dielectric anomaly of the tetragonal–cubic transition was depressed and shifted to low temperature, while the temperature of the orthorhombic–tetragonal transition remained unchanged. A dielectric relaxation associated with oxygen vacancies was detected in the paraelectric phase region. The activation energy of oxygen vacancies depended on the Eu concentration and the defect compensation mechanism. KNN doped with 3 mol% Eu (KNN3Eu) showed good dielectric temperature stability (±10%) with relatively high permittivity (>1800 at 225°C) over the temperature range from 119°C to 495°C, representing a good starting point for development of high-temperature capacitor materials.

Structure and temperature-stability of piezoelectric properties of K0.5Na0.5NbO3–LiSbO3–Al(Fe0.9Mn0.1)O3 lead-free ceramics

(1 − x)(0.95K0.5Na0.5NbO3–0.05LiSbO3) − xAl(Fe0.9Mn0.1)O3 (KNN–LS–AFM) lead-free piezoelectric ceramics have been fabricated by a traditional ceramic technique. The structure and piezoelectric properties of this system have been studied. The result of X-ray diffraction analysis shows that LS and AFM diffuse into the KNN lattices to form a new solid solution with a perovskite structure. The phase structure of the ceramics has a transition from the coexistence of tetragonal and orthorhombic phases to single tetragonal phase, with increasing the AFM content. The orthorhombic–tetragonal phase-transition peaks in the temperature-dielectric constant (er) plots first shifts to the room temperature and then almost disappears, while the Curie temperature does not change evidently with the addition of AFM. The ceramic at x = 0.004 exhibits the best piezoelectric properties: d33 = 285 pC/N, kp = 53.9 %, Qm = 22.64. The Curie temperature is about 350 °C. Below the Curie temperature, all samples show a temperature-stable piezoelectric constant, indicating the possibility of applications from the room temperature to high temperature.

Dielectric, Electromechanical, and Elastic Properties of K1−x(NH4)xH2PO4 Compounds

We present the results of the thermodynamic theory of piezoelectric ferroelectrics and of the phenomenological theory of thermodynamic characteristics of the KH2PO4 type ferroelectrics. Available experimental data for the dielectric, piezoelectric, and elastic characteristics of the K1−x(NH4)xH2PO4 type systems are described using the proposed microscopic theory of these crystals.

Antiferromagnetism in Fe1+y Te and Superconductivity in K x Fe2Se2

Iron-based layered chalcogenides are interesting because of their structural magnetic and superconducting properties. Single crystals of the parent binary chalcogenides, Fe1+y Te, and intercalated ternary chalcogenides, K0.8Fe2Se2, are grown and investigated in detail. Single crystals are grown by modified horizontal Bridgman method. Fe1+y Te demonstrates an antiferromagnetic (AFM) transition at T (N) =67 K which is identified as a magnetostructural transition. By varying the concentration of excess Fe, we have tuned T (N) over a range of temperature from 67 to 57 K. The superconducting properties of K0.8Fe2Se2 crystals are explored by magnetization measurements. A superconducting transition is observed at T (C) =31 K. The lower critical field of K0.8Fe2Se2 is estimated from field variation of magnetization measurements.

Preparation and Ferroelectric Properties of K0.5Na0.5NbO3 Thin Films Derived from Non-alcohol Niobium Salt Sol-gel Process

Lead-free K0.5Na0.5NbO3 (KNN) thin films were prepared on Pt (111) /Ti/SiO2/Si (100) substrates by a polyvinylpyrrolidone (PVP)-modified sol-gel method without any metal alkoxides. The effects of PVP on the crystallization, surface morphology and electrical properties were investigated. It was found that the introduction of PVP into the sol could reduce the annealing temperature, enhance the surface quality and improve the KNN film of (100) oriented growth. Compared with the pure non-PVP-modified KNN thin films, the dielectric and ferroelectric properties of the KNN films were significantly enhanced by adding PVP into the sol. In particular, the PVP-modified KNN films which were annealed at 550°C exhibited relatively saturated polarization-electric field (P-E) hysteresis loops with high remnant polarization Pr of 22 μC/cm2, dielectric constant of 280 and dielectric loss of 0.09, respectively, indicating promising lead-free piezoelectric film candidate for future applications.