FTIR and dielectric studies of nickel doped potassium hexa-titanate (K2Ti6O13) fine ceramics

The dielectric and electrical properties such as relative permittivity $(\varepsilon^{\prime } )$ , loss tangent (tanδ), and ac conductivity (σ_ac) have been studied in the temperature range 373–773 K at three different frequencies 100, 200, 400 kHz for doped potassium hexa-titanate (K₂Ti₆O₁₃) samples. It was observed that dielectric constant and loss tangent decreases while ac conductivity increases with the increase in frequency. The temperature dependent relative permittivity showed a phase transition for all samples. Dielectric loss mechanism was observed to include space charge polarization and dipole orientation. Moreover, electron-hopping conduction was observed to be dominant in the low temperature region, whereas intratunnel ionic conduction prevailed at higher temperatures. Fourier transform infrared spectroscopy analysis was also carried out to identify the chemical bonds present in the specimens.     

Dielectric–spectroscopic and AC conductivity studies in iron doped layered Na2Ti3O7 ceramics

The results of AC electrical conductivity studies in Na₂Ti₃O₇ doped with 0.1 and 1.0 mol% of iron have been reported in the temperature range of 373–773 K. The corresponding log(σ_ACT) versus 1000/T plots have been divided into four distinct regions, namely I, II, III and IV. Lowest temperature region I is attributed to electronic hopping with exchangeable interlayer ionic conduction, in region II associated interlayer ionic conduction is dominated over electronic hopping conduction. Moreover, the conduction in the next region III is due to co-existence of hindered interlayer ionic and suppressed electronic hopping conduction, while conduction in highest temperature region IV is modified interlayer ionic conduction. Dielectric loss (tan δ) and dielectric constant (ɛ) versus frequency plots at different temperatures have also been described. Furthermore, the results of tan δ and ɛ versus temperature at various frequencies have been reported for iron doped Na₂Ti₃O₇ samples. The losses are the characteristic of dipole mechanism in both the samples. The possibility of ferroelectric phase transition is proposed in this paper.     

Dielectric properties of bismuth doped CaCu3Ti4O12 ceramics

Ca_1?3x/2Bi_xCu₃Ti₄O₁₂ (x = 0.0–0.3) ceramics were prepared by the conventional solid-state reaction method. X-ray powder diffraction analysis confirmed the formation of cubic CCTO phase except for subtle peaks of CuO. SEM micrographs suggested that the morphologies of doped CCTO ceramics had been sheet-like for high Bi-doping amount, and the dominant grain size decreasing could be seen for the small content of Bi-doping CCTO. Dielectric properties of pure and doped CCTO were investigated in a broad temperature range of 20–420 K. The results showed that bismuth doping could decrease the dielectric loss but suppress the dielectric temperature stability at the same time. Bi doped CCTO ceramics presented different relaxation properties. As to pure CCTO and BCCTO (x = 0.3) only one MW relaxation (Relaxation I) could be found, which moves to higher frequency with temperature increasing. However, two relaxation processes (Relaxation I and II) appear for BCCTO (x = 0.1–0.2). By means of complex impedance spectra analysis and Arrhenius fitting, we successfully separated the different conductive segments and explained the mechanisms of the two relaxation processes. Relaxation I appeared at low temperature could be attributed to the V_O doping energies inside CCTO grains which did not showed significant changing of activation energy after bismuth doping. For Relaxation II at higher temperature than Relaxation I, with activation energy obviously depending on the Bi-ion concentration, may be related with the V_O point defects at the grain boundaries.     

K2Ti6O13-TiO2／Ti生物陶瓷材料的微弧氧化法制备

通过微弧氧化成功的在两种含钾的电解质中制备了K2Ti6O13-TiO2/Ti复合生物陶瓷材料.XRD检测表明制备得到的陶瓷膜的主要成分是K2Ti6O13和金红石型TiO2,还有少量的锐钛矿型TiO2和K2Ti4O9.EDX线扫描检测结果说明陶瓷膜中的各相是相互交织的结合在一起的,能提高陶瓷膜与钛基体的结合强度.表面SEM形貌检测显示表面呈现多微孔的陶瓷结构.两种体系中制备的陶瓷膜经仿生溶液浸泡6d后能检测到明显的片状结构的HAp涂层,表明K2Ti6O13-TiO2/Ti生物陶瓷材料具有很强诱导HAp沉积的能力,生物活性很好.分析结果表明K2Ti6O13和金红石型TiO2成分的存在是陶瓷膜具有良好生物活性的关键所在.     

钛合金表面K2Ti6O13w涂层的制备及其生物活性

K2Ti6O13晶须不仅具有优越的力学性能和良好的生物学特性,而且具有与常规Ti合金相近的膨胀系数。本研究尝试选用K2Ti6O13晶须（K2Fi6O13w）作为生物活性涂层材料,利用BCC方法（混合-包埋-煅烧）在Ti合金基体上成功制备了K2Ti6O13w涂层,并对涂层的表面形态、结合强度和生物活性进行了研究。结果表明,涂层由K2Ti6O13晶须和少量的TiO2和K2Ti6O9组成,其表面粗糙多孔。由于膨胀系数的良好匹配,涂层与基体之间具有较高的结合强度,达24MPa。模拟体液培养后,涂层表面沉积了一层多孔的骨状羟基磷灰石,它由平均直径20nm,长200nm的羟基磷灰石纳米线组成,这表明钛酸钾涂层具有良好的生物活性。涂层较高的生物活性与其独特的生化特性和组分密切相关。     

K2Ti6O13 Nanoparticle-Loaded Porous rGO Crumples for Supercapacitors

One-dimensional alkali metal titanates containing potassium,sodium,and lithium are of great concern owing to their high ion mobility and high specific surface area.When those titanates are combined with conductive materials such as graphene,carbon nanotube,and carbon nanofiber,they are able to be employed as efficient electrode materials for supercapacitors.Potassium hexa-titanate(K2Ti6O13,KTO),in particular,has shown superior electrochemical properties compared to other alkali metal titanates because of their large lattice parameters induced by the large radius of potassium ions.Here,we present porous rGO crumples(PGC)decorated with KTO nanoparticles(NPs)for application to supercapacitors.The KTO NP/PGC composites were synthesized by aerosol spray pyrolysis and post-heat treatment.KTO NPs less than 10 nm in diameter were loaded onto PGCs ranging from 3 to 5μm.Enhanced porous structure of the composites was obtained by the activation of rGO by adding an excessive amount of KOH to the composites.The KTO NP/PGC composite electrodes fabricated at the GO/KOH/TiO2 ratio of 1:3:0.25 showed the highest performance(275 F g−1)in capacitance with different KOH concentrations and cycling stability(83%)after 2000 cycles at a current density of 1 A g−1.     

Molten salt synthesis of single-crystalline K2Ti6O13 annular nanostructures

Single-crystalline K2Ti6O13 ring-like structures have been synthesized via a simple molten salt method without any templates and surfactants. The annular structures have several different types, such as nanoring, wheel-like and diskette-like ring. Each type of rings was characterized individually by scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). These annular structures are formed by the loop-by-loop self-coiling of K2Ti6O13 nanobelts in the ring plane. The driving force of self-coiling is suggested to minimize the local electrostatic energy introduced by spontaneous polarization.     

Interfacial reactions in K2Ti6O13(w)/Al2O3/Al composite

Abstract

A pure Al matrix composite, reinforced by potassium titanate whiskers coated with sol–gel alumina, was fabricated by squeeze casting. Good interface bonding was achieved in the coated composite. Interfacial reactions in the composite were found to be less severe than those in an uncoated composite, owing to the barrier effect of sol–gel -Al₂O₃ coating. After the composite was thermally exposed at 530°C for 30 h, the alumina coating still restrained the decomposition of the whisker structure, and thus prevented a decrease in the strength of the composite. However, after a thermal exposure at 700°C for 10 h, the coating was no longer held on whisker surfaces. Mechanical testing showed that tensile fracturing of the coated composite tended to occur at the coating/matrix interface where the interfacial bonding is weaker than at the coating/whisker interface.     

Preparation and dielectric properties of Sr(Ti0.95Zr0.05)O3 ceramics doped with CaOTiO2SiO2 (CTS)

Sr(Ti_0.95Zr_0.05)O₃ ceramic was sintered using x mol.% CTS (x = 0, 0.5, 1.5, 4, 7) as sintering additive for the first time. Although Sr(Ti_0.95Zr_0.05)O₃ ceramic could not be fully sintered even at 1420 °C, the densification temperature could be decreased to 1280 °C by using CTS, which begin melting when temperature reaches higher than 1150 °C. The microstructures of the samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM). Apparent density and the dielectric properties were established at room temperature. The measuring frequency was 1 MHz. The microstructure and dielectric properties greatly changed depending on the amount of CTS additive. The optimum concentration to obtain nicer dielectric properties was 0.5 mol.%.     

Environmentally friendly growth of single-crystalline K2Ti6O13 nanoribbons from KCl flux

Single-crystalline K₂Ti₆O₁₃ nanoribbons with typical width ranging from one hundred nanometers to a few hundred nanometers and length up to tens of microns were prepared from KCl flux. The nanoribbons were characterized by a range of methods including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy, selected area electron diffraction and high-resolution transmission electron microscopy. Ultraviolet–visible experiments showed that the K₂Ti₆O₁₃ nanoribbons were wide-band semiconductors with a band width E_g = 3.4 eV. The mechanism of one-dimensional growth of the nanoribbons was attributed to the oriented attachment mechanism.     

K2Ti6O13晶须改性硅酸盐无机胶粘剂的研究

以K2Ti6O13晶须为改性剂制备了一种改性硅酸盐胶粘剂.采用AG-250KNI电子精密材料试验机和DTG60H差热-热重分析仪对胶粘剂的力学性能和耐热性能进行了表征,采用常温水浸实验对胶粘剂的耐水性能进行了评价.结果表明,K2Ti6O13晶须有效的改善了胶粘剂的粘接强度、耐水性能和耐热性能.运用GBC10e紫外-可见分光光谱仪研究了K2Ti6O13对胶粘剂的改性机理.     

BaNb2O6掺杂Na1/2Bi1/2TiO3无铅压电陶瓷的介电弛豫

采用传统陶瓷制备方法,制备了无铅新压电陶瓷材料Na1/2Bi1/2TiO3-xBaNb2O6.研究了BaNb2O6掺杂对(Na1/2Bi1/2)TiO3陶瓷晶体结构、介电性能与介电弛豫行为的影响.XRD分析表明,在所研究的组成范围内陶瓷材料均能够形成纯钙钛矿固溶体.材料的介电常数-温度曲线显示陶瓷具有两个介电反常峰Tf和Tm,修正的居里一外斯公式较好的描述了陶瓷弥散相变特征,弥散指数随BaNb2O6掺杂量的增加而增加.该体系陶瓷表现出与典型弛豫铁电体明显不同的弛豫行为,低掺杂量的陶瓷仅在低温介电反常峰Tf附近表现出明显的频率依赖性,而高掺杂的陶瓷材料在室温和Tf之间都表现出明显的频率依赖性.并根据宏畴一微畴转变理论探讨了该体系陶瓷产生介电弛豫的机理.     

Bi(Mg_(1/2)Ti_(1/2))O_3-PbTiO_3压电陶瓷体系介电与居里温度特性研究

采用传统固相法工艺制备了(1-x)Bi(Mg1/2Ti1/2)O3-x Pb Ti O3(BMT-x PT,0.34≤x≤0.44)陶瓷。研究发现,随着PT含量增加,试样结构由三方相逐渐转变为四方相结构,当0.36x0.40时,试样结构处于准同型相界(MPB)区。研究表明BMT组元是一种具有非铁电体特征的组分,随着PT含量减少,BMT-PT体系的居里温度减小,介电峰变得越来越不明显。通过研究BMT-PT体系组分与居里温度(TC)的关系可以看出:(1)PT含量为0.34~0.44时,TC随BMT含量变化实验值和Stringer的经验值差异较小,变化趋势一致;(2)BMT-PT体系居里温度最大值可能在x=0.73的附近,其居里温度最大值TC max约为550℃。     

Dielectric response of Sb-doped CaCu3Ti4O12 ceramics

A series of Sb-doped CaCu₃Ti₄O₁₂ ceramics were fabricated by the conventional solid state method, and their crystalline structures, microstructures and dielectric properties were investigated systematically. All the ceramic samples exhibited perovskite-related structures in space group Im $\bar{3}$ . The grain size decreased slightly as Sb concentration increased; whereas the dielectric permittivity of the ceramics increased slightly. The giant dielectric response was considered to be closely related with a reduction in the potential barrier height at grain boundaries (GBs). The activation energy for the dc conduction process is comparable to that for conduction at GBs, indicating that the dc conduction process is associated with the electrical response of GBs.     

Low-temperature sintered (Zn0.65Mg0.35)TiO3 microwave ceramics doped with CuV2O6

The influence of the CuV₂O₆ additives on the densification, microstructural evolution, and dielectric properties of (ZnMg)TiO₃ (ZMT) ceramics was investigated. The sintering agent CuV₂O₆ can significantly enhance the sinterability and lower the firing temperature of ZMT dielectrics to ≤930 °C. SEM shows that liquid phase sintering induced by CuV₂O₆ can promote the grain growth and elevate the bulk density dramatically. XRD indicates that excess CuV₂O₆ beyond the solubility ~1.5 wt% could form the secondary phase and affect the crystalline structure. The microwave results show that the dielectric constant (ε_r) increases gradually, but the quality factor (Q × f) and the temperature coefficients of resonant frequency (τ_f) decrease with increasing CuV₂O₆ content. Moreover, TiO₂ addition can effectively improve the microwave properties of CuV₂O₆-doped ZMT dielectrics and especially compensate the negative τ _f. (Zn_0.65Mg_0.35)TiO₃ ceramics codoped with 1 wt% CuV₂O₆ and 9 wt% TiO₂ sintered at 930 °C exhibited the optimum microwave dielectric properties: ε _r = 26.2, Q × f = 31,930 GHz, τ _f ≈ −0.32 × 10⁻⁶/°C.     

Dielectric and ferroelectric properties of Bi(Zn1/2Ti1/2)O3-PbTiO3-PbZrO3 ternary ceramics

Ceramics of a new ternary solid solution system, xBi(Zn(1/2)Ti(1/2))O(3-yPbTiO(3)z)PbZrO(3) (xBZT-yPT-zPZ), with compositions along the solubility limit curve are prepared by solid-state reaction and sintering technique. Two morphotropic phase boundaries (MPBs) separating the orthorhombic and tetragonal (MPB(O-T)) phases and the tetragonal and rhombohedral (MPB(T-R)) phases, respectively, are observed with increasing z (0.10 ≤ x ≤ 0.21; 0 ≤ y ≤ 0.49). It is found that the transition from the ferroelectric to paraelectric phase becomes more diffuse with the addition of BZT into the PZT solid solution. Enhanced dielectric and ferroelectric properties appear at MPB(R-T), which exists over a wide composition region (0.45 ≤ z ≤ 0.6), as revealed by X-ray diffraction and dielectric measurements. The dielectric constant reaches a maximum value (ε' = 1250) on the tetragonal majority side of the MPB. The highest remnant polarization (P(r) = 34.2 μC/cm(2)) is found in the composition at the center of the MPB, where the rhombohedral and tetragonal phases coexist in almost equal quantities.     

纳米K2Ti6O13W合成中的形态演化和生长机理

以纳米TiO2为原料,通过煅烧反应制备了纳米K2Ti6O13晶须,对晶须合成中温度和时间诱导的相变、形态演化和生长机理等进行了原位研究.结果表明:纳米TiO2作原料可显著降低晶须合成温度,适宜的煅烧温度为900～1100℃.形态演化观察和高温XRD分析表明:K2Ti6O13晶须的相变及生长对温度极为敏感,形态演化是基于初期爆发式的相变和随后串并联式的长大.K2Ti6O13晶须的生长遵守本研究提出的串并联机制,晶须轴向的生长台阶是串并联生长的直接结果.