Preparation and electrochemical behavior of methylene blue intercalated into layered niobate K<Subscript>4</Subscript>Nb<Subscript>6</Subscript>O<Subscript>17</Subscript>

K₄Nb₆O₁₇ nano-layered compound was obtained by solid-phase synthesis and then methylene blue (MB) was intercalated into layered niobate K₄Nb₆O₁₇ interlayer I by a two-step guest-guest exchange method using the intercalation compound, methyl viologen (MV²⁺)–K₄Nb₆O₁₇, as precursor. The optically transparent MB⁺–K₄Nb₆O₁₇ nanocomposite thin film has been characterized by XRD, IR, TGA, elemental analysis, UV, and electrochemical measurements. It was estimated that the intercalated MB⁺ ions are mainly aggregated. The cyclic voltammogram of the MB⁺–K₄Nb₆O₁₇ nanocomposite thin film exhibited a fine diffusion-controlled cathodic process, which hints the possibility of being utilized as an electrode modifying material.     

Preparation of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript>/TiO<Subscript>2</Subscript> bio-ceramic on titanium substrate by micro-arc oxidation

K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings are prepared successfully by micro-arc oxidation on titanium substrate in pure KOH electrolyte solution. The coating is prepared at various applied current density (150–500 mA/cm²) and in KOH electrolyte with different concentrations (0.5–1.2 mol/L). The composition and surface morphologies of coatings are strongly dependent on the applied current density and the electrolyte concentration. On the condition of lower current density and electrolyte concentration, K₂Ti₆O₁₃ phase almost cannot be formed. The phase is mainly composed of rutile and K₂Ti₆O₁₃ with increasing current density and electrolyte concentration. The surface morphologies are composed of whiskers and porous structures. The ability of K₂Ti₆O₁₃/TiO₂ bio-ceramic films inducing apatite deposition is evaluated by soaking it in biological model fluids. The results show the K₂Ti₆O₁₃/TiO₂ bio-ceramic coatings possess excellent capability of inducing bone-like apatite to deposit.     

Ag-decorated octahedral K<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>6</Subscript> nanoparticles with enhanced photocatalytic performance

The Ag-K₂Nb₂O₆ nanocomposites are synthesized by a two-step method where the octahedral K₂Nb₂O₆ is initially prepared by solvothermal reaction and then the Ag particles are anchored onto the surface of K₂Nb₂O₆ through the photoreduction of AgNO₃. The XRD, SEM, TEM, XPS, DRS are applied to characterize the structure, morphology and optical properties, which confirm that the Ag particles are successfully deposited on the surface of K₂Nb₂O₆. Compared with the pure K₂Nb₂O₆, the Ag modified K₂Nb₂O₆ catalysts show an obvious enhancement catalysis under UV–Vis light, because that could efficiently promote the light absorption and the separation of photoelectrons and holes.     

Electroluminescence of (Pb<Subscript>0.91</Subscript>La<Subscript>0.09</Subscript>)(Zr<Subscript>0.65</Subscript>Ti<Subscript>0.35</Subscript>)O<Subscript>3</Subscript> ceramics with nanopolar structure

Lanthanum-doped lead zirconate titanate (PLZT) relaxor ceramics with (Pb_0.91La_0.09)(Zr_0.65Ti_0.35)O₃ composition exhibits a repolarization-induced electroluminescence (EL) with a pronounced discrete character of emission. It is established that this behavior is related to the reorientation of nanodimensional polar regions in a strong pulsed electric field in the vicinity of a smeared phase transition. The temporal and temperature dependences of the EL intensity have been studied.     

Influence of A-site magnesium doping on structural and electrical properties of BaZr<Subscript>0.1</Subscript>Ti<Subscript>0.9</Subscript>O<Subscript>3</Subscript> ceramics

The effects of the replacement of Ba²⁺ by off-center Mg²⁺ ions on the structural and electrical properties of BaZr_0.1Ti_0.9O₃ ceramics were investigated. We show that the use of magnesium as A-site dopant favors the formation of the perovskite phase at a lower temperature and improves the densification of the ceramics. Combining XRD, SEM and electrical measurements, we determined that the solubility limit of Mg is ~ 2%. We show that Mg doping leads to a decrease in both the Curie temperature and remnant polarization of the ceramics. A 1% Mg content, however, enhances the room-temperature d₃₃ piezoelectric coefficient due to the composition proximity to an impurity induced morphotropic phase boundary.     

Splitting behavior and structural transformation process of K<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>13</Subscript> whiskers under hydrothermal conditions

The splitting behavior and structural transformation process of K₂Ti₆O₁₃ whiskers in various hydrothermal solutions were investigated by the X-ray diffraction technique, scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. TiO₂ (B) particle aggregates and rutile twinned crystals were produced respectively in diluted and concentrated HCl solutions via “dissolution-precipitation” mechanism, while no changes were observed in deionized water. In contrary to the chemical inertia of K₂Ti₆O₁₃ whiskers in KOH solution, trititanate nanowires were synthesized by splitting the bulk K₂Ti₆O₁₃ whiskers in NaOH solution. The driving force for the formation of nanowires originated from the intrinsic strain induced by the phase transition from K₂Ti₆O₁₃ with a tunnel structure to layered trititanate. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Nanocrystalline PbIn<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> ceramics and its properties

A ferroelectric relaxor PbIn_0.5Nb_0.5O₃ (PIN) ceramics has been obtained using a modified ceramic technology, with the sintering stage preceded by compression and shear straining of the synthesized charge in Bridgman anvils. The dimensions of ceramic grains after this pretreatment are spread over a range from 100 to 1250 nm. A comparative investigation of the properties of PIN ceramics obtained using the standard and modified technology showed that the proposed mechanical action at the charge preparation stage can be used for controlled modification of the properties of ferroelectric ceramics.     

Synthesis,dielectric, and hysteresis behaviour of Ba(Nb<Subscript>0.2</Subscript>Ti<Subscript>0.8</Subscript>)O<Subscript>3</Subscript> ceramics and their solid solutions with BaZrO<Subscript>3</Subscript>

Solid state reaction technique was employed to synthesize Ba(Nb_0.2Ti_0.8)O₃ [BNT], and 0.9Ba(Nb_0.2Ti_0.8)O₃ + 0.1BaZrO₃ [BNT + BZ] samples. Sintered pellets were investigated for its dielectric (ε_r and tanδ) properties in the temperature range 100 K–380 K and in the frequency range of 100 Hz–1 MHz. The variation of ε_r and tan δ may be attributed to hopping of trapped charge carriers, which resulted in an extra dielectric response in addition to the dipole response. Hysteresis loop measurements were studied in the temperature regime 295 K–423 K. Loop area shrunk with the increase of temperature that may be due to phase transition from ferroelectric to paraelectric state.     

Ab initio study on fracture toughness of Ti<Subscript>0.75</Subscript>X<Subscript>0.25</Subscript>C ceramics

Ab initio density functional theory calculations have been performed to evaluate the fracture toughness for selected Ti_0.75X_0.25C ceramics (X = Ta, W, Mo, Nb and V). The calculated Young’s modulus E, surface energy γ and fracture toughness K _IC of pure TiC are in a good agreement with experimental data and other theoretical calculations. The results for Ti_0.75X_0.25C system show that alloying additions increase Young’s modulus, and all but vanadium increase surface energy. It was observed that tungsten has the most significant effect on increasing Young’s modulus, while tantalum on increasing surface energy of the Ti_0.75X_0.25C system. Surface energy plays a dominated role in determining the trend of fracture toughness. Overall, tantalum and tungsten are the most effective alloying elements in increasing the fracture toughness of Ti_0.75X_0.25C ceramics.     

Dielectric and a.c. conductivity studies in pure and manganese doped layered K<Subscript>2</Subscript>Ti<Subscript>4</Subscript>O<Subscript>9</Subscript> ceramics

The results of a.c. electrical conductivity studies have been reported on pure K₂Ti₄O₉ (named PT) and its 1.0 molar percentage of MnO₂ doped derivative (named MPT) ceramics in the temperature range 373–898 K. Four regions have been identified in the log(σ_a.c. T) versus 1000/T plots. Conduction in the lowest temperature region I is attributed to the mixed exchangeable interlayer ionic and electronic hopping (polaron) conduction. A dielectric loss peak with distribution of relaxation times perturbs the conduction in next regions II and III. However, in region III for both the samples non-relaxor ferroelectric property may be proposed. The modified interlayer ionic conduction has been proposed towards the higher temperature region IV. Loss tangent (tan δ) versus frequency and dielectric constant (ε) versus frequency plots at different temperatures have also been given for both the samples. The results of tan δ versus temperature and ε versus temperature at different frequencies have further been reported for both of the above compounds in this paper.     

Synthesis of anisometric KSr<Subscript>2</Subscript>Nb<Subscript>5</Subscript>O<Subscript>15</Subscript> particles in the SrNb<Subscript>2</Subscript>O<Subscript>6</Subscript>–Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>–KCl system

Anisometric and agglomerate-free template particles are important for fabrication of grain-oriented ceramics. In the present work, preparation of acicular KSr₂Nb₅O₁₅ (KSN) particles was firstly explored in the SrNb₂O₆–Nb₂O₅–KCl system by molten salt synthesis (MSS) method. It was found that the molar ratio of SrNb₂O₆ to Nb₂O₅, the amount of KCl salt and synthesis time could significantly affect the phase structure and morphology of KSN particles. When calcined at 1,150 °C for 6 h with the molar ratio of SrNb₂O₆ to Nb₂O₅ was 1 and the weight ratio of salt to oxide source was 1.50, pure KSN particles with well-developed acicular morphology were successfully obtained in this system. They were agglomerate-free and with proper scale in the size range of 5–30 μm, which made them the ideal templates for fabricating textured ceramics. In addition, some new reaction and growth mechanisms were proposed in this work.     

Dielectric and piezoelectric properties of MnO<Subscript>2</Subscript>-doped K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>Nb<Subscript>0.92</Subscript>Sb<Subscript>0.08</Subscript>O<Subscript>3</Subscript> lead-free ceramics

Lead-free MnO₂-doped K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramics have been fabricated by a conventional ceramic technique and their dielectric and piezoelectric properties have been studied. Our results show that a small amount of MnO₂ (0.5–1.0 mol%) is enough to improve the densification of the ceramics and decrease the sintering temperature of the ceramics. The co-effects of MnO₂ doping and Sb-substitution lead to significant improvements in the ferroelectric and piezoelectric properties. The K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramic with 0.5 mol%MnO₂ doping possesses optimum propeties: d ₃₃ = 187 pC/N, k _P = 47.2%, ε _r = 980, tanδ = 2.71% and T _c = 287 °C. Due to high tetragonal-orthorhombic phase transition temperature (T _O-T ~ 150 °C), the K_0.5Na_0.5Nb_0.92Sb_0.08O₃ ceramic with 0.5 mol%MnO₂ doping exhibits a good thermal stability of piezoelectric properties.     

Crystal structure and electrical properties of CaNaBi<Subscript>2</Subscript>Nb<Subscript>3</Subscript>O<Subscript>12</Subscript> ceramics

Monophasic CaNaBi₂Nb₃O₁₂ powders were synthesized via the conventional solid-state reaction route. Rietveld refinement of the X-ray powder diffraction (XRD) data and selected area electron diffraction (SAED) studies confirmed the phase to be a three-layer Aurivillius oxide associated with an orthorhombic B2cb space group. The dielectric properties of the ceramics have been studied in the 300–800 K temperature range at various frequencies (1 kHz to 1 MHz). A dielectric anomaly was observed at 676 K for all the frequencies corresponding to the ferroelectric to paraelectric phase transition as it was also corroborated by the high temperature X-ray diffraction studies. The incidence of the polarization–electric field (P vs. E) hysteresis loop demonstrated CaNaBi₂Nb₃O₁₂ to be ferroelectric.     

PTCR effect in BaBi<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>9</Subscript>-doped BaTiO<Subscript>3</Subscript> ceramics

The influences of BaBi₂Nb₂O₉ content on the electrical property and the microstructure of BaTiO₃-based materials have been studied. With an increase in BaBi₂Nb₂O₉ content the grain size decreases. All the prepared BaBi₂Nb₂O₉ doping BaTiO₃-based thermistors show typical PTC effect. As the amount of BaBi₂Nb₂O₉ added in BaTiO₃-based ceramics increases, resistivity appears to exhibit a minimum value. At high BaBi₂Nb₂O₉ content (≥0.0875), the resistivity increased again with increasing BaBi₂Nb₂O₉ content. At a given content of BaBi₂Nb₂O₉, the influence of sintering temperature on the electrical properties of samples has been investigated. A minimum of room temperature resistivity is obtained at the sintering temperature equal to 1,290 °C at a given content of BaBi₂Nb₂O₉.     

Properties of fluorine-doped PbMg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>O<Subscript>3</Subscript> ceramics

We report the first fluorine doping of lead magnesium niobate in the PbMg _{(1 + x)/3}Nb_{(2 ? x)/3}O_{3 ? x} F _x system in a wide composition range, x = 0.025 to 0.625. The fluorine content of the samples is shown to be substantially lower than the intended one because of the fluorine volatilization in the form of HF during synthesis and sintering in air. The ceramics consist of magnesium and lead oxides undetectable by x-ray diffraction, and a perovskite phase whose composition can be represented by the formula PbMg_{(1 + m)/3}Nb_{(2 ? m)/3}O_{3 ? m} F _m , where the fluorine content after sintering is m ≤ 0.12. The PbO and MgO contents of the ceramics depend on the starting mixture composition (x) and heat-treatment conditions (hydrogen fluoride and lead oxide volatilization). As a result of the low fluorine content, the diffraction patterns of the samples show no superlattice reflections, and their lattice parameter varies insignificantly with x. Data are presented on the temperaturedependent dielectric permittivity of ceramic samples sintered and annealed under different conditions.     

Electric properties of Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript>(BIT)–CaCu<Subscript>3</Subscript>Ti<Subscript>4</Subscript>O<Subscript>12</Subscript> (CCTO) composite substrates for high dielectric constant devices

A study of the effect of the presence of BIT (Bi₄Ti₃O₁₂) in the dielectric and optical properties of the CaCu₃Ti₄O₁₂ (CCTO) is presented. The samples were prepared by the solid state procedure. Mechanical alloying followed by the solid state procedure has been used successfully to produce powders of CaCu₃Ti₄O₁₂ (CCTO) and BIT (Bi₄Ti₃O₁₂) to be used in the composites. We also look at the effect of the grain size of the BIT and CCTO in the final properties of the composite. The samples were studied using X-Ray diffraction, scanning electron microscopy (SEM), Raman and infrared spectroscopy. We also did a study of the dielectric function K and dielectric loss of the samples. The role played by the grain size of CCTO and BIT in the dielectric constant and structural properties of the substrates are discussed. For frequencies below 10 MHz the K value presented by the CCTO100 sample is always higher than the K value presented by the BIT100 sample. At 100 Hz the value of K 1900 for the CCTO100 sample and 288 for the BIT100 sample. However for the composite sample one has an unexpected result. The dielectric constant is higher for all the frequencies under study. At 100 Hz the value of the K is around 10.000 for the BIT10 sample. Which is more than one order bigger compared to the CCTO100 value for the same frequency. Therefore, these measurements confirm the potential use of such materials for small high dielectric planar devices. These composites are also attractive for capacitor applications and certainly for microelectronics, microwave devices (cell mobile phones for example), where the miniaturization of the devices is crucial.     

Structure and electrical properties of MnO doped (Ba<Subscript>0.96</Subscript>Ca<Subscript>0.04</Subscript>)(Ti<Subscript>0.92</Subscript>Sn<Subscript>0.08</Subscript>)O<Subscript>3</Subscript> lead free ceramics

In this work, (Ba_0.96Ca_0.04)(Ti_0.92Sn_0.08)O₃–xmol MnO (BCTS–xMn) lead-free piezoelectric ceramics were fabricated by the conventional solid-state technique. The composition dependence (0 ≤ x ≤ 3.0 %) of the microstructure, phase structure, and electrical properties was systematically investigated. An O–T phase structure was obtained in all ceramics, and the sintering behavior of the BCTS ceramics was gradually improved by doping MnO content. In addition, the relationship between poling temperature and piezoelectric activity was discussed. The ceramics with x = 1.5 % sintering at temperature of 1330 °C demonstrated an optimum electrical behavior: d ₃₃ ~ 475 pC/N, k _p ~ 50 %, ε _r ~ 4060, tanδ ~ 0.4 %, P _r ~ 10.3 μC/cm², E _c ~ 1.35 kV/mm, T _C ~ 82 °C, strain ~0.114 % and \(d_{33}^{*}\) ~ 525 pm/V. As a result, we achieved a preferable electric performance in BaTiO₃-based ceramics with lower sintering temperature, suggesting that the BCTS–xMn material system is a promising candidate for lead-free piezoelectric ceramics.     

The Multiferroic Properties of (Bi<Subscript>0.9</Subscript>Ba<Subscript>0.1</Subscript>)(Fe<Subscript>0.95</Subscript>Mn<Subscript>0.05</Subscript>)O<Subscript>3</Subscript> Films

(Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ films were prepared on LaNiO₃-coated surface oxidized Si substrates. XRD and Raman measurements confirm that the (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ film has pure R3c structure. Clear ferromagnetism with saturated magnetization of about 25 emu/cm³ has been observed at room temperature. The ferroelectric properties of the (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ film was confirmed by the observation of the ferroelectric domains and the converse piezoelectric coefficient d ₃₃ versus applied voltage hysteresis loops by piezoelectric force microscopy (PFM). The observation of ferromagnetism and ferroelectricity in (Bi_0.9Ba_0.1)(Fe_0.95Mn_0.05)O₃ films indicates the potential multiferroic applications.