Properties Of BaTiO3 Research Articles

Theoretical investigation on the structure and electronic properties of barium titanate

The structure and electronic properties of the cubic barium titanate (BaTiO 3) have been calculated using the different density functional theories (DFT) and various pseudopotential methods. This paper investigated the performance of the different DFT and various pseudopotential methods in calculating the crystal structure and properties of BaTiO 3. The calculation results show that GGA/PW91 and ultrasoft pseudopotential methods are good for predicting the electronic structure and properties of BaTiO 3. The results also indicate that BaTiO 3 is indirect semiconductor, ionic bond forms between Ba atom and TiO 3 group and covalent bond forms between Ti and O atoms in the unit cell. The calculated electronic structure, energy band structure and density of states (DOS) of BaTiO 3 are in good agreement with the theoretical and experimental results.

Use of Raman spectroscopy to determine the site occupancy of dopants in BaTiO3

Chemical doping is one of the major methods by which the properties of BaTiO3 are modified to induce various device characteristics. Doping strategies are generally separated into iso- and alio-valent (donors and acceptors) and into A- and B-site species within the perovskite structure. The A1g octahedral breathing mode at ∼800 cm−1 in BaTiO3 is Raman inactive for compositions with single B-site species. However, this mode becomes Raman active if more than one B-site species is present, including titanium vacancies, VT′′′′. Moreover, the relative intensity of the A1g breathing mode is qualitatively related to the concentration of the species replacing Ti in the B-site. This article illustrates some clear cases where the A1g octahedral breathing mode can be utilized to verify the site occupancy of dopants in BaTiO3 when used in conjunction with more conventional indirect methods such as x-ray diffraction (Vegard’s Law) and dielectric measurements as a function of temperature.

Study of Pb(Zr0.65Ti0.35)O3(PZT(65/35) doping on structural, dielectric and conductivity properties of BaTiO3(BT) ceramics

x)BaTiO3-xPZT(65/35) ceramics were prepared by high temperature solid state reaction technique. Structural properties of the compounds were examined using an X-ray diffraction (XRD) technique to confirm the formation of phase at room temperature. Detailed studies of dielectric properties of (1−x) BaTiO3-xPZT(65/35) for all compositions were in temperature range 30- 200 o C reveal that the compound have transition temperature well above at the room temperature. While pure BaTiO3 ceramics exhibited a sharp phase transformation expected for normal ferroelectrics, phase transformation behavior of the (1−x) BaTiO3-xPZT(65/35) solid solutions became more diffuse with increasing PZT(65/35) contents. The diffusivity of the dielectric peaks in the compound exhibited the values between 1 and 2 where the higher value indicates the greater disorder in the systems. This was primarily evidenced by an increased broadness in the dielectric peak, with a maximum peak width occurring at x = 0.5. The temperature dependence of ac conductivity indicated that the electrical conductivity decrease above T C on increasing the PZT(65/35) contents. This increase in the conductivity is attributed to the increase in polarizability of the materials around Tc, due to oxygen vacancies. Copyright © 2011 VBRI press.

Effect of working pressure on the properties of BaTiO 3–CoFe 2O 4 composite films deposited on STO (100) by PLD

The BaTiO 3–CoFe 2O 4 (BTO–CFO) composite films were grown on SrTiO 3 (STO) (100) substrates at 750 °C under various working pressures by pulsed laser deposition. The composite film grew into a supersaturated single phase at the working pressure of 10 mTorr, BTO and CFO (00 l) oriented hetero-epitaxial films on STO (100) at 100 mTorr, and a polycrystalline composite film at 500 mTorr. The slow growth rate at high working pressure led to the phase separation in the composite film. The CFO was compressively strained along out-of-plane due to the lattice mismatch with the BTO matrix phase. The BTO–CFO composite film grown at 100 mTorr showed reversible switching of ferroelectric polarization and magnetic hysteresis with strong magnetic anisotropy.

Structure and dielectric properties of BaTiO3–BiScO3 ceramics sintered by CaF2–4LiF aids

The effect of CaF2–4LiF (1–5 mol.-%) on the phase structure, microstructure and dielectric properties of 0·9BaTiO3–0·1BiScO3 (0·9BT–0·1BS) ceramics has been investigated. The 0·9BT– 0·1BS with CaF2–4LiF dopant ceramics sintered at 1100°C show a pure perovskite structure. Results show that CaF2–4LiF dopant can improve the sintering ability of 0·9BT–0·1BS ceramics when CaF2–4LiF content is below 3 mol.-%. The ceramics with 3 mol.-%(CaF2–4LiF) sintered at 1100°C exhibit a high permittivity, low dielectric loss as well as flat ϵ′ v. temperature curve indicating a favourable temperature stability, which are listed as follows: ϵ′25°C=1483, tan δ25°C=0·00309, Δϵ′/ϵ′25°C ≤ ± 13% at 100 kHz, in the temperature range from –55 to 150°C. This low sintering temperature allows using relatively inexpensive internal electrodes in the production of future capacitors.

Sensitivity analysis and optimization of interatomic potential parameters for perovskites

An effective interatomic potential is crucial for molecular dynamics simulations. In this paper, a more effective optimization method for potential parameters is proposed. Sensitivity analysis is used to find the key parameters affecting the structure and properties most in all the potential parameters. The secondary parameters are ignored, and the dimension of the optimization is reduced. The genetic algorithm is adopted to optimize the key parameters. The results show that the structure and physical properties of BaTiO3 and SrTiO3 simulated by the optimized potential are more close to experimental data.

Strain effect on ferroelectric behaviors ofBaTiO3 nanowires: a molecular dynamics study

In this paper, a molecular dynamics method is utilized to investigate the strain effect onthe polarization distribution, piezoelectric coefficient, and hysteresis behaviors ofBaTiO3 nanowires. The axial polarization changes almost linearly with the strainover a relatively large range, and the ferroelectricity vanishes under a criticalcompressive strain. With the nanowire becoming thicker, the piezoelectric coefficientincreases, and approaches its counterpart for bulk material when the diameter islarger than 2.4 nm. It is also revealed that a pre-tension strain can induce theemergence of a stepwise hysteresis loop while a pre-compression strain can lead tothe disappearance of the stepwise shape. Furthermore, the strain effect and sizeeffect are found to play some equivalent roles in the ferroelectric properties ofBaTiO3 nanowires.

Dynamical behavior of the phase transition of strained from atomistic simulations

Abstract Using an atomistic shell model we study the temperature dependence of the ferroelectric properties of BaTiO 3 under biaxial compressive strain applicable to growth on perovskites substrate. Molecular dynamics simulations show a “ r → c → p ” sequence of phase transitions when temperature is increased, and the absence of an “ ac phase”. The first-order paraelectric-to-ferroelectric phase transition presents in bulk changes to a second-order one as a consequence of the in-plane constraint imposed by the mechanical boundary conditions. From the tetragonal ferroelectric c phase, the transition takes place in a finite range of temperature where the lattice parameter normal to the plane keeps approximately constant until T c is reached. Analysis of the local polarization behavior reveals an order–disorder dynamics as the dominant mechanism of the transition.

Thickness dependence of dielectric properties in BaTiO 3 films fabricated by aerosol deposition method

In order to prepare embedded planar decoupling capacitors with high capacitance density, we attempted to fabricate BaTiO 3 thin films on Cu substrates at room temperature by employing aerosol deposition method (ADM). Their thickness range was 0.2–1.5 μm. From the measurement of the magnitude and phase of their impedance by a vertical type, it was confirmed that BaTiO 3 thin films acted like conductors or dielectrics in the thickness range of 0.8–1.0 μm. In this thickness range, we supposed that their high leakage currents resulted in the problems of interfaces between BaTiO 3 thin films and Cu substrates or the quality of BaTiO 3 films themselves. So, the magnitude and phase of impedance of BaTiO 3 thin films deposited on glass substrates and Cu substrates to remove the problems of interfaces were measured by a horizontal type. As a result, all BaTiO 3 thin films deposited on glass substrates became dielectrics. However, some BaTiO 3 thin films with below 0.8 μm deposited on Cu substrates acted like conductors in this thickness range. Consequently, it could be suggested that the major causes were problems of interfaces between BaTiO 3 thin films and Cu substrates.

Properties of BaTiO 3 synthesized from barium titanyl oxalate

In order to enhance the tetragonality of BaTiO 3 derived from barium titanyl oxalate (BTO), various treatments were carried out by considering the thermal decomposition mechanism of BTO in air. A multi-step heat treatment process and the addition of carbon black, as a particle growth inhibitor, were effective in increasing the tetragonality, whilst maintaining a particle size smaller than 200 nm. The synthesized BaTiO 3 powder with a mean particle size of 177 nm showed a tetragonality and K-factor of 1.0064 and approximately 3, respectively.

Study of nanostructural behavior and transport properties of BaTiO3 doped vanadate glasses and glass–ceramics dispersed with ferroelectric nanocrystals

Abstract Nanostructural behavior and electrical properties of BaTiO 3 -(100− x )V 2 O 5 glasses (where x =35, 40, 45 and 50 mol%) and their corresponding nanocrystalline glass–ceramics were studied. Scanning electron microscopy (SEM) of quenched glasses, confirm the amorphous nature of the glasses present. Also, the overall features of X-ray diffraction (XRD) confirm the amorphous nature of the present glasses. Transmission electron micrograph (TEM) and XRD of the corresponding heat treated sample indicate nanocrystals with a particle size of 20–35 nm. It was found that density ( d ) increases gradually with the increase of the BaTiO 3 content in the nanocrystalline glass–ceramics. It is observed that the conductivity of the nanocrystalline glass–ceramics is higher than that of the corresponding glassy phase. The high conductivity of these nanocrystalline glass–ceramics is considered to be due to the presence of nanocrystals with a particle size of 20–35 nm. This is attributed to the formation of extensive and dense network of electronic conduction paths which are situated between V 2 O 5 nanocrystals and on their surface. The electrical conductivity of this system can be fitted with Mott's model of nearest neighbor hopping at high temperature. From the best fits, reasonable values of various small polaron hopping (SPH) parameters are obtained. From dielectric permittivity of the as-cast glass samples, no ferroelectric behavior can be observed. Also, the dielectric permittivity ( e ) values of these glasses are found to be very high compared to familiar vanadium containing glasses. By annealing the glass system around 450 °C for 1 h in air, nanocrystalline BaTiO 3 phase precipitates and the corresponding nanocrystalline glass–ceramics showed average broad peak around 352 K in the dielectric permittivity ( e ). It is interesting to note that pure nanocrystalline BaTiO 3 phase with average particle size less than 100 nm also shows ferroelectric phase transition around this temperature as predicted from the dielectric permittivity measurements. This observation of these glass–ceramics nanocrystals can be utilized to control BaTiO 3 particle size and hence transition temperature by proper adjustment of annealing time and BaTiO 3 content. Such a feature can be used for industrial applications where the shape of the application article is a necessary requirement.

Non-Linear Properties of BaTiO3 above T C

Although numerous papers on physical properties of the BaTiO 3 crystal can be found in literature, there is a lack of tentative studies of its properties in temperature range close to but above T C . That is why investigations of temperature dependence of the dielectric properties, electrostrictive strain and thermal expansion have been undertaken. Results obtained point to non-linear behaviour of all these properties even tens degrees above T C . Especially the non-linear thermal expansion, first time measured in detail for BaTiO 3 above T C , implies the existence of micro/nano-polar regions whose temperature stability and sizes are responsible for temperature hysteresis above T C .

Crystal structure and properties of BaTiO3–(Bi0.5Na0.5)TiO3 ceramic system

(1 − x)BaTiO3–x(Bi0.5Na0.5)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 (Bi0.5Na0.5)TiO3 (BNT) content. The Curie temperature, Tc, 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, d33, 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 d33 together with the electromechanical coupling factors, kt, 19.8% and kp, 15.8%, were obtained when BNT was 93 mol%.

X-Ray Absorption Spectroscopy Study of Ba1-xSrxTiO3 (x = 0.0-0.2) at the Ti-K and Ba-LIII Edges

Barium titanate, BaTiO3 is a significant material for electronic components. It was known that Sr2+ substitution on Ba ion can strongly modify ferroelectric properties of BaTiO3 but the structural change has not been fully understood. An X-ray absorption spectroscopy at the Ti K-edge (4966 eV) and the Ba LIII-edge (5247 eV) was employed to investigate the structure of Ba1-xSrxTiO3 (BSTO) with 0<x<0.20. Results suggested that Ba2+ did not change its position with Sr2+ substitution. On the other hand, Ti4+ atoms gradually displaced as Sr2+ is increased.

Synthesis of BaTiO3 by soft chemistry routes

In this paper we report a comparison concerning the properties of BaTiO3 (BTO) ceramics obtained by two soft chemical routes, modified Pechini method and thermal decomposition of oxalate-based precursor. XRD data show the formation of single phase BaTiO3 with tetragonal symmetry when the polymeric citrate-based precursor was annealed at 850 °C, 2 h. In the case of oxalate based-precursor, longer thermal treatment is required to obtain BaTiO3 free of any secondary phases. For BaTiO3 powders prepared by modified Pechini method, TEM and SEM investigations revealed the obtaining of uniformly sized particles forming spherical agglomerates inside large, non-uniform and partially sintered aggregates. The powders synthesized via oxalate route show particles of various sizes, with the same tendency of spherical agglomerates formation, but unlike the modified Pechini synthesis, more uniform and smaller aggregates with well-defined hexagonal-like shape were noticed. The relative permittivity values of 6,478 and 5,088 at Curie temperatures of 127 and 130 °C and low dielectric losses (tan δ = 0.012) at room temperature were obtained for ceramic samples synthesized via Pechini method and oxalate route, respectively.

Physical and dielectric properties of BaTiO3–fluoride–glass systems for nitrogen-fireable embedded capacitors

BaTiO3-based dielectrics containing the selective additive combinations from Pb-free glasses and fluoride compounds such as AlF3, BaF2, CaF2, LiF and ZnF2 were studied mainly for a potential N2-fireable embedded capacitor in printed circuit board with Cu metallization. The physical and dielectric properties, such as dielectric constant (k), loss tangent (tanδ) and Tc, strongly depended on the choice of additive combination. A bismuth borosilicate glass was most promising in terms of the degree of densification and dielectric constant. The samples containing LiF and ZnF2 and sintered at 950 °C looked most beneficial in that these additives produced high k of >1,200 and low tanδ of < 0.022 at room temperature regardless of sintering atmosphere. As an example, the 95BaTiO3–2LiF–3(Bi borosilicate) sample exhibited k ~ 1,340 and tanδ ~ 0.022 at room temperature when fired at 950 °C in N2.

Optical properties of BaTiO3 thin films: Influence of oxygen pressure utilized during pulsed laser deposition

The crystallographic properties of BaTiO3 thin films, grown by pulsed laser deposition on MgO substrates, were found to be strongly influenced by the oxygen pressure used during growth. Low pressure grown films were c-oriented while increasing oxygen pressure produced films with preferred a-orientation. The crystal reorientation resulted in the shift of optical birefringence from +0.04 to −0.025 with low levels of birefringence in films possessing low tetragonal distortion. Mach-Zehnder electro-optic waveguide modulators were fabricated to characterize the electro-optic properties of the deposited films and to evaluate the suitability of these films for planar optical applications. An effective electro-optic coefficient of 23 pm/V was obtained for a c-axis oriented film near the crystal c→a reorientation point.

Microstructure and Electrical Properties of BaTiO&lt;sub&gt;3&lt;/sub&gt;-Based PTC Ceramics Prepared from Nanopowders

Dense PTC ceramics were prepared with BaTiO3 nanopowders synthesized by hydrothermal method. BaCO3 and Ti(OC4H9)4 were used as barium and titanium sources, and Y(NO)3·6H2O as the donor dopant respectively. The average grain size of the powders obtained after hydrothermal treatment at 160°C for 9h was about 30nm with cubic structure. Mn(NO3)2 was introduced to the as-prepared nanopowders in order to improve the PTC effect. After sintered at 1280°C, the PTC ceramic samples exhibited sufficient resistance jump ratio(1.086×103) around Curie temperature, the density of which was 5.81g/cm3(96.5% of the theoretical density).

Effect of fluorine doping on the microstructure and electrical properties of barium-titanate-based ceramics

The effect of partial fluorine substitution for oxygen on the properties of BaTiO3 has been studied using thermogravimetry, x-ray diffraction, electron microscopy, complex impedance measurements, and diffuse reflectance spectroscopy. The results indicate that partial fluorine substitution for oxygen influences the composition range of positive temperature coefficient of resistance behavior in ceramics with heterovalent substitution of lanthanum on the barium site.

A strong correlation of crystal structure and Curie point of barium titanate ceramics with Ba/Ti ratio of precursor composition

A series of barium titanate powders were synthesized from precursors BaCO3 and TiO2 with Ba/Ti ratio ranged from 0.96 to 1.04. For the ceramics sintered at 1300 °C for 2 h, with increasing Ba/Ti ratio from 0.96 to 1.04, the tetragonal distortion of perovskite barium titanate phase was decreased continuously and the Curie point was decreased monotonously from 122.9 to 98.0 °C. At the same time, the content of secondary phases was very low. This correlation of crystal structure and Curie point of barium titanate ceramics was explained by composition variation of the perovskite phase itself rather than by the influence from secondary phases. Due to very controversial results reported by different groups, it was proposed that BaTiO3 has some different states with different solubilities for BaO and TiO2. Further investigations should be conducted on the preparation and the properties of BaTiO3 with much BaO or TiO2 dissolved.