Modelling,structural, thermal,optical and vibrational studies of a new organic–inorganic hybrid material (C<Subscript>5</Subscript>H<Subscript>16</Subscript>N<Subscript>2</Subscript>)Cd<Subscript>1.5</Subscript>Cl<Subscript>5</Subscript>

Chemical preparation, theoretical calculations, X-ray single-crystal diffraction, thermal analysis, electrochemical measurements, IR, Raman and UV spectroscopic investigations of a novel organic–inorganic hybrid material (C₅H₁₆N₂)Cd_1.5Cl₅ are described. The structure provides a new interesting example of infinite inorganic chains of [Cd_1.5Cl₅]\(_{\mathbf {n}}^{\boldsymbol {2\mathrm {n}-}}\) following the a crystallographic direction. The [Cd_1.5Cl₅]^2? anions are interconnected by N–H ? Cl hydrogen bonds. The Hirshfeld surface and associated fingerprint plots of the compound are presented to explore the nature of intermolecular interactions and their relative contributions in building the solid-state architecture. IR and Raman spectra are reported and discussed on the basis of group theoretical analysis and quantum chemical density functional theory (DFT) calculation. The molecular HOMO–LUMO compositions and their respective energy gaps are also drawn to explain the activity of our compound. Thermal analysis reveals the anhydrous character of the compound.     

The effect of Fe contents on the local structure and crystallization behavior of SiO<Subscript>2</Subscript>–CaO–P<Subscript>2</Subscript>O<Subscript>5</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

The glass and glass ceramics containing SiO₂–CaO–Fe₂O₃–P₂O₅ were prepared by sol–gel method. The influence of the Fe contents on the crystallization and local structure of the glass and glass ceramics was systematically investigated. The crystal structure of the glass ceramics was identified by XRD characterization. Hematite phase can be precipitated from the glass matrix in all glass ceramics with various Fe contents, and the crystallographic parameters of hematite were determined by XRD Rietveld refinement. The crystallization kinetics of the glasses was investigated in detail. Relative low activation energies were obtained at low Fe contents. The local structure evolution of the glass and glass ceramics has been studied in-depth by means of FTIR and Mössbauer spectroscopy. Fe element is present both as network former and network modifier which significantly influenced the crystallization activation energies of the glasses. The results of this work may be of great significance for the material design and practical applications of bioactive magnetic glass ceramics for hyperthermia.     

Crystal structure and properties of BaTiO<Subscript>3</Subscript>–(Bi<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)TiO<Subscript>3</Subscript> ceramic system

(1 − x)BaTiO₃–x(Bi_0.5Na_0.5)TiO₃ (x ranged from 0.01 to 0.96) ceramics were fabricated by the conventional ceramic technique. The crystal structure, as well as dielectric and piezoelectric properties of the ceramics were studied. All the ceramics formed single-phase solid solutions with perovskite structure after sintering in air at 1150–1250 °C for 2–4 h. The crystal structure and microstructure varied gradually with the increase of (Bi_0.5Na_0.5)TiO₃ (BNT) content. The Curie temperature, T _c, shifted monotonously to high temperature as BNT increased. The ceramics with 20–90 mol% BNT had relatively low and stable dielectric loss characteristics. The piezoelectric constant, d ₃₃, enhanced with the increase of BNT content through a maximum value in a composition of 93 mol% BNT and then tended to decrease. The maximum value, 148 pC/N, of piezoelectric constant d ₃₃ together with the electromechanical coupling factors, k _t, 19.8% and k _p, 15.8%, were obtained when BNT was 93 mol%.     

Effects of LiNbO<Subscript>3</Subscript> doping on the microstructures and electrical properties of BiScO<Subscript>3</Subscript>–PbTiO<Subscript>3</Subscript> piezoelectric system

Piezoelectric ceramics xLiNbO₃–yBiScO₃–(1?x?y)PbTiO₃ (LN–BS–PT, 0.00?≤?x?≤?0.10, 0.30?≤?y?≤?0.36) were synthesized and their phase diagram and morphotropic phase boundary between rhombohedral and tetragonal phases have been confirmed. The optimal properties were found at the composition of 0.03LN–0.36BS–0.61PT with piezoelectric coefficient d₃₃^* value of 702 pm/V, d₃₃ of 551 pC/N, planar electromechanical coupling factor k_p of 0.51, remnant polarization P_r of 46.5 µC/cm², Curie temperature T_c of 337 °C, and a large strain of 0.351% at an electric field of 50 kV/cm and frequency of 2 Hz with a low strain hysteresis of 5.9%. The Curie temperature of the ternary system presents a linear relationship with LiNbO₃ and BiScO₃ contents. The optimization of these electric properties was probably ascribed to the enhancement in domain walls and the improving mobility of domain switching due to LiNbO₃ doping.     

Preparation,structure and microwave dielectric properties of 3MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–3TiO<Subscript>2</Subscript> ceramics

3MgO–Al₂O₃–3TiO₂ (MAT) ceramics were prepared by a conventional solid-state reaction method. The crystal structure, sintering behavior and microwave dielectric properties of ceramics were investigated using X-ray diffraction, scanning electron microscopy and network analyzer. MAT ceramics contained the coexistence of three phases, including MgAl₂O₄, MgTiO₃ and MgTi₂O₅. The ceramics sintered at 1350 °C for 4 h presented excellent comprehensive performances with relative permittivity (ε _r ) of 15.4, quality factor (Q × f) of 91,000 GHz and temperature coefficient of resonant frequency (τ _f ) about ?55.1 ppm/°C.     

Structure,electrical, and optical properties of ZnO-substituted PbO for the Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O glass system

Glasses of the 0.5Er³⁺/2.5Yb³⁺ co-doped (40Bi₂O₃–20GeO₂–(30 − x)PbO–xZnO–10Na₂O system where x = 0.0, 5, 10, 15, 20, 25, and 30 mol%) have been characterized by FT-IR spectroscopy measurements to obtain information about the influence of ZnO-substituted PbO on the local structure of the glass matrix. The density and the molar volume have been determined. The influences of the ZnO-substituted PbO on the structure of glasses have been discussed. The dc conductivity measured in the temperature range 475–700 K obeys Arrhenius law. The conductivity decreases while the activation energy for conduction increases with increase ZnO content. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400–1100 nm. The values of the optical band gap E _opt for all types of electronic transitions and refractive index have been determined and discussed. The real and imaginary parts ε₁ and ε₂ of dielectric constant have been determined.     

Effect of the ZrO<Subscript>2</Subscript> concentration on the crystallization behavior and the mechanical properties of high-strength MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript> glass–ceramics

High-strength, colorless glass–ceramics in the MgO/Al₂O₃/SiO₂ system with high concentrations of ZrO₂ and a great potential for technical application, e.g., as high-performance hard disc substrates, are investigated. ZrO₂ concentrations from 6 to 9 mol% are added to a stoichiometric cordierite glass to investigate the influence of the concentration of the nucleating agent on the crystallization behavior and the mechanical properties. The phase formation and the microstructure of the glass–ceramics are studied using X-ray diffraction and scanning electron microscopy including electron backscatter diffraction. It is shown that the volume crystallization of ZrO₂, a low-/high-quartz solid solution (low-/high-QSS), and spinel is accompanied by the surface crystallization of indialite. This phase offers a much smaller coefficient of thermal expansion than the other crystal phases, which may induce high compressive stresses in the surface layer of the glass–ceramics after cooling and seems to result in excellent mechanical properties of the material. Biaxial flexural strengths of up to 1 GPa were measured. Higher ZrO₂ concentrations reduce the surface crystallization of indialite and decrease the mean size of the crystals resulting in a higher translucency. The volume-crystallizing phases and the mechanical properties of the glass–ceramics do not seem to be significantly affected by the analyzed ZrO₂ concentrations.     

Structure and piezoelectric properties of new ternary K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>NbO<Subscript>3</Subscript>–LiSbO<Subscript>3</Subscript>–CaTiO<Subscript>3</Subscript> lead-free piezoceramics

New ternary (1−x)K_0.5Na_0.5NbO₃–x(0.80LiSbO₃–0.20CaTiO₃) lead-free ceramics were fabricated by a conventional ceramic technique and their structure and piezoelectric properties were studied. The results of X-ray diffraction reveal that LiSbO₃ and CaTiO₃ diffuse into the K_0.5Na_0.5NbO₃ lattices to form a new solid solution with a perovskite structure. After the addition of LiSbO₃ and CaTiO₃, the cubic-tetragonal and tetragonal-orthorhombic phase transitions shift to lower temperatures. Coexistence of the orthorhombic and tetragonal phases is hence formed in the ceramics with 0.03 < x < 0.07 at room temperature, leading to a significant enhancement of the piezoelectric properties. For the ceramics with x = 0.04–0.06, the piezoelectric properties become optimum: d ₃₃ = 172–253 pC/N, k _P = 49.9–55.5%, k _t = 49.2–52.1% and T _C = 348–373 °C. The ceramic with x = 0.04 also exhibits a good thermal stability of piezoelectric properties.     

Ferroelectric and piezoelectric properties of new NaNbO<Subscript>3</Subscript>–Bi<Subscript>0.5</Subscript>K<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> lead-free ceramics

New lead-free ceramics (1–x)NaNbO₃–xBi_0.5K_0.5TiO₃ have been fabricated by the conventional ceramic sintering technique, and their ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction reveal that Bi_0.5K_0.5TiO₃ diffuses into the NaNbO₃ lattices to form a new perovskite-type solid solution with orthorhombic symmetry. The addition of a small amount of Bi_0.5K_0.5TiO₃ (x ≥ 0.025) transforms the ceramics from antiferroelectric to ferroelectric. The ceramic with x = 0.10 possesses the largest remanent polarization P _r and thus exhibits the optimum piezoelectric properties, giving d ₃₃ = 71 pC/N, k _p = 16.6% and k _t = 39.7%. The ceramics with low doping level of Bi_0.5K_0.5TiO₃ are normal ferroelectrics and the ferroelectric-paraelectric phase transition becomes diffusive gradually with the doping level x of Bi_0.5K_0.5TiO₃ increasing. Our results show the (1–x)NaNbO₃–xBi_0.5K_0.5TiO₃ ceramics is one of the good candidates for lead-free piezoelectric and ferroelectric materials.     

Synthesis,microstructure, and electrical behavior of (Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>)<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>TiO<Subscript>3</Subscript> piezoelectric ceramics via a citric acid sol–gel method

Nanosize (Na_0.5Bi_0.5)_0.94Ba_0.06TiO₃ precursor powders were prepared via the citric acid sol–gel method. The ceramics were sintered at 1100–1150 °C. All ceramics exhibit a single-phase perovskite structure. With increasing sintering temperature, the average size of grains in the samples changes slightly from 0.3 to 0.5 µm. All ceramics show obvious dielectric dispersion. Activation energy values were obtained via impedance, electric modulus, and conductivity, respectively, which are in the range of 0.60–1.06 eV. Compared to ceramics synthesized by solid-state reaction method, the as-synthesized samples are fine-grained and have high depolarization temperature and excellent temperature stability of the piezoelectric constant (d ₃₃). The d ₃₃ value of the sample sintered at 1120 °C remains as high as 119 pC N^?1 with increasing annealing temperature to 115 °C, whereas the reduced amplitude of d ₃₃ is only approximately 3%.     

In vitro dissolution behavior of SiO<Subscript>2</Subscript>–MgO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–K<Subscript>2</Subscript>O–B<Subscript>2</Subscript>O<Subscript>3</Subscript>–F glass–ceramic system

Herein, we report the results of the in vitro dissolution tests, which were carried out by immersing the selected glass-ceramic samples in artificial saliva (AS) for various time periods of up to 42 days. In our experiments, the SiO(2)-MgO-Al(2)O(3)-K(2)O-B(2)O(3)-F glass ceramics with different crystal morphology and crystal content were used and a comparison is also made with the baseline glass samples (without any crystals). The bioactivity of the samples was probed by measuring the changes in pH, ionic conductivity and ionic concentration of AS following in vitro dissolution experiments. High resistance of the selected glass-ceramic samples against in vitro leaching has been demonstrated by minimal weight loss (<1%) and insignificant density change, even after 6 weeks of dissolution in artificial saliva. While XRD analysis reveals the change in surface texture of the crystalline phase, FT-IR analysis weakly indicated the Ca-P compound formation on the leached surface. The experimental measurements further indicate that the leaching of F(-), Mg(2+) ions from the sample surface commonly causes the change in the surface chemistry. Furthermore, the presence of (Ca, P, O)-rich mineralized deposits on the leached glass-ceramic surface as well as the decrease in Ca(2+) ion concentrations in the leaching solutions (compared to that in the initial AS solution) provide evidences of the moderate bioactive or mild biomineralisation behaviour of investigated glass-ceramics.     

Compositional dependence of the structural and dielectric properties of Li<Subscript>2</Subscript>O–GeO<Subscript>2</Subscript>–ZnO–Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> glasses

(10Li₂O–20GeO₂–30ZnO–(40-x)Bi₂O₃–xFe₂O₃ where x = 0.0, 3, 6, and 9 mol%) glasses were prepared. A number of studies, viz. density, differential thermal analysis, FT-IR spectra, DC and AC conductivities, and dielectric properties (constant ε′, loss tan δ, AC conductivity, σ _ac, over a wide range of frequency and temperature) of these glasses were carried out as a function of iron ion concentration. The analysis of the results indicate that, the density and molar volume decrease with an increasing of iron content indicates structural changes of the glass matrix. The glass transition temperature T _g and onset of crystallization temperature T _x increase with the variation of concentration of Fe₂O₃ referred to the growth in the network connectivity in this concentration range, while glass-forming ability parameter ΔT decrease with increase Fe₂O₃ content, indicates an increasing concentration of iron ions that take part in the network-modifying positions. The FT-IR spectra evidenced that the main structural units are BiO₃, BiO₆, ZnO₄, GeO₄, and GeO₆. The structural changes observed by varying the Fe₂O₃ content in these glasses and evidenced by FTIR investigation suggest that the iron ions play a network modifier role in these glasses while Bi₂O₃, GeO₂, and ZnO play the role of network formers. The temperature dependence of DC and AC conductivities at different frequencies was analyzed using Mott’s small polaron hopping model and, the high temperature activation energies have been estimated and discussed. The dielectric constant and dielectric loss increased with increase in temperature and Fe₂O₃ content.     

Effect of gamma radiation on electrical and optical properties of (TeO<Subscript>2</Subscript>)<Subscript>0·9</Subscript> (In<Subscript>2</Subscript>O<Subscript>3</Subscript>)<Subscript>0·1</Subscript> thin films

We have studied in detail the gamma radiation induced changes in the electrical properties of the (TeO₂)_0·9 (In₂O₃)_0·1 thin films of different thicknesses, prepared by thermal evaporation in vacuum. The current–voltage characteristics for the as-deposited and exposed thin films were analysed to obtain current versus dose plots at different applied voltages. These plots clearly show that the current increases quite linearly with the radiation dose over a wide range and that the range of doses is higher for the thicker films. Beyond certain dose (a quantity dependent on the film thickness), however, the current has been observed to decrease. In order to understand the dose dependence of the current, we analysed the optical absorption spectra for the as-deposited and exposed thin films to obtain the dose dependences of the optical bandgap and energy width of band tails of the localized states. The increase of the current with the gamma radiation dose may be attributed partly to the healing effect and partly to the lowering of the optical bandgap. Attempts are on to understand the decrease in the current at higher doses. Employing dose dependence of the current, some real-time gamma radiation dosimeters have been prepared, which have been found to possess sensitivity in the range 5–55 μGy/μA/cm². These values are far superior to any presently available real-time gamma radiation dosimeter.     

Optical properties and crystallization of glasses in the system Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–MoO<Subscript>3</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The purpose of this work is to study the optical properties and crystallization of glasses in the ternary system Bi₂O₃–MoO₃–B₂O₃. In order to verify the obtaining of bismuth borate crystal phases several glass compositions have been selected for crystallization. The obtained samples were characterized by X-ray diffraction, scanning electron microscopy and UV–Vis spectroscopy. The UV–Vis spectroscopy showed that the obtained glasses are transparent in the visible region. The values of optical band gap (E _opt) and changes in cut-off (λ_c) depending on composition are reported. It was established that the increase in the MoO₃ content led to decreasing the transmittance of the glasses. Moreover, the absorption edge shifts towards longer wavelength.     

Thermal and dielectric properties of the LTCC composites based on the eutectic system BaO–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The low-temperature co-fired ceramic (LTCC) composites containing quartz based on the eutectic system BaO–Al₂O₃–SiO₂–B₂O₃ are fabricated at the sintering temperature below 980 °C. Preparation process and sintering mechanism were described and discussed, respectively. The results indicated that the addition of quartz to the eutectic system can availably improve dielectric properties of the LTCC composites. In addition, The LTCC composites with optimum compositions, which were obtained by the regulation of an Al₂O₃ content in the composite, can express excellent dielectric properties (permittivity: 5.94, 5.48; loss: 7 × 10⁻⁴, 5 × 10⁻⁴), considerable CTE values (11.7 ppm. °C⁻¹, 10.6 ppm. °C⁻¹) and good mechanical properties (128 MPa,133 MPa).     

Structural and electrical properties of Bi<Subscript>1/2</Subscript>Na<Subscript>1/2</Subscript>TiO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–Sr<Subscript>3</Subscript>CuNb<Subscript>2</Subscript>O<Subscript>9</Subscript> lead-free piezoelectric ceramics

The structure, microstructure, field-induced strain, ferroelectric, piezoelectric and dielectric properties of (1 ? x) (Bi_0.5Na_0.5)_0.935Ba_0.065TiO₃–xSr₃CuNb₂O₉ (BNT-BT6.5–xSCN, with x = 0, 0.003, 0.006, 0.009) ceramics were investigated. X-ray diffraction patterns show that all samples are pure perovskite structure and Sr₃CuNb₂O₉ (SCN) effectively diffused into the 0.935Bi_0.5Na_0.5TiO₃–0.065BaTiO₃ (BNT–BT6.5) solid solution which also reflected in the Raman spectra and the energy disperse spectroscopy (EDS) analysis. With the increases of SCN content, the coercive field (E _c  = 18.41 kV/cm) decreases greatly, whereas the remnant polarization (P _r  = 29.11 μC/cm²) increases a little at x = 0.003 which is showed in the polarization hysteresis (P–E) loops, the result indicate that the ferroelectric order would be disrupted. Around critical composition (x = 0.003) at a driving field of 60 kV/cm, a large unipolar strain of 0.29 % with a normalized strain (d ₃₃ ^*  = 483 pm/V) is obtained at room temperature. The results indicate that BNT-BT6.5-xSCN ceramics with excellent properties are promising to replace lead-based piezoelectric ceramics and can be used in practical applications.     

Phase formation and dielectric properties of ceramics in the BiFeO<Subscript>3</Subscript>–BaTiO<Subscript>3</Subscript>–Bi(Mg<Subscript>0.5</Subscript>Ti<Subscript>0.5</Subscript>)O<Subscript>3</Subscript> system

We have studied the effect of Bi(Mg_0.5Ti_0.5)O₃ additions on the phase formation, structural parameters, microstructure, and dielectric properties of solid solutions in the region of a morphotropic phase boundary in the BiFeO₃–BaTiO₃ system. Single-phase samples with the perovskite structure have been obtained and the addition of Bi(Mg_0.5Ti_0.5)O₃ has been shown to raise the Curie temperature of the ceramics and improve their dielectric properties.     

Preparation and properties of Bi<Subscript>6</Subscript>Ti<Subscript>5</Subscript>WO<Subscript>22</Subscript>: a new phase in the Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–TiO<Subscript>2</Subscript>–WO<Subscript>3</Subscript> system

In a recent report, the evaluation of the phase relations in the Bi₂O₃–TiO₂–WO₃ ternary system has shown the existence of a new phase with nominal composition close to Bi₆Ti₅WO₂₂. In the present contribution we attempt to prepare this single phase by using a solid state route. Although XRD analyses also show traces of two minority Aurivillius-type phases in the synthesized materials, the crystal structure of the Bi₆Ti₅WO₂₂ phase has been determined by Rietveld analyses revealing a complex structure similar to that of Bi₃(AlSb₂)O₁₁ and PbHoAl₃O₈ related compounds. The electrical response of this new phase was characterized as well. Three peaks are observed in its dielectric response: two of them positioned around 0 °C and can be assigned to this Bi₆Ti₅WO₂₂ structure. The third one rises up to 665 °C and confirms the presence of the Aurivillius-type phases.     

Synthesis and Structure of Mixed Cromate–Nitrate Complexes of Hexavalent Actinides, [(CH<Subscript>3</Subscript>)<Subscript>4</Subscript>N][(AnO<Subscript>2</Subscript>)(CrO<Subscript>4</Subscript>)(NO<Subscript>3</Subscript>)] (An = U,Np, Pu)

Mixed-anion compounds of the general composition [(CH₃)₄N][(AnO₂)(CrO₄)(NO₃)], where An = U, Np, and Pu, were synthesized and structurally characterized. The structural motif of these compounds is based on anionic ribbons of the composition [AnO₂(NO₃)(CrO₄)]_n^n–, consisting of seven-vertex An polyhedra linked via oppositely oriented CrO₄ tetrahedra and NO₃ groups acting in the An polyhedra as terminal bidentate ligands. Every four anionic ribbons form channels oriented along b-axis. Tetramethylammonium cations linked with the O atoms of the ribbons by hydrogen bonds are located in these channels. Actinide contraction is observed in the series U–Np–Pu. It is manifested in a regular decrease in the interatomic distances in the An polyhedra, in parameters b and c, and in the unit cell volume.     

Study on the mechanism of NH<Subscript>3</Subscript>-selective catalytic reduction over CuCe<Subscript>x</Subscript>Zr<Subscript>1–x</Subscript>/TiO<Subscript>2</Subscript>

Copper-cerium-zirconium catalysts loaded on TiO₂ prepared by a wet impregnation method were investigated for NH₃-selective catalytic reduction (SCR) of NO_x. The reaction mechanism was proposed on the basis of results from in situ diffuse reflectance infrared transform spectroscopy (DRIFT). When NH3 is introduced, ammonia bonded to Lewis acid sites is more stable over CuCe_0.25Zr_0.75/TiO₂ at high temperature, while Brønsted acid sites are more important than Lewis acid sites at low temperature. For the NH₃+NO+O₂ co-adsorption, NH3 species occupy most of activity sites on CuCe_0.25Zr_0.75/TiO₂ catalyst, and mainly exist in the forms of NH₄ ⁺ (at low temperature) and NH₃ coordinated (at high temperature), playing a crucial role in the NH₃-SCR process. Two different reaction routes, the L-H mechanism at low temperature (< 200°C) and the E-R mechanism at high temperature (> 200°C), are presented for the SCR reaction over CuCe_0.25Zr_0.75/TiO₂ catalyst.