TiO3 Solid Solution Research Articles

Effects of Co doping on structural, magnetic, and electrical properties of 0.6BiFeO3-0.4(Bi0.5K0.5)TiO3 solid solution

The effects of Co doping on structural, dielectric, and magnetic properties of multiferroic 0.6BiFe1-xCoxO3-0.4(Bi0.5K0.5)TiO3 (0 ≤ x ≤ 0.2) ceramics have been investigated. The samples undergo a structural transition from pseudocubic to rhombohedral phase at x = 0.1. The maximum remnant polarization of 57.8 μC/cm2 and remnant magnetization of 0.107 emu/g are observed in the x = 0.15 sample. The ferromagnetism is proposed to originate from the suppression of spiral spin structure with the canting of the antiferromagnetically ordered spins caused by the substitution of Co for Fe ions. Moreover, the magnetodielectric effect can be observed in the x = 0.15 sample.

Perovskite structure and low frequency relaxor- like- dielectric response of (Sr,Ce)TiO3 solid solution

Phase composition, structure stability, cations valance state, and relaxor-like-dielectric behavior of Sr(1–3/2x)CexTiO3 (SCT, x = 0.3, 0.4) solid solution were investigated systematically. The Sr(1–3/2x)CexTiO3 samples appear to be single phase within the detection limits of the technique, whereas the solid solution exhibits the higher angle doublet and triplet peak splitting associated with (200) and (321). X-ray photoelectron spectroscopy (XPS) analysis showed that the Ce substitution induces change in the cations valance state upon oxygen vacancies formation. The system exhibits features of low-frequency dependent relaxor-like-dielectric behavior rather than sharp frequency-independent anomalies. Besides this, two kind of relaxations were detected in the temperature range ≥ 350°C. According to the electric modulus and ac conductivity analysis, the relaxor-like-dielectric behavior results from the long-range conduction associated with ionized vacancies and mixed state of Ti3+/4+ and Ce3+/4+ cations.

Phase–composition and temperature dependence of electrocaloric effect in lead–free Bi0.5Na0.5TiO3–BaTiO3–(Sr0.7Bi0.2□0.1)TiO3 ceramics

The (0.94–x)Bi0.5Na0.5TiO3–0.06BaTiO3–x(Sr0.7Bi0.2□0.1)TiO3 (BNT–BT–xSBT, 0≤x≤0.24) solid solution ceramics were synthesized via a conventional solid–state reaction method and the correlation of phase structure, piezoelectric, ferroelectric properties and electrocaloric effect (ECE) was investigated in detail. The ECE in lead–free BNT–BT–xSBT ceramics was measured directly using a home–made adiabatic calorimeter with maximum adiabatic temperature change ΔT=0.4K with x=0.08 under the electric field E=6kV/mm at room temperature. The position of maximum ECE was found in the vicinity of nonergodic and ergodic phase boundary, where the maximum change in entropy occurs as a result of the field–induced phase transformation between the ergodic and long–range ferroelectric phase. Besides, the mechanism for the shift of ECE peak is discussed in detail. Finally, the temperature dependence of ECE for BNT–BT–xSBT (x=0, 0.04 and 0.08) was also investigated. This work may present a guideline for designing BNT–based ferroelectric relaxor ceramics for EC cooling technologies.

Structural, Optical, and Magnetic Properties of Lead-Free Ferroelectric Bi0.5K0.5TiO3 Solid Solution with BiFeO3 Materials

A solid solution of Bi0.5K0.5TiO3-BiFeO3 was fabricated by a sol–gel technique. The pure Bi0.5K0.5TO3 samples exhibited weak room-temperature ferromagnetism. The room-temperature ferromagnetism was observed in BiFeO3 solid solution in Bi0.5K0.5TiO3. The optical band gap of Bi0.5K0.5TiO3 was reduced from 3.22 eV to 1.39 eV with the increase in the amount of BiFeO3 solid solution. The room-temperature ferromagnetism and band gap reduction were attributed to the diffusion of BiFeO3 into Bi0.5K0.5TiO3 to form a solid solution. Our work provided a simple method of realizing room-temperature ferromagnetism in lead-free ferroelectric materials.

Study of nanomechanical properties of (1-y)BST-yMgO thin films

In the present study thin films of MgO – modified Ba0.6Sr0.4TiO3 (BST60/40) solid solution were prepared by the sol-gel-type chemical solution deposition method on stainless steel substrates. A multilayer spin-coating approach was utilized for the Ba0.6Sr0.4TiO3-MgO thin film deposition with subsequent thermal annealing at T=650-750°C. Dried BST60/40-MgO gel powders were studied with thermogravimetric and differential thermal analysis to determine their thermochemical properties. X-ray diffraction analysis was utilized for thin film characterization in terms of its phase composition and crystal structure. The influence of y=1, 3 and 5 mol.% MgO doping on nanomechanical properties of BST60/40 thin films was studied with nanoindentation. It was found that BST6040 thin films adopted the tetragonal P4mm (99) structure. The volume of the BST60/40 elementary cell, the average hardness as well as the mean value of the Young modulus decreased with an increase in amount of MgO.

Catalytic reduction of SO2 by CO over CeO2–TiO2 mixed oxides

The structure and catalytic desulfurization characteristics of CeO2–TiO2 mixed oxides were investigated by means of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and catalytic activity tests. According to the results, a CeO2–TiO2 solid solution is formed when the mole ratio of cerium to titanium n(Ce):n(Ti) is 5:5 or greater, and the most suitable n(Ce):n(Ti) is determined as 7:3, over which the conversion rate of SO2 and the yield of sulfur at 500 °C reach 93% and 99%, respectively. According to the activity testing curve, Ce0.7Ti0.3O2 (n(Ce):n(Ti)=7:3) without any pretreatment can be gradually activated by reagent gas after about 10 min, and reaches a steady activation status 60 min later. The XPS results of Ce0.7Ti0.3O2 after different time of SO2+CO reaction show that CeO2 is the active component that offers the redox couple Ce4+/Ce3+ and the labile oxygen vacancies, and TiO2 only functions as a catalyst structure stabilizer during the catalytic reaction process. After 48 h of catalytic reaction at 500 °C, Ce0.7Ti0.3O2 still maintains a stable structure without being vulcanized, demonstrating its good anti-sulfur poisoning performance.

Microwave dielectric properties of Na0.5Sm0.5TiO3-based ceramics

The effect of calcining and sintering conditions on the microwave dielectric properties of Na0.5Sm0.5TiO3 (NST) solid solutions were investigated. The results showed that, after being calcined at 1100 °C for 2 h, the proposed NST system sintered at 1350 °C for 4 h exhibited a good microwave dielectric properties. Additionally, the phase assemblages, crystal structures, microstructures and microwave dielectric properties of the Na0.5Sm0.5[Ti1−x(Al0.5Ta0.5)x]O3 (NSTATx, 0.1 ≤ x ≤ 0.3) and (1 − x)Na0.5Sm0.5TiO3–xSm(Mg0.5Ti0.5)O3 (NST–SMTx, 0.1 ≤ x ≤ 0.4) ceramics were also investigated in this work. The X-ray diffractometer results revealed that a tilted orthorhombic perovskite structure in space group Pnma was refined in the NSTATx ceramics, while the Ti7O13 phase, Sm2Ti2O7 phase, and some unknown phase were detected gradually in NST–SMTx ceramics with increasing x value. Moreover, for the NSTATx solid solutions, a decreasing permittivity (er) and a significant drop in quality factor (Q × f) were strongly correlated with ionic polarizability and grain sizes, respectively. On the other hand, the er and Q × f values of the NST–SMTx ceramics were strongly depended on the composition and phase assemblages. Furthermore, the temperature coefficient of the resonant frequency (τf) of the present ceramic systems could be adjusted by the changed tilting of oxygen octahedra. An optimized microwave dielectric properties with er ~ 59.4, Q × f ~ 22,200 GHz (at 4.06 GHz) and τf ~ 6.1 ppm/°C can be obtained in the NST–SMTx (x = 0.3) specimen sintered at 1450 °C for 4 h.

Influence of (Bi<sub>0.5</sub>M<sub>0.5</sub>)TiO<sub>3</sub> (M=Li, Na, K, Rb) Addition on the Curie Temperature and PTC Effect of BaTiO<sub>3</sub>-Based Ceramics

In order to investigate the influence of (Bi0.5M0.5)TiO3 (M=Li, Na, K, Rb) addition on the Curie temperature (Tc) and positive temperature coefficient (PTC) effect of BaTiO3-based ceramics, BaTiO3-(Bi0.5M0.5)TiO3 (M=Li, Na, K, Rb) solid solutions were prepared by a conventional solid sintering reaction using high-purity reagents. It was found that the Tc of the samples would vary with (Bi0.5M0.5)TiO3 of different alkali ions, in which BT-BKT ceramics had the highest value (about 148 °C). Moreover, the incorporation of alkali ions would influence the PTC effect of the sample, which can be defined by the resistivity jump with the ratio of maximum to minimum resistivity (ρmax/ρmin). Under the present conditions, the ρmax/ρmin of BT-BRT and BT-BLT ceramics were almost equal and higher than those of BT-BNT and BT-BKT ceramics.

Phase transitions in Na0.5Bi0.5TiO3-(Sr0.7Bi0.2)TiO3-PbTiO3 solid solutions

ABSTRACTIncreasing of Sr0.7Bi0.2TiO3 concentration in Na0.5Bi0.5TiO3-Sr0.7Bi0.2TiO3 solid solutions causes increasing of Bi/Na relation and vacancies in the A-site of perovskite structure. In temperature dependence of dielectric permittivity, such a change of composition is reflected by transforming of the frequency-dependent shoulder into a maximum characteristic for relaxor ferroelectrics and diminishing of the frequency-independent maximum characteristic for Na0.5Bi0.5TiO3. Here changes in behavior of dielectric permittivity and polarization are studied if PbTiO3 is added in a certain concentration range of Na0.5Bi0.5TiO3-Sr0.7Bi0.2TiO3 solid solutions. Changes of the characteristic temperatures as a function of PbTiO3 concentration are determined. Behavior of the electrocaloric effect is compared with the results obtained for Na0.5Bi0.5TiO3-SrTiO3-PbTiO3.

Semi-oxalate synthesis of (1−x)BaTiO3−xM0.5Bi0.5TiO3 (M = Li, Na, K) PTCR materials

(1−x)BaTiO3–xM0.5Bi0.5TiO3 (M = Li, Na, K) solid solutions were prepared using BaTiO3 pre-synthesized by oxalate method. The stability limits of (1−x)BaTiO3–xLi0.5Bi0.5TiO3 solid solutions have been established. It was shown that increase in M0.5Bi0.5TiO3 concentration results in reduction of ceramic grain size in the (1−x)BaTiO3−xM0.5Bi0.5TiO3 (M = Li, Na, K) system. It was found that the positive temperature coefficient of resistance (PTCR) effect in lead-free materials is due to the presence of a semiconductor core, which is formed by sintering under reducing atmosphere, and dielectric grain boundaries, formed on additional oxidation in air. The use of barium titanate, pre-synthesized by oxalate method, in the synthesis of solid solutions reduced the sintering temperature of ceramics compared with solid state reaction technique. By comparing the electrical properties of the synthesized lead-containing and lead-free materials, it has been shown that lead-free materials exhibit better electrical properties for practical use compared with lead-containing materials.

Synthesis, X-ray structure analysis, and Raman spectroscopy of R2TiO5-based (R = Sc, Y) solid solutions

Order–disorder transitions in xR2O3 · (1 − x)TiO2 (R = Sc, 0.4 ≤ x ≤ 0.5; R = Y, 0.5 ≤ x ≤ 0.6) solid solutions with highly imperfect fluorite-derived structures have been studied using monochromatic synchrotron X-ray diffraction and Raman spectroscopy. The results demonstrate that the synthesis process leads to the formation of a fluorite-like (Fm3m) disordered phase and a nanoscale (~10–100 nm) pyrochlore-like (Fd3m) ordered phase of the same composition, coherent with the disordered phase. We have determined their lattice parameters. The Raman spectra of Sc2TiO5 (Y2TiO5) contain broad lines in low- and high-frequency regions: at 190, 350, and 775 (134, 188, 365, 404, and 727) cm−1. These lines are characteristic of a pyrochlore-like phase with a varying degree of order and a disordered fluorite-like phase, respectively. The pyrochlore-like phase Y2Ti2O7 has two strong Raman peaks in the low-frequency region: at 312 and 527 cm−1. The formation of nanodomains with different degrees of order is caused by the internal stress that arises from the high density of structural defects in the unit cells of the solid solutions.

Structural, dielectric and electrocaloric properties in lead-free Zr-doped Ba0.8Ca0.2TiO3 solid solution

Abstract We investigate in the present work the additional data points ( x =0.02, 0.06 and 0.08) to the previous reported paper (Asbani et al., 2015) [21] that sufficiently enrich to understand the EC properties and underlying phase diagram of the lead-free Ba 0.8 Ca 0.2 Ti (1− x ) Zr x O 3 ( x BCTZ) system. X-ray diffraction analysis performed at room temperature, confirms a continuous tetragonal solid solution with P 4 mm (No. 99) space group that evolved to pseudo-cubic symmetry for the high Zr-content compounds. Ferroelectric and paraelectric behaviors were highlighted using P–E hysteresis data versus temperature. Phase transition was confirmed by dielectric permittivity measurements versus temperature showing a decrease of the Curie temperature when Zr-content increases. From P–E hysteresis recording the electrocaloric temperature change (Δ T ) was calculated that ranged in between 0.12 and 0.27 K and the electrocaloric responsivity ( ξ ) in 0.15 to 0.34×10 −6 K·m/V under 7.95 kV/cm applied electric field. The zero-field entropy is compared to electrocaloric isothermal entropy to estimate the extent the EC is being under-driven.

Microstructure and optical characterizations of mechanosynthesized nanocrystalline semiconducting ZrTiO4 compound

A ZrO2–TiO2 solid solution is obtained by high energy ball milling of equimolar mixture of monoclinic (m) ZrO2 and anatase (a) TiO2. Nanocrystalline orthorhombic ZrTiO4 compound is initiated from the nucleation of TiO2–ZrO2 solid solution with isostructural s-TiO2 (srilankite) base after 30min of milling. After 12h of milling, 95mol% non-stoichiometric ZrTiO4 phase is formed. Post-annealing of 12h ball-milled powder mixture at 1073K for 1h in open air results in complete formation of stoichiometric ZrTiO4 compound. Microstructures of all powder mixtures milled for different durations have been characterized by Rietveld's structure and microstructure refinement method using X-ray powder diffraction data. HRTEM images of 12h milled and annealed samples provide direct evidence of the results obtained from the Rietveld analysis. Optical bandgaps of ball milled and annealed ZrTiO4 compounds lie within the semiconducting region (~2.0eV) and increases with increase in milling time.

Lanthanide doped BaTiO3[sbnd]SrTiO3 solid-solution phosphors: Structure, optical spectroscopy and upconverted temperature sensing behavior

Lanthanide doped Ba1-xSrxTiO3 (x = 0–1) solid-solution phosphors were successfully prepared by a conventional solid-state reaction. Using Eu3+ dopants as the structural probe, the variation of 5D0 → 7F2/5D0 → 7F1 emission intensity ratio with increase of Eu3+ content and the excitation-wavelength-dependent luminescence in the Ba1-xSrxTiO3 sample were demonstrated to be originated from the different emission behaviors of Eu3+ in Ba2+/Sr2+ site and Ti4+ site. Furthermore, upconversion luminescence for the Yb3+/Er3+ co-doped Ba1-xSrxTiO3 samples were investigated, and it was found that the emission intensity of Yb3+/Er3+: Ba0.5Sr0.5TiO3 phosphor was about 5 and 2 times as high as those of Yb3+/Er3+: BaTiO3 and Yb3+/Er3+: SrTiO3 ones. Using the investigated Yb3+/Er3+: Ba0.5Sr0.5TiO3 solid-solution as the optical thermometric medium, the temperature sensitivity was determined to be 0.76% K−1 at the temperature of 610 K based on the temperature-dependent fluorescence intensity ratio of the thermally coupled 2H11/2 and 4S3/2 emitting-states of Er3+.

Isomerization of glucose at hydrothermal condition with TiO2, ZrO2, CaO-doped ZrO2 or TiO2-doped ZrO2

Catalytic activity of TiO2, ZrO2 and ZrO2 solid solutions (with CaO or TiO2) for the isomerization of glucose into fructose under hydrothermal conditions (120–180°C for 5–15min reaction time) was evaluated by experimental kinetic studies and surface acidity–basicity measurements. Kinetic studies were conducted with batch reactors heated by microwave. Under hydrothermal conditions regardless of the temperature, fructose yield was always below 10% and fructose selectivity was rapidly decreased with increasing glucose conversion. By adding 10mM NaOH, fructose yield reached 20% at 160°C for 5min. In the presence of TiO2, fructose yield and selectivity were similar (160°C, 47% of glucose conversion and 14% fructose yield). ZrO2 showed higher catalytic activity (160°C, 63% glucose conversion and 21% fructose yield) compared with TiO2. The catalytic activity of TiO2 doped ZrO2 was between TiO2 and ZrO2. To increase the basicity of ZrO2, CaO was doped into the ZrO2 matrix. For experiments with the 24wt% CaO doped ZrO2, fructose selectivity was higher than 70% even at 30% glucose conversion at 160°C for 15min. For systematical understanding catalytic activity of the metal oxides used, acidity and basicity of the catalysts were measured by temperature programmed desorption (TPD) using either CO2 or NH3. It was found that basicity on the surface increased with increasing the amount of CaO in the ZrO2 solid solution while acidity increased with amounts of TiO2. For a simple network model of glucose reactions, rate constants were fitted to the data assuming a simple network model and they were completed with the acid-base properties of TiO2, ZrO2 and CaO doped and TiO2 doped ZrO2. As a result, the reactivity was found to be correlated with the ratio of the base to acid sites on the surface and fructose formation was linearly proportional to the base/acid mole ratio on the surface of the catalysts.

Effect of annealing temperature on the multiferroic properties of 0.7BiFeO3–0.3Bi0.5Na0.5TiO3 solid solution prepared by sol–gel method

Room-temperature multiferroic 0.7BiFeO3–0.3Bi0.5Na0.5TiO3 solid solution ceramics have been prepared by the sol–gel method. We have discussed the annealing temperature dependence of the multiferroic properties. The samples are annealed at 1023, 1123, 1223 and 1323K for 3h, respectively. X-ray diffraction patterns identify that all samples are pure. Scanning electron micrographs present the increasing grain size with higher annealing temperature. Magnetic, ferroelectric and dielectric properties are enhanced obviously with the increase in annealing temperature. The coexistence of ferroelectric and ferromagnetic properties is also proved at room temperature. In addition, it reveals that the optimal annealing temperature accompanied with favorable multiferroic properties of 0.7BiFeO3–0.3Bi0.5Na0.5TiO3 solid solution ceramics is near 1223K.

Comparison of concentrations of BaZr x Ti(1–x)O3 solid solutions synthesized from various powder mixtures

The dependence of concentration of synthesized BaZrxTi(1–x)O3 solid solutions on the type of original mixture of BaTiO3 + ZrO2 or BaCO3 + TiO2 + ZrO2 powders was established. The influence of particle sizes of ZrO2 (microor nanopowders) on the concentration was revealed.

The Nanocrystalline SnO2–TiO2 System‒Part II: Surface Energies and Thermodynamic Stability

The thermodynamic stability of nanocrystalline SnO2–TiO2 solid solutions was studied experimentally. Microcalorimetry of water adsorption revealed a systematic decrease in the surface energy with increasing Ti4+ content in the SnO2‐rich compositions, consistent with previous reports of Ti4+ segregation on the surface. The surface energy change was accompanied by an increase in the magnitude of the heat of water adsorption, also indicating a modification of the SnO2 surface by Ti4+. Supporting the water adsorption data, calculations using high‐temperature oxide melt solution calorimetry data also suggest a decrease in the interface energies. A thermodynamic analysis showed that the observed surface energy decrease is responsible for an increase in the stability of solid solutions in the nanophase regime. Although a miscibility gap is expected in this system from bulk phase diagrams, the surface energy contribution modifies the bulk trend and promotes extensive solid solutions when the surface area is above a critical value dependent on the surface energy and the bulk enthalpy of mixing.

Complex Impedance Analyses of Ba<sub>1-</sub><i><sub>x</sub></i>Li<sub>0.5</sub><i><sub>x</sub></i>Bi<sub>0.5</sub><i><sub>x</sub></i>TiO<sub>3</sub> Solid Solution PTCR Ceramics

Conditions for the formation of (1-x)BaTiO3–xLi0.5Bi0.5TiO3 (0 ≤ x ≤0.6) solid solutions with positive temperature coefficient of resistance (PTCR) effect were studied. Solid solutions were prepared by solid state reaction technique. Samples were sintered under reducing atmosphere N2/H2 in the temperature range 1200–1450 °C with subsequent oxidation in air. The phase composition was investigated by X-ray powder diffraction method. It was found that samples of (1-x)BaTiO3–xLi0.5Bi0.5TiO3 (0 ≤ x ≤0.6) solid solutions at room temperature exhibit perovskite structure. Unit cell parameters of unstable at the room temperature compound Li0.5Bi0.5TiO3 were determined by extrapolation of concentration dependence of the unit cell parameters in the (1-x)BaTiO3–xLi0.5Bi0.5TiO3 system. It was shown that minimum value of resistivity ρmin rises with increase in x value. Complex impedance method shown that ceramic grains of (1-x)BaTiO3–xLi0.5Bi0.5TiO3 materials consist of three areas with different electrical properties. Boundary and outerlayer region of grains make the main contribution to the PTCR effect in lithium-containing solid solutions. It was shown that magnitude of the potential barrier's decreases with increasing x.

Effect of Li2CO3 addition on the structural, optical, ferroelectric, and electric-field-induced strain of lead-free BNKT-based ceramics

In this work, we reported the effect of Li2CO3 addition on the structural, optical, ferroelectric properties and electric-field-induced strain of Bi0.5(Na,K)0.5TiO3 (BNKT) solid solution with CaZrO3 ceramics. Both rhombohedral and tetragonal structures were distorted after adding Lithium (Li). The band gap values decreased from 2.91 to 2.69eV for 5mol% Li-addition. The maximum polarization and remanent polarization decreased from 49.66μC/cm2 to 27.11μC/cm2 and from 22.93μC/cm2 to 5.35μC/cm2 for un-doped and 5mol% Li- addition BNKT ceramics, respectively. The maximum Smax/Emax value was 567pm/V at 2mol% Li2CO3 access. We expected this work will help to understand the role of A-site dopant in lead-free ferroelectric BNKT materials.