SrBi4Ti4O15 Research Articles

Microstructure and ferroelectric properties of MnO2-doped bismuth-layer (Ca,Sr)Bi4Ti4O15 ceramics

We have studied the microstructures and ferroelectric properties of MnO2-doped bismuth-layered (Ca,Sr)Bi4Ti4O15 (CSBTM). The piezoelectric coefficient, dielectric loss, mechanical quality factor, and the P-E hysteresis loop measurements indicate that Mn ions entered both the A and B sites of the pseudoperovskite-layered structure, creating “soft” and “hard” doping effects simultaneously. Scanning electron microscopy and energy dispersion spectroscopy showed that the platelike grains in CSBTM ceramics become larger with the increase of MnO2 additive, and Mn ions are found inside the grains as well as in the grain boundaries. The lattice parameter, room-temperature dielectric constant, and the Curie temperature do not vary with MnO2 additive. We conclude that the Mn3+ ions play a critical role in the effects of soft and hard behaviors since it can enter both the A and B sites of the perovskite structure.

Effects of processing methods on texture development and densification in SrBi4Ti4O15 ceramics

This paper deals with the effects of preparation methods on the texture development and densification in textured SrBi4Ti4O15 (SBT) ceramics. The specimens were prepared by the oriented consolidation of anisotropic particles (OCAP), templated grain growth (TGG) and reactive templated grain growth (RTGG) methods. The specimens with extensive texture were obtained by all methods except for TGG with small template and large matrix particles. The origin of extensive texture development was the growth of aligned platelike particles. A characteristic of microstructure was the formation of colonies, in which platelike grains contacted face-to-face. The size of colonies was dependent on the preparation method, and determined the size of pores between colonies, which had a large effect on the sintered density. The OCAP and RTGG methods gave the green compacts composed of only platelike particles and large colonies and pores formed during sintering. The TGG method gave the green compacts composed of platelike and equiaxed particles and prevented the formation of large colonies and pores during sintering. Thus, the dense, highly-textured SBT ceramics were obtained by the TGG method.

Effect of Dy-doping on the properties of Sr2Bi4Ti5O18 ferroelectric ceramics

Ferroelectric Sr2Bi4-xDyxTi5O18 (SBDT-x, x= 0—0.20) ceramic samples were prepared using the conventional solid-state reaction method. x-ray diffraction patterns (XRD) of SBDT-x ceramics show that doping with a small amount of Dy does not change the crystal structur e of Sr2Bi4Ti5O18 (SBTi). Their Curi e temperature (Tc) and dielectric loss (tanδ) decrease with Dy dopin g amount. The remnant polarization (2Pr) of SBDT-x increases at first , then decreases with increasing of Dy content. When Dy content is 0.01, the 2Pr reaches a maximum value of 20.1 μC·cm-2. The variation of 2Pr for SBDT-x relates to space charge density, internal strain an d structure distortion. (Bi2O2)2+ layer acting as an insulating layer and space charge storage plays an important role in their ferroelectric properties in BLSFs. The incorporation of doping ions into (Bi2O2)2+ layer may destroy its original function and deteriorate the ferroelectric property.

Fabrication and Optical Properties of SrBi4Ti4O15/BaBi4Ti4O15 Graded Ferroelectric Thin Films

SrBi4Ti4O15 (SBTi) and BaBi4Ti4O15 (BBTi) thin films as well as SBTi/BBTi graded thin films with gradients in composition were prepared by sol-gel technique. A special heating treatment procedure was employed in this study to form the uniform composition gradients at the temperature below 850°C. The smooth graded thin films were obtained by rapid thermal annealing (RTA) at 750°C for 10 min and then annealing at 800°C for 60 min. The microstructural evolution of SBTi, BBTi and SBTi/BBTi graded films and their optical properties were studied. The band edge absorption of SBTi/BBTi graded thin films is between that of BBTi and SBTi in the wavelength 250 nm–400 nm from the results of spectrophotometric measurements of the transmittance. The band gap energy of SBTi/BBTi graded film is found to be 4.10 eV, which is between that of BBTi (3.59 eV) and SBTi (4.44 eV). It indicates that the structure of the graded thin films will affect the band gap energy and optical absorbancy of this material. Annealing conditions also have a great influence on the optical properties of graded thin films. It is found that the impurity absorption beyond the intrinsic absorption appears in the graded films, and the impurity absorption peak blue-shifts with the increase in the annealing time.

Ferroelectric Properties of MBi4Ti4O15 (M = Sr, Pb, Ca) Thin Films

Among the ferroelectric bismuth layered perovskites belonging to Aurivillius family, the MBi4Ti4O15 (MBT15, M = Sr, Ca, Pb) thin films have been fabricated by a chemical solution deposition technique, and their structures and ferroelectric properties were investigated in this work. The SrBi4Ti4O15 (SBT15) film fabricated on IrO2 presented the highest remanent polarization (Pr) among the films in this series. It demonstrated a saturated hysteresis loop at 5 V with Pr of 19 μ C/cm2 and coercive field (Ps) of 116 kV/cm. The PbBi4Ti4O15 (PBT15) thin films were selectively controlled in c-axis and off-c-axis orientation on Pt layer by adjusting the annealing condition. The off-c-axis oriented PbBi4Ti4O15 film demonstrated considerably higher Pr (8.7 μ C/cm2) than that of c-axis oriented film (3.7 μ C/cm2). Regardless of grain orientation, however, PBT15 films were not fatigued up to 1010 cycles under 9V application. The CaBi4Ti4O15 (CBT15) thin films were also produced on Pt and IrO2 electrode, respectively, by controlling the annealing condition. The CBT15 film on IrO2 presented higher Pr (∼10.8 μ C/cm2) than that of film (∼ 6.7 μ C/cm2) on Pt. † Present address: Samsung Advanced Institute of Technology, P.O. Box 111, Suwon 440-600, Korea

Study of properties of lanthanum doped SrBi4Ti4O15 ferroelectric ceramics

Ceramic samples SrBi4-xLaxTi4O15 (x =0.00, 0.10, 0.25, 0.50, 0.75, 1.00), have been prepared by solid-state reaction method. T heir structure was analyzed by x-ray diffraction, and their dielectricity and fe rroelectricity were measured. It is found that La-doping does not change the cry stal structure of SrBi4Ti4O15. The remnant pola rization (2P4) in creases at first, then decreases with the increase of La content. The 2P4 reaches a maximum value of 24.2 μC·cm-2, when x is 0.25. The c oerc ive field of SrBi3.75La0.25Ti4O15 is 60.8 kV·cm-1 . The 2P4 increases by about 50% and the Ec decrease s near 25%, compa red with these of SrBi4Ti4O15. Obviously, the f erroelectricity of SrBi 4Ti4O15 is improved by lanthanum doping. The te mperature of p hase transition (Tc) decreased with La cloping. The Tc of SrBi3.75La0.25Ti4O15 is 451 ℃. When x=0.75 and 1.00, the SrBi4-xLaxTi4O15 exhibit the typical characteristics of relaxor ferro electrics.

Thickness-Shear Vibration Mode Characteristics of SrBi4Ti4O15-Based Ceramics

Dielectric and piezoelectric properties have been investigated in bismuth layer-structure compounds SrBi4Ti4O15 (SBT) and BaBi4Ti4O15 (BBT)-based solid solutions. Lanthanum-substituted and manganese-added SBT and BBT form solid solutions for all levels of Ba substitution. The Curie temperature and coercive field strength decrease monotonously with the amount of Ba substitution. The mechanical quality factor, Qm, of the thickness-shear vibration mode also decreases. The value of elastic compliance increases with the amount of Ba substitution, but conversely its temperature dependency decreases.

Ferroelectric properties of Sr2Bi4Ti5O18 thin films

Bi-based layered ferroelectric thin films of Sr2Bi4Ti5O18 (SBTi) were prepared by pulsed-laser deposition. The c-axis-oriented SBTi films were grown on SrRuO3 seeded Pt/TiO2/SiO2/Si substrates while polycrystalline SBTi films were grown on Pt/TiO2/SiO2/Si substrates. The measurements of ferroelectricity revealed that the direction of spontaneous polarization was not along the c axis since the polarization of c-axis-oriented films was much less than that of randomly oriented films. There was no significant degradation of switchable charge at least up to 1011 cycles for the randomly oriented films, suggesting that, even with Ti which was widely accepted to contribute to the fatigue of Pb(Zr, Ti)O3, SBTi showed superior fatigue characteristics. The randomly oriented films also showed excellent retention characteristics after 105 s.

Piezoelectric Properties of SrBi4Ti4O15-Based Ceramics

Piezoelectric properties of lead-free bismuth layer structure oxide, SrBi4Ti4O15 (SBT) based ceramics, were studied. By means of La substitution and Mn addition, the maximum value of Q (Qmax ) between resonant frequency and anti-resonant frequency was larger than that of SBT. These materials could be utilized in practical applications as substitutes for lead titanate based ceramics (PT) and lead zirconate titanate based ceramics (PZT) which are used mainly in resonators. The reason for the higher Qmax value was identified by microstructual analysis as being due to the absence of a defect structure.

Electrical Conductivity of Piezoelectric Strontium Bismuth Titanate Under Controlled Oxygen Partial Pressure

AbstractHysteresis free and linear piezoelectric behavior of SrBi4Ti4O15 (SrBIT) is very promising for precise sensors/actuators devices. Despite a quite low longitudinal piezoelectric coefficient (around 15 pC/N), its elevated ferroelectric phase transition temperature (540°C) allows its use above 300°C. Electrical conductivity at such temperatures should be kept as low as possible in order to avoid loss of piezoelectric properties or charge drifts. Under reducing conditions, however, the electrical conductivity may change considerably. The electrical conductivity of SrBi4Ti4O15 (SrBIT) has been measured under controlled oxygen partial pressure at elevated temperatures (700-900°C) from 1 atm down to 10−15atm. From 1 atm down to 10−15 atm pO2, above 700°C, the conductivity of SrBIT exhibits a -1/4 slope in log-log scale indicating n-type conductivity and an impurity controlled oxygen vacancy concentration. A conductivity minimum is observed around 0.2 atm for undoped SrBIT at 800°C. Acceptor doping (Mn) raises the minimum and flattens the conductivity curve with slope around -1/10 at 700°C, and -1/6 at 900°C. Ionic conductivity and defect ionization are discussed to account for this. Preliminary results indicate the possibility of a large, pO2 independent, region, down to 10−15atm pO2. The ionic transport number was found to be 0.42 at 800°C for undoped SrBIT and 0.75 for Mn doped SrBIT. The activation energies of undoped (1.35 eV) and Mn doped (1.44 eV) samples are close to each other as expected for a common mechanism