Formation Of Ferroelectric Phase Research Articles

Enhanced Functional and Structural Characteristics of Poly(vinylidene-trifluoroethylene) Copolymer Thin Films by Corona Poling

Electrical poling is of much interest for the enhancement of polarization properties of ferroelectric materials such as poly(vinylidene-trifluoroethylene) [P(VDF-TrFE)] in applications ranging from memory devices to piezoelectric actuation. Here, we report the changes in dielectric and optical properties correlated with structural modification of P(VDF-TrFE) thin films ( thickness) subjected to corona poling at low voltages under various thermal conditions. Enhanced crystallinity of hot-poled samples was observed independent of thermal history and crystalline structure, indicating the absence of recrystallization during poling. Absorption measurements confirmed the ordered structure in hot-poled samples due to the permanent orientation of the dipoles and higher crystallinity, thus resulting in increased and long-retained capacitance of the ferroelectric P(VDF-TrFE) capacitor device from high frequency - characterization. X-ray photoelectron spectroscopy further confirmed the shifting of C and F core orbitals to higher binding energy is related to formation of more ferroelectric phases by corona poling.

Phase diagram and dielectric behavior of Ba0.6Sr0.4TiO3 thin films grown on orthorhombic substrates

Abstract Using Landau–Devonshire (LD)-type phenomenological model, we investigate the phase diagrams and dielectric behaviors of single-domain single-crystal Ba 0.6 Sr 0.4 TiO 3 films deposited on orthorhombic substrates. An anisotropic strain factor is introduced to quantitatively calculate the effects of anisotropic in-plane misfit strains. Investigation indicates that anisotropic strains play a crucial role on formation of stable ferroelectric phases and dielectric properties. The anisotropic strains induce tetragonal phases which only contain one in-plane spontaneous polarization component. These phases do not exist in BST films of the same composition under isotropic strains. Moreover, permittivity and tunability of films can reach to maximum when the corresponding spontaneous polarization component disappears at the boundaries of structural phase transition.

Formation of ferroelectric phases in KNbO3 and other niobates with perovskite structure

The Curie-Weiss temperatures T CW of NaNbO3 and AgNbO3 are determined for the first time by extrapolating the temperature dependence of the reciprocal permittivity from the cubic phase. It is established that the values of T CW of ANbO3 perovskites (A = Na, Ag, K) are practically equal, i.e., that the cubic phases of all the compounds are potentially unstable to an almost equal extent with respect to polarization. From an analysis of the EXAFS spectra of the NaNbO3 and KNbO3 cubic phases, it follows that the potential-energy surfaces of the Nb cation in both compounds are similar and exhibit eight minima shifted by 0.16 and 0.19 A, respectively, from the oxygen-octahedron center along the [111]-type directions. Based on these facts, it is inferred that the ANbO3 instability with respect to the occurrence of polarization is due to the tendency of the Nb cations to be ordered over the eight minima and that the phase transitions induced by this instability are of the order-disorder type. A statistical model capable of describing the sequence of ferroelectric phase transitions occurring in KNbO3 and in (Ba, Sr)TiO3 is proposed and studied.

Effect of the level of the addition of Pb(Y0.5Nb0.5)O3 on the structure, microstructure and ferroelectric properties of PZT(53/47)

In this work an attempt is made to study [Pb(Zr0.53Ti0.47O3)O3]1-X-[Pb(Y0.5Nb0.5)O3]X system with x = 0.0125, 0.025, 0.05, 0.075 and 0.1. It was shown that there is limited solid solubility (2.5 mol%) of Pb(Y0.5Nb0.5)O3 (PYN) in PZT (53/47). The substitution of PYN gave rise to the reduction of the volume of PZT’s unit cell. For the samples doped above this level of PYN, an extra phase comprising of Y3+, Zr4+ and Ti4+ cations were detected based on EDS-SEM and XRD analysis and also a structural shift towards a rhombohedral phase was noticed for the main PZT phase. Further, the addition of PYN up to 2.5 mol% was seen to increase the room temperature relative permittivity and d33 parameter. However, these parameters declined for the samples substituted with more than 2.5 mol% PYN due to the formation of non ferroelectric extra phase.

Development of Nonvolatile Memory using Well-Ordered Ferroelectric Linear Molecules

ABSTRACTFerroelectric vinylidene fluoride (VDF) molecular films were fabricated by simple vacuum evaporation method, and the ferroelectric properties and its fatigue were investigated. Formation of ferroelectric phase in VDF oligomer with low molecular weight is favored at low substrate temperature around -150°C. The well-ordered VDF oligomer thin films exhibit a lager value of remanent polarization(130mC/m2) than that of Poly(VDF). Fatigues of polarization reversal can be performed over 10∧5 cycles. The VDF oligomer films can be one of candidates for disposable nonvolatile memory with unique features such as flexible, wide areas and low cost processing.

Tuning the Tunability in Epitaxial Barium Strontium Titanate Film via Internal Stresses

ABSTRACTThe tunability of epitaxial barium strontium titanate films is analyzed theoretically for the first time using a modified phenomenological Landau-Devonshire approach taking into account the formation of unusual ferroelectric phases that cannot form in bulk and single-crystal ceramics. It is shown that enhanced tunability can be achieved by adjusting the misfit strain especially in the vicinity of a structural phase transformation. The internal stresses in epitaxial films as characterized by the misfit strain can be controlled by changing the substrate material and/or varying the film thickness. The latter is due to the possibility of stress relaxation by formation of misfit dislocations that relieve epitaxial stresses at film growth temperature. Based on the thermodynamic model, we provide quantitative estimations of tunability of (001) Ba0.5Sr0.5TiO3 films on (001) LaAlO3 (LAO) and SrTiO3 (STO) as a function of film thickness. The analysis indicates that films on STO substrates should be as thick as possible in order to achieve optimum tunability. To obtain maximum tunability on LAO substrates, the thickness of films should be as close as possible to a critical film thickness (∼120 nm).

Structure and electrical properties of SrBi 2Ta 2O 9 thin films annealed in different atmosphere

Layered ferroelectric SBT films were prepared on Pt/TiO 2/SiO 2/Si substrates by metalorganic decomposition. The films were annealed in vacuum, argon, nitrogen and different ratios of N 2/O 2 atmospheres to investigate the effect of annealing atmosphere on structural and ferroelectric properties of the films. X-ray diffraction, scanning electron microscopy and some electric measurements were used to determine the structure, morphology and ferroelectric properties of the films. It was found that oxygen plays an important role in SBT ferroelectric phase formation and has great effect on morphology and electric properties of the films.

Effects of B-site ordering/disordering in lead scandium niobate

Effects of disordering of Sc3+ and Nb5+ in the relaxor ferroelectrics Pb(Sc1/2Nb1/2)O3 (PSN) were investigated by means of measurements of x-ray scattering and dielectricity. Results on the diffuse scattering from ordered PSN indicate lattice instabilities at the and M points near 353 K, and these were expected to cause the formation of ferroelectric (FE) and antiferroelectric (AF) phases. The freezing behaviours are slightly diffuse because of the partitioning of the thermal energy to the two modes, but yet of the type characteristic of normal soft-phonon modes. The results of the dielectric constant measurement under an alternating-current field indicated a highly polydispersive dispersion and a significant temperature dependence of the relaxation frequency. These unusual results imply a competing interaction between the two lattice instabilities. The x-ray work on disordered PSN shows `diffuse' transition behaviours at the two points. It is suggested that this feature originates from lattice relaxation through the softening of the two modes. The distortions are self-accommodated in atomic displacements at the M point, and analysis of the intensities suggests that the displacement pattern has the form of an AF distortion. During the FE freezing, the coexisting FE and AF regions may give rise to a dipole-glass state, and this is thought to cause relaxor behaviours through frustration between the two states.

Film structure and ferroelectric properties of in situ grown SrBi 2 Ta 2 O 9 films

Ferroelectric SrBi2Ta2O9 (SBT) films were grown by pulsed-laser deposition (PLD) at different substrate temperatures and fluences. A correlation between film structure and ferroelectric properties is established. The dielectric function e′ of thin SBT films shows a Curie–Weiss behavior well below the peak temperature Tmax and relaxor-like behavior in the vicinity of Tmax. Domain walls have a strong influence on the dielectric and ferroelectric properties and on the polarization fatigue of SBT films below 100 °C. The formation of ferroelectric phases is favored at lower substrate temperatures by incorporating Bi2O3 template layers into the structure.

C-Axis Oriented Ferroelectric thin Films of PbtiO3 on Silicon Substrate by Pulsed Laser Ablation

ABSTRACTWe are reporting the successful deposition of single phase c-axis oriented ferroelectric thin films of PbTiO3 on Si (100) by pulsed laser deposition. It is shown that the formation of non ferroelectric Pb2Ti2O6 phase at the interface could be avoided by raising the substrate temperature sufficiently high. The film deposition conditions are optimized so as to achieve better ferroelectric properties.