Narrow Results

A well-aligned single-crystalline barium titanate (BaTiO₃) nanostructured layer was prepared by the growth and conversion of vertically aligned TiO₂ nanorods. This was achieved through a two-step hydrothermal method on fluorine-doped tin oxide (FTO)-coated glass substrates via the dissolution-nucleation-recrystallization mechanism. The morphology, crystal structure and optical properties were investigated using field-emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD), Raman spectroscopy, photoluminescence (PL) and Z-scan techniques. The X-ray and selected area diffraction patterns (SAED) confirmed the formation of the aligned single-crystalline tetragonal BaTiO₃ layer. The room temperature Raman spectrum showed the tetragonal TiO₂-related vibrational modes in BaTiO₃. The PL spectra indicated the coalescence of band edge emissions of BaTiO₃ and TiO₂ in the blue and visible regions of the investigated spectra. The Z-scan experiments performed using the CW Nd:YAG laser revealed a positive nonlinear refractive index on the order of 10${}^{-7}$ cm²W${}^{-1}$, indicating the self-focusing type of cation in the BaTiO₃ sample. The nonlinear absorption coefficient of the BaTiO₃ nanostructures in the order of 10${}^{-7}$ cm W${}^{-1}$ was also calculated. As expected, the BaTiO₃ nanostructure synthesized in this study is a good candidate for use in nonlinear optics.

0.8BaTiO₃–0.2Bi_0.5K_0.5TiO₃ (BT–BKT20) lead-free ceramics were prepared by conventional solid state reaction method followed by high energy ball milling. The formation of a single phase tetragonal structure in the material was confirmed by X-ray diffraction. Frequency and temperature-dependent dielectric studies show relaxor behavior in the BT–BKT20 which was found to obey modified Curie–Weiss law with degree of diffuseness 1.573. Complex impedance and electric modulus spectroscopy studies reveal temperature-dependent relaxation process in the material. The Cole–Cole plots were measured at high temperatures at which grain effect was observed. Impedance and electric modulus spectroscopy studies show non-Debye kind of conductivity relaxation process in the present material. Activation energies were calculated from impedance and electric modulus spectroscopy and the values of activation energy indicated that the conduction is ionic in nature. AC and DC conductivity have been measured and studied at different temperatures.

A modified barium vacancy formation mechanism in donor-doped barium titanate (BaTiO₃) ceramics is proposed. Assuming a uniform distribution of barium vacancies at sintering temperature and only oxygen partial pressure and sintering temperature related concentration of unionized barium vacancies, the electrical characteristics have been calculated by solving a differential equation about electron level. The room-temperature resistivity and positive temperature coefficient of resistivity (PTCR) behaviors of donor-doped BaTiO₃ semiconducting ceramics have been quantitatively computed. The results pointed out that the room-temperature resistivity changes as a U-type curve with an increase of donor concentration. Moreover, the PTCR effect of BaTiO₃ semiconductive ceramics was calculated quantitatively under different conditions. Theoretical and experimental results for BaTiO₃ semiconductive ceramics are compared and discussed.

The influence of Nb₂O₅-doped concentration on the positive temperature coefficient of resistance (PTCR) effect, electrical properties and microdefects of (Ba${}_{0.95}$Sr${}_{0.05}$)(TiNb${}_x$)O₃ (BSTN) ceramics were investigated. Firing was conducted at 1350${}^{\circ }$C for 2 h in air. The donor-doped content affected the electrical properties, PTCR effect and formation of the microdefect type of the BSTN samples. The room temperature resistivity of the BSTN specimens first decreased and then increased with increasing donor-doped content in the range of 0.2 mol.% Nb${}^{5+}$ to 0.5 mol.% Nb${}^{5+}$. Moreover, the information on microdefects in BSTN ceramics was demonstrated by coincidence Doppler broadening spectrum. The influence of the defects on the PTCR characteristics of the ceramics was also revealed.

This study investigates the influence of dopant content and firing conditions on electrical properties and positive temperature coefficient of resistance (PTCR) effect of Ba${}_{1.005}$(Ti${}_{1-x}$Nb${}_x)$O₃ (BTN) ceramics sintered at different temperatures from 1070${}^{\circ }$C to 1220${}^{\circ }$C for 2 h in a reducing atmosphere and reoxidized within the temperature range of 600–750${}^{\circ }$C for 0.5–8 h. The results indicate that the room-temperature (RT) resistance of the laminated BTN specimens initially decreased and then increased as a function of the dopant concentration. Moreover, the resistance jump exhibited a contrasting tendency. Furthermore, the RT resistance of the BTN samples rapidly decreased at first and then gradually decreased with increasing sintering temperature. Meanwhile, the resistance jump of the samples increased first and then decreased. In addition, the influence of reoxidation times on the PTCR characteristics of ceramics was investigated.

Using a supercell model and a hybrid B3PW exchange-correlation functional, we have performed first principles calculations for the F-center in the BaTiO₃ bulk and on the BaO-terminated (001) surface. We find that two Ti atoms nearest to the bulk F-center are repulsed, while nearest eight oxygen and four barium atoms relax toward the oxygen vacancy (by 1.06, 0.71 and 0.08% of the lattice constant $a_0$, respectively). The magnitudes of atomic displacements around the F-center located on the BaO-terminated (001) surface in most cases (except for Ti) are larger than those around the bulk F-center (0.1, 1.4 and 1.0% of $a_0$, respectively). Our calculated BaTiO₃ bulk $\mathrm{\Gamma }$–$\mathrm{\Gamma }$ bandgap of 3.55 eV is in an acceptable agreement with the respective experimental bandgap value of 3.2 eV. The pristine BaO-terminated (001) surface $\mathrm{\Gamma }$–$\mathrm{\Gamma }$ bandgap (3.49 eV) is reduced with respect to the bulk bandgap value. The bulk and BaO-terminated (001) surface F-center bands in BaTiO₃ matrix are located only at 0.23 eV and 0.07 eV under the conduction band (CB) bottom, indicating that the F-center is a shallow donor. The F-center in the BaTiO₃ bulk contains charge of 1.103$e$, whereas slightly less charge, only 1.052$e$, are localized inside the F-center on the BaO-terminated (001) surface. Our calculations demonstrate considerable increase of the chemical bond covalency between the BaTiO₃ bulk F-center and its two nearest Ti atoms equal to 0.320$e$, and even larger increase for BaO-terminated (001) surface F-center and its nearest Ti atom 0.480$e$, in comparison to the relevant Ti–O chemical bond covalency in the perfect BaTiO₃ bulk 0.100$e$. The difference between F-center formation energy in BaTiO₃ bulk (10.3 eV) and on the BaO-terminated (001) surface (10.2 eV) trigger the segregation of the F-center from the bulk toward the BaO-terminated (001) surface.

Polyvinyl chloride (PVC) is widely used as insulator in electrical engineering especially as cable insulation sheaths. In order to improve the dielectric properties, polymers are mixed with ceramics. In this paper, PVC composites with different weight percentages 2 wt.%, 5 wt.%, 8 wt.% and 10 wt.% were prepared and investigated. Loss index (${𝜀}^{″}$) and dielectric constant (${𝜀}^{\prime }$) have been measured using an impedance analyzer RLC. Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) have been used as characterization techniques. The incorporation of BaTiO₃ does not modify the crystallinity and the morphology of the PVC but reduces the space charges, therefore the dielectric losses. The frequency response analysis has been followed in the frequency ranges (20–140 Hz and 115–1 MHz). Relaxation frequencies have been evaluated in each frequency range. Experimental measurements have been validated using Cole–Cole’s model. Experimental results show well that BaTiO₃ as a filler improves the dielectric properties of PVC.

Crystal structure of ${\mathrm{\text{BaTiO}}}_3$ compound was studied using Atomistix Tool Kit software program at high pressure. It is defined that in this combination, tetragonal–cubic phase transition occurs under high pressure $P\approx 2$ GPa. The character of this phase transition is explained in respect of baric dependence of spontaneous strain. Birch–Murnaghan equation is solved, compression ratio is determined. Results gained by theoretical calculations are compared with experimental values.

This study investigates the influence of sintering conditions on electrical properties and positive temperature coefficient of resistance (PTCR) of ${\mathrm{\text{Ba}}}_{1.005}({\mathrm{\text{Ti}}}_{1-x}{\mathrm{\text{Nb}}}_x){\mathrm{\text{O}}}_3$ (BTNO) ceramics, fired at $1190^{\circ }$C for different times from 1 to 6 h in a reducing atmosphere and reoxidised within the temperature range of $600$–$900^{\circ }$C for 1 h. The results showed that the room-temperature (RT) resistance and the resistance jump of the multilayer BTNO ceramics decreased with an increase in the firing time. Furthermore, the RT resistance of the BTNO samples gradually increased at first and then rapidly increased with increasing reoxidation temperature. In addition, the influence of sintering times on the microstructure of ceramics was also investigated.

In this paper, we investigated the influence of cooling rates on electrical properties and positive temperature coefficient of resistance (PTCR) effect of (Ba_1.22−xSm_x)TiO₃ + 0.007 mol SiO₂ (BTS) ceramics, which were fired at 1200^∘C for 30 min in a reducing atmosphere and then reoxidized at 700–800^∘C for 1 h. The results showed that the room-temperature (RT) resistivity and the resistance jump of the chip-type BTS ceramics increased with an increase in the cooling rate. Furthermore, the RT resistivity of the BTS specimens gradually decreased at first and then increased with increasing donor-doping concentration. In addition, the influence of cooling rates on the microstructure of ceramics was also investigated.

Cerium-doped 0.8BaTiO₃-0.2Bi${}_{0.5}$K${}_{0.5}$TiO₃ with composition 0.8Ba0.2(Bi${}_{0.5}$K${}_{0.5}$)Ti${}_{1-x}$Ce${}_x$O₃ where x = 0.01, 0.02, 0.03, 0.04, 0.05, 0.06 lead free ceramics were prepared by conventional solid state reaction method followed by high energy ball milling. X-ray diffraction studies confirm the tetragonal structure at room temperature for all the Ce-doped samples. Lattice parameters and density were increasing with increase of Ce doping. Frequency and temperature dependent dielectric studies were carried out and indicate that the dielectric constant and Curie temperature are decreasing with increasing of Ce doping. All the Ce-doped samples exhibiting diffused and dispersive phase transitions with degree of diffuseness ranging from 1.4 to 2 calculated from the modified Curie–Weiss law. Impedance studies confirms the temperature dependent non-Debye kind of relaxation process in the material. From the Cole–Cole plots measured at high temperatures, reveals that the grain effect in the all Ce-doped samples. Impedance analysis studies also support the X-ray diffraction and dielectric studies that occupation of Ce both at A-site and B-site for small values of Ce doping.

Lead-free $x($Na${}_{0.5}$Bi${}_{0.5})$TiO₃–$(1-x)$Ba${}_{0.7}$Sr${}_{0.3}$Sn${}_{0.02}$Ti${}_{0.98}$O₃ (NBT–BSST) ceramics are prepared by a wet solid-phase reaction method. The effect of NBT/BSST ratio on phase structure, microstructure and dielectric properties has been investigated in detail. The X-ray diffraction (XRD) analysis illustrates that the composites are composed of tetragonal perovskite. With increasing NBT content, the ceramic capacitors display stronger temperature stability in its dielectric behavior. A great enhance of dielectric properties and other electric parameters is obtained in this system by properly modulating the compositions. For example, the composite ceramics with 30% NBT content possess a large dielectric constant $({𝜀}_{\mathrm{\text{r}}})$ of 3200 and a low dielectric loss $(tan\delta )$ of 0.09. The temperature coefficient of capacitance of NBT–BSST varies from −50% to 20% while the NBT content is 30% at the whole range of measured temperature. The results show that NBT–BSST ceramics are a good candidate of lead-free dielectric materials.

In this work, we investigate the influences of Ba/Ti ratio and sintering conditions on the characteristics of positive temperature coefficient of resistance (PTCR) and electrical properties of Ba${}_m$(Ti${}_{1-x}$Nb${}_x$)O₃ (BTN) ceramics. The ceramics were fired at 1190${}^{\circ }$C for 0.5–6.0 h in a reducing atmosphere and then reoxidized at 600–650${}^{\circ }$C for 0–8 h. The Ba/Ti ratio $(m)$ affected the electrical properties and PTCR effect of the BTN specimens. The room-temperature (RT) resistance of the BTN samples initially decreased $(0.994<m<1.006)$ and then increased $(1.006<m<1.018)$ as the Ba/Ti ratio increased. Moreover, BTN ceramics exhibit a pronounced PTCR effect, with a resistance jump greater by 3.0 orders of magnitude and a low 0.1 $\mathrm{\Omega }$ RT resistance at a low reoxidation temperature of 600${}^{\circ }$C after sintering under a reducing atmosphere. Furthermore, the average sample grain size increased along with the Ba/Ti ratio. In addition, the influence of the sintering time and the reoxidation time on the electrical properties and the PTCR effect were also investigated.

$0.99{\mathrm{\text{BaTiO}}}_{3-x}{\mathrm{\text{Fe}}}_2{\mathrm{\text{O}}}_{3-y}{\mathrm{\text{Nb}}}_2{\mathrm{\text{O}}}_5$ ceramics ($x+y=1$ mol.%, $x$:$y$ = 1:3, 2:3, 3:2, 3:1) were successfully prepared using the traditional solid-phase sintering method. The effects of the proportion doping (Fe/Nb) components on various properties of BaTiO₃ ceramics were studied. The X-ray diffraction showed that all solid solutions have the single cubic phase at room temperature, and that dielectric permittivity exhibits a maximum, Curie’s temperature at the peak. The ceramics have obvious peak shift effect: Curie’s temperature shifts to low temperature as Fe/Nb ratio increases. The high Fe/Nb ratio BaTiO₃ ceramic showed also an enhancement of the broadening effect for dielectric constant curve with respect to temperature, and dielectric permittivity peak reflected phase transition from rhombohedral to tetragonal polar-nano regions. Dielectric and ferroelectric properties of Fe/Nb co-doped BaTiO₃ ceramics have obvious enhanced ferroelectric properties and have slender hysteresis loop beneficial for energy storage materials.

This research is based on the idea to design the interface structure around the grains and thin layers between two grains, as a possible solution for deep microelectronic parameters integrations. The experiments have been based on nano-BaTiO₃ powders with Y-based additive. The advanced idea is to create the new observed directions to network microelectronic characteristics in thin films coated around and between the grains on the way to get and compare with global results on the samples. Biomimetic similarities are artificial neural networks which could be original method and tools that we use to map input–output data and could be applied on ceramics microelectronic parameters. This mapping is developed in the manner like signals that are processed in real biological neural networks. These signals are processed by using artificial neurons, which have a simple function to process input signal, as well as adjustable parameter which represents sensitivity to inputs. The integrated network output presents practically the large number of inner neurons outputs sum. This original idea is to connect analysis results and neural networks. It is of the great importance to connect microcapacitances by neural network with the goal to compare the experimental results in the bulk samples measurements and microelectronics parameters. The result of these researches is the study of functional relation definition between consolidation parameters, voltage (U), consolidation sintering temperature and relative capacitance change, from the bulk sample surface down to the coating thin films around the grains.

The pressure-driven phase transformation in polycrystalline BaTi${}_{1-x}$Fe_xO₃ ($x=1$%), synthesized by a solid-state reaction method, was investigated using synchrotron X-ray diffraction and Raman spectroscopy. All measurements were performed at room temperature within a large pressure range up to 36.5 GPa. The results clearly demonstrate a phase transformation from the ferroelectric tetragonal structure of P4mm symmetry to the paraelectric cubic structure of Pm-3m symmetry in the studied sample at the pressure of about 18 GPa. This phase transformation pressure is much higher than those previously reported for BaTiO₃-based systems, indicating the stabilization of the ferroelectric phase by doping 1% Fe into BaTiO₃. Feature modes of the tetragonal phase still persist while some new modes appear in the Raman spectra at pressures above 18 GPa. This is probably due to accumulated stress and/or local microscopic disorders in the sample, which are associated with the displacement of the Ti atoms along unit-cell diagonals.

Barium titanate (BaTiO${}_3)$ nanoparticles having small tetragonality were prepared via sol–gel technique followed by post-calcinations at 800^∘C. The tetragonal phase was confirmed by XRD and TEM measurements. The obtained nanoparticles were quasi-spherical in shape with particle size lying between 30nm and 35nm, as obtained by TEM. The prepared sample was further characterized by TGA, DSC, FTIR, UV-Vis and PL spectroscopy. The low tetragonality of the obtained nanoparticles accounts for the absence of endothermic–exothermic peak in the DSC curve. The UV-Vis spectrum reveals band gap narrowing and the PL spectrum shows a broad band covering a large part of the visible spectra with the PL intensity maximum at 568nm. The dielectric and electrical properties were studied using LCR and Two probe method, and it shows a decrease in the permittivity as well as the tetragonal to cubic phase transition temperature.

High purity (Ba_1-xCa_x)(Ti_1-yZr_y)O₃((x,y)=(0.00,0.00)–(0.50,0.50)) were synthesized by a composite-hydroxide-mediated approach at 200°C using a sealed tube with a rolling system. The powders with an average size of 50 nm in diameter and narrow size distribution were produced. The highest electromechanical coupling factor k_r was 36.1% ((x,y) = (0.05,0.03)) and highest mechanical quality factor Q_m was 256 ((x,y) = (0.11,0.13)).

A three-phase composite film was produced by inserting multi-walled carbon nanotubes (MWCNTs) and BaTiO₃ nanoparticles into polyimide (PI). The combination of in-situ polymerization and water-based preparation involved in the experiment ensured fillers’ homogeneous dispersion in the matrix, which led to flexible shape of the composite films. The dielectric properties of composite films as a function of the frequency and the volume fraction of MWCNTs were studied. Such composite film displayed a high dielectric constant (314.07), low dielectric loss and excellent flexibility at 100Hz in the neighborhood of percolation threshold (9.02 vol%) owing to the special microcapacitor structure. The experimental results were highly consistent with the power law of percolation theory.

Perovskite ferroelectric BaTiO₃ material showed promising application in the photovoltaic field due to its positive polarization enhanced open voltage with ferroelectric modulation. Achieving perfect interfaces between the multi-layers based on BTO film was still unresolved. Therefore, we developed the bottom buffer layers SrTiO₃/Ti${}_{2.5}$O₃ films deposited on GaAs for reducing the lattice mismatch between the epitaxial oxide (BTO) GaAs via PLD system. The out-of-plane epitaxial relationship of this heterostructure was [110]BaTiO₃//[110]SrTiO₃//[010]Ti${}_{2.5}$O₃//[001]GaAs and the in-plane epitaxial relationship was determined to be [110]BaTiO₃//[110]SrTiO₃//[100]Ti${}_{2.5}$O₃//[110]GaAs from RHEED and XRD results. In addition, we found that the inter-diffusions of Ga and As atoms from GaAs substrate to oxides films were prevented greatly by the SrTiO₃/Ti${}_{2.5}$O₃ passivation layer. Using the Gibbs free energies of formations equations, we explained that the Ga atoms couldn’t diffuse through Ti-oxides at Ti${}_{2.5}$O₃/GaAs interface. Our work provided an effective measurement to develop the BTO application in the photovoltaic field.