Dependence Of Ferroelectric Properties Research Articles

Synchrotron based x-ray absorption spectroscopy investigation and temperature dependent ferroelectric properties of Ni doped BaTiO3 nanostructures

In this report, the local structure geometry of BaTi1-xNixO3 (0.0 ≤ x ≤ 0.06) ceramics has been studied through synchrotron based x-ray-absorption spectroscopy, measured at the Ti K, Ba L3 and Ni K-edges at room temperature. The x-ray absorption near edge spectroscopy (XANES) at Ti K-edge confirms the TiO6 octahedron geometry of Ti atom due hybridization between Ti(3d)-O(2p) orbitals and signifies the non-centrosymmetric nature of BaTiO3 samples. However, Ti–O off-center displacement (non-centrosymmetric) is disturbed under the effect of Ni doping as a result of oxygen vacancies formation. More interestingly, XANES studies at Ni K-edge ensure successful substitution of Ni in BaTiO3 as Ni2+ ions. Extended x-ray absorption fine structure (EXAFS) data at Ni K-edge have been fitted to estimate pertinent local structural parameters of the Ni–O, Ni–Ba, Ni–Ti and Ni–Ni shells (viz. bond lengths and disorder parameters) and it also reveal that the structural disorders around the Ti sites in the doped BaTiO3 expand with Ni doping. The mixed-valence states of titanium ion, i.e., Ti4+ and Ti3+ in the doped samples were established with the x-ray photoelectron spectroscopy (XPS). Moreover, XPS divulges the creation of oxygen vacancies due to Ni doping in BaTiO3 matrix. The complementary information about the lattice vibration is analyzed through Raman studies that approve the softening of the transverse optical (TO) mode present at 515 cm−1. The temperature dependent ferroelectric studies affirm that the ferroelectricity vanishes in the doped samples due to the decrement in the off-center displacement between the Ti4+ and O2− ions in the TiO6 octahedral geometry. Differential thermal analysis (DTA) exhibits a ferroelectric tetragonal to para-electric cubic phase transition in the pristine as well as Ni doped BaTiO3 samples.

Theoretical investigation of temperature and frequency dependent ferroelectric properties in Rochelle salt (RS) crystal

By adding cubic-order and quartic-order phonon anharmonic interactions terms with spin-spin interactions terms, extra interaction term and external electric field has been considered in two-sublattice pseudospin lattice coupled mode (PLCM) model for phase transitions and dielectric properties of order-disorder Rochelle salt (RS) crystal. Using double-time temperature Green function method, we obtain the expression for Soft mode frequency, dielectric constant and tangent loss have been obtained for Rochelle salt crystal. Numerical calculations will be performed by fitting model values of various parameters in the above expressions for RS crystal. Present theoretical results agree well with experimental results of Sandy and Jones.

Temperature dependent ferroelectric properties of Sm and Fe substituted BaTiO3

The material series with compositional formula Ba1-xSmxTi1-xFexO3 (x = 0.0025, 0.0075, 0.01) was chosen and investigated for temperature dependent ferroelectric properties. The samples in powder form were synthesized by solid state reaction method and compacted in the form of circular discs which were sintered at 1325 °C. The ferroelectric properties were investigated by recording the PE hysteresis loops of all the samples at different temperatures (at 50 Hz). Remanent polarization ‘Pr’ and Coercive field ‘Ec’ of all samples was noted from PE loops. These studies demonstrate the potential for use in applications at elevated temperatures such as in non-volatile ferroelectric memory applications.

Effect of Eu3 + doping on curie temperature and fatigue properties of Pb,La(ZrTi)O3 films

Pb0·92(La1−yEuy)0·08(Zr0·52Ti0·48)0.98O3 (PLEZT) films were prepared with varying Eu3+ concentrations (y=0.0, 0.3, 0.5 and 0.7) to study the doping effect on crystal structure and ferroelectric properties. The XRD results confirmed the formation of tetragonal perovskite structure in PLEZT with gradual increase in (110) peak intensity. The residual stress value calculated for PLZT film was (+)0.751GPa which reduces to (+)0.387GPa with increasing Eu3+ concentration. The influence of Eu3+ doping concentration on ferroelectric switching behaviour was investigated by observing the remanent polarization, spontaneous polarization and displacement current. The remanent polarization (Pr) in PLZT film increased from 8.9μC/cm2 to 13.3μC/cm2 with Eu3+ concentration which is expected due to the increase in tetragonality factor and reduction in dipolar defects in PLEZT films. A strong residual stress dependent ferroelectric properties and phase transition temperature was observed in PLZT films with Eu3+doping. The improved fatigue resistance observed in Eu3+ doped PLZT may be due to the suppression of oxygen ion vacancy.

Correlation between the macroscopic ferroelectric material properties of Si:HfO2 and the statistics of 28 nm FeFET memory arrays

ABSTRACTWith the discovery of ferroelectric hafnium oxide (FE-HfO2), the ferroelectric field effect transistor (FeFET), a long-term contender for non-volatile data storage, has finally managed to scale to the 2× nm technology node. Here for the first time, we correlate the thickness dependent ferroelectric properties of Si:HfO2 with the memory characteristics of small (56 bit) FeFET arrays. First, an electrical and structural analysis of metal-ferroelectric-metal capacitors is given. Even though possessing room-temperature deposited top electrodes, TiN / Si:HfO2 (20 nm) / TiN capacitors are showing deteriorated polarization characteristics as compared to their 10 nm Si:HfO2 counterparts. This could be attributed to an increased monoclinic phase fraction, as indicated by small-signal capacitance voltage and grazing incidence X-ray diffraction measurements. Identical Si:HfO2 thin films with thicknesses of 10 nm and 20 nm respectively, were utilized in a 28 nm high-k metal-gate CMOS flow to form small FeFET memory arrays of AND architecture. After extracting the most suitable operating conditions from erase matrix, single cell evaluation was performed by standard VP/3 program and a novel VP/3 positive-source drain erase scheme. Array cells incorporating 10 nm Si:HfO2 films showed a maximum memory window of 1.03 V whereas cells incorporating 20 nm Si:HfO2 films could reach up to 1.57 V. Moreover, in accordance to the basic material properties, the previously observed increased monoclinic phase fraction in 20 nm Si:HfO2 thin films correlate well with a reduced number of functional FeFET cells.

Effect of Zr substitution on phase transformation and dielectric properties of Ba0.9Ca0.1TiO3 ceramics

Ba0.9Ca0.1Ti1−xZrxO3 (x = 0.05, 0.07 and 0.10; BCTZ5, BCTZ7, BCTZ10) lead free ceramics were prepared by solid state reaction. The phase transitional behaviour, composition, and temperature dependent electrical properties and composition dependent ferroelectric properties were investigated. XRD analysis at room temperature and Rietveld refinement revealed a structural transformation from tetragonal to rhombohedral with enhancement of Zr content in the BCT matrix. Study of impedance spectra of these ceramics confirmed a heterogeneous electrical microstructure where the conduction and relaxation mechanisms originated from grain boundaries and grains. The ceramics depicted non Debye type of relaxation. Dielectric properties illustrated a decrease in Curie temperature and a diffused phase transition behavior with increase in Zr content. The conducting species changed from V′o to V′′o on ferroelectric phase transition in grain interiors. Saturated hysteresis loops confirmed the ferroelectric nature of the ceramics.

Frequency Dependent Ferroelectric Properties of BaZrO3 Modified Sr0.8Bi2.2Ta2O9 Thin Films

Frequency dependent ferroelectric properties were investigated in BaZrO3 (BZ) modified Sr0.8Bi2.2Ta2O9 (SBT) thin films deposited by sol-gel spin coating technique. The polarization versus electric field (P-E) hysteresis loops of pure and doped SBT films were comparatively studied for frequencies ranging from 1 to 100 kHz. It was found that the coercive field (2EC) increases and the remanent polarization (2Pr) decreases with increasing frequency. Such an increasing behavior of 2EC is associated with resistance, since domain switching consists of domain wall motion through ferroelectric material. It was found that the frequency dependent coercive field relation obeys the Ishibashi power law. Also, it was noted that the 2Pr value decreases with a logarithmic function of frequency. These frequency dependent properties are attributed to oxygen vacancies and leakage current, which are enhanced after BZ doping.

Repetition Rate Dependence of Ferroelectric Properties of Polycrystalline BiFeO3 Films Prepared by Pulsed Laser Deposition Method

Polycrystalline BiFeO3 (BFO) films on Pt/TiO2/SiO2/Si substrate have been prepared by a pulsed laser deposition (PLD) method with various repetition rates. The X-ray diffraction (XRD) pattern observes single-phase perovskite structure with a small secondary phase. While the film-thickness is increased with increasing repetition rates, the grain size increases, and the leakage current reduces. Also, good polarization versus electric field (P-E) hysteresis loops of all polycrystalline BFO films were obtained at room temperature (RT). It is seen that the polarization value (Pr ) practically remains almost constant for all the BFO films, and the coercive field (Ec ) decreases with increasing the film thickness.

Monte Carlo Investigation of Mixed Normal and Relaxor Ferroelectrics

In this work, Monte Carlo simulation was used to model the ferroelectric behavior of mixed normal and relaxor ferroelectrics using the single polarization-flip algorithm. The purpose is to investigate the dependence of ferroelectric properties on the field frequency, the temperature and the normal ferroelectric concentration in the relaxor ferroelectrics. Results obtained from both static and dynamic simulation stress the significant effect of the larger ferroelectric interaction caused by the normal ferroelectric contents. For instance, with increasing normal ferroelectric concentrations, the transition between zero and nonzero polarization phases shifts to a higher temperature due to stronger ferroelectric interaction. In addition, the stronger ferroelectric interaction also causes less polarization switching, where the hysteresis gets larger in size at low frequencies, but smaller at high frequencies. This strong ferroelectric interaction also shifts the frequency at maximum phase-lag between polarization and field signal to a lower frequency. These results are in good agreement with experiments, where applicable.

Stress Dependent Ferroelectric Properties of PZT and 0.9PZT – 0.1BLT Ceramics

P-E hysteresis loops of PZT and 0.9PZT – 0.1BLT ceramics were determined using a modified Sawyer-Tower circuit. Ferroelectric properties investigation of the PZT and 0.9PZT – 0.1BLT ceramics under stress levels in the range of 0–175 MPa was also carried out. The result showed that with increasing stress level, a reduction of remanent polarization was clearly observed. The result was interpreted in terms of non-180° ferroelectric domain switching processes and the decrease in switchable part of domains induced by stress applied to these materials.

The Dependence of Electric Properties of [Bi0.5(Na1 − x Ag x )0.5]1 − y Ba y TiO3 Ceramics on Temperature

The temperature dependence of the electric properties of lead-free piezoelectric ceramics, [Bi 0.5 (Na 1 − x Ag x ) 0.5 ] 1 − y Ba y TiO 3 , were investigated. The dependence of the dielectric properties on temperature shows that when y = 0.06 and 0.08, two anomalies of dielectric constant corresponding to the depolarization temperature (T d) and the temperature (T max) where ϵ r has the maximum value are observed. And only one dielectric loss peak corresponding to the temperature which is lower than T d for 35–50°C is observed. The dependence of ferroelectric properties on temperature shows that the remanent polarization becomes zero at T d . Moreover, the T d decreases with the increasing amount of Ag+ in this system.

Realization of Giant Piezoelectricity on k31 Mode in Pb(Mg1/3Nb2/3)O3-PbTiO3 Single-Crystal Plates

Giant k31in (1 − x)Pb(Mg1/3Nb2/3)O3-xPbTiO3 (x = 0.251∼ 0.301) (PMNT) (110) single-crystal plates with dimensions of 13L × 4.0 W × 0.25T mm was investigated by the chemical composition dependence of ferroelectric properties, impedance response on the k31 mode, P-E hysteresis loop and electric-field induced strain. The dielectric and piezoelectric measurements versus the Ti content (x) showed four groups. Giant k31 of more than 80% was obtained for x = 0.251∼ 0.293, and the maximum k31 reached 92% (x = 0.291). A mechanism for realizing giant k31 was explained by the relationships between the crystal planes, which strongly affect the direction of the spontaneous polarization and poling direction.

Effects of europium content on the microstructural and ferroelectric properties of Bi4−xEuxTi3O12 thin films

The effects of europium (Eu) content on the microstructure, fatigue endurance, leakage current density, and remnant polarization (2Pr) of Bi4−xEuxTi3O12 (BET) thin films prepared by metal-organic decomposition method at 700°C annealing temperature were studied in detail. The results showed that 2Pr (82μC∕cm2 under 300kV∕cm), fatigue endurance (2% loss of 2Pr after 9.0×109 switching cycles), and leakage current density (1×10−8A∕cm2 at 200kV∕cm) of BET thin film with x=0.85 are better than those of thin films with other contents. Additionally, the mechanism concerning the dependence of ferroelectric properties on Eu content was discussed.

Thickness dependent ferroelectric properties of BSTO thin films deposited by RF magnetron sputtering

The thickness dependence of ferroelectric permittivity of (Ba, Sr)TiO3 has been investigated. The BST films could be obtained to have a simple cubic perovskite structure, space group Pm3m, and practically c-axis epitaxial structure deposited at 800∘C. Through post-annealing process, we have improved the dielectric properties; dielectric permittivity, dielectric loss, and tunability. The change in dielectric properties before and after annealing is attributed to the change in film strain and the contraction in film lattice. As the thickness of BST films increases from 55 nm to 350 nm, the dielectric constant of BST films increases from about 100 to above 670 due to the reduction of interfacial dead layers with low dielectric constant between films and top electrodes. The dielectric loss of BST thin films decreased as the thickness increases. The existence of interfacial dead layers in a thinner film had a larger effect on the effective dielectric constant than tensile strain between the BST films and MgO substrate.

Orientation dependent ferroelectric properties in samarium doped bismuth titanate thin films grown by the pulsed-laser-ablation method

Samarium doped bismuth titanate thin films with the composition of Bi3.25Sm0.75Ti3O12 and with strong preferred orientations along the c axis and the (117) direction were fabricated on Pt∕TiO2∕SiO2∕Si substrate by pulsed laser ablation. Measurements on Pt∕BSmT∕Pt capacitors showed that the c-axis oriented film had a small remanent polarization (2Pr) of 5μC∕cm2, while the highly (117) oriented film showed a 2Pr value of 54μC∕cm2 at an electrical field of 268kV∕cm and a coercive field Ec of 89kV∕cm. This is different from the sol-gel derived c-axis oriented Bi3.15Sm0.85Ti3O12 film showing a 2Pr value of 49μC∕cm2.

Dependence of Ferroelectric Properties on Thickness of BiFeO3 Thin Films Fabricated by Chemical Solution Deposition

Bismuth ferrite (BiFeO3) thin films were fabricated by depositing sol–gel solutions on Pt/Ti/SiO2/Si(100) structures. X-ray diffraction (XRD) showed that a polycrystalline phase and also a small fraction of a secondary phase, Bi2Fe4O9, were present in the film. The nonperovskite secondary phase decreased with increasing thickness, which showed the influence of volume effects on the film. Improved leakage current density and enhanced polarization in BiFeO3 films were observed. A 400-nm-thick film showed a leakage current on the order of 10-8 A/cm2 at room temperature. The remanent polarization was approximately 90 µC/cm2 at 80 K and the piezoelectric coefficient d33 was approximately 50 pm/V.

Uniaxial stress dependence of ferroelectric properties of xPMN-(1–x)PZT ceramic systems

Effects of uniaxial compressive pre-stress on the ferroelectric properties of ceramics in the PMN-PZT system are investigated. The ceramics with a formula xPb(Mg1/3Nb2/3)O3-(1-x)Pb(Zr0.52Ti0.48)O3 or xPMN-(1-x)PZT when x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0 are prepared by a conventional mixed-oxide method. The ferroelectric properties under the uniaxial compressive pre-stress of the PMN-PZT ceramics are observed at the stress levels up to 13 MPa using a compressometer in conjunction with a modified Sawyer–Tower circuit. It is found that with increasing compressive pre-stress levels the area of the ferroelectric hysteresis (P–E) loops, the saturation polarization (Psat), the remanent polarization (Pr), and the coercive field (Ec) decrease. These results are interpreted through the non-180° ferroelastic domain-switching processes. Finally, the calculated differential permittivity for all the xPMN-(1-x)PZT ceramics, except for 0.5 PMN-0.5 PZT, decreases with increasing applied stress.

Crystal Plane Dependence of Giant Piezoelectricity in Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 Single Crystals

Pb[(Zn 1/3 Nb 2/3 ) 0.91 Ti 0.09 ]O 3 single crystals with various crystal planes were evaluated regarding electromechanical coupling factor of k 31 mode and piezoelectric d 31 constant. Although these values depended on their crystal planes, the giant k 31 and d 31 were obtained in the case of the (100) crystal plane poled along [001] of the original cubic direction. The dielectric constant at room temperature increased with the time in the crystal of (110) plane, while the dielectric constants of the crystals with (100) and (111) planes were unchanged. The crystal plane dependence of ferroelectric properties and their aging characteristics could be explained by the relationships between the directions of the polarization axes and poling field. The bipolar pulse field dependence of k 31 and d 31 were also investigated in comparison with the DC poling field dependence. The giant k 31 and d 31 were obtained in the crystal of (100) plane by the bipolar pulse poling as well as by the DC poling.

From single crystals to ceramics on Pb[(Zn 1/3Nb 2/3) 0.91Ti 0.09]O 3 composition

Recently, we found a giant electromechanical coupling factor of k 31 mode over 80% and a piezoelectric d 31 constant nearly −1700 pC/N in (1 0 0) plane Pb[(Zn 1/3Nb 2/3) 0.91Ti 0.09]O 3 (PZNT91/09) relaxor single crystals in addition to the large k 33 mode of over 92%. The origin of the giant k 31 and d 31 was due to realize the single-domain structure in the direction perpendicular to the poling field as well as in the direction parallel to the poling field. Through our studies, the poling field ( E) dependence of ferroelectric properties and their domain structures was investigated. The single-domain structure was achieved at E = 1000–1500 V/mm with decreasing the frequency constant (fc 31: half of the bulk wave velocity on k 31 mode) and the giant k 31 was obtained at the minimum fc 31 of 522 Hz m. While the single-domain was divided into two domains over E = 1500 V/mm, the k 31 decreased and fc 31 increased. As the formation of a domain wall, which corresponds to a grain boundary in ceramics, caused the increase of the fc 31 (Young's modulus), the material became mechanically hard. Moreover, we evaluated PZNT91/09 single crystals with (1 0 0), (1 1 0) and (1 1 1) planes for their aging properties. Large aging occurred in the crystals with (1 1 0) plane, on the other hand, little aging in (1 0 0) and (1 1 1) planes. Namely, the ferroelectric and their aging properties depended on the crystal planes. Since ceramics are composed of the small-size single crystals, our results were very helpful to understand the roles of grain boundaries, grain size, domain size and crystal planes in piezoelectric materials. Furthermore, from the relationships between coupling factors of k 31, k 33 and Young's modulus on various kinds of single crystals and ceramics, future research on the piezoelectric materials including lead free materials was proposed.

Compositional Dependence of Ferroelectric Properties for (Y,Yb)MnO3 Thin Films Prepared by Chemical Solution Deposition

The (Y,Yb)MnO3 thin films were prepared using alkoxy-derived precursor solutions. The hexagonal phase crystallized in Ar atmosphere and the films had high crystallinity and high degrees of c-axis orientation. The substitution of Y by Yb in YMnO3 lowered the crystallization temperature. The Y0.5Yb0.5MnO3 and YbMnO3 films crystallized at 700°C had c-axis orientation and showed the saturated P-E hysteresis loop. The remanent polarization and coercive field were 1.7 μC/cm2 and 100 kV/cm for Y0.5Yb0.5MnO3 film, and 2.1 μC/cm2 and 100 kV/cm for YbMnO3 film, respectively. The Y0.5Yb0.5MnO3 film crystallized at 700°C showed good fatigue property.