Pulsed excimer laser ablation growth and characterization of Ba(Sn0.1Ti0.9)O3 thin films

Polycrystalline thin films of Ba(Sn_0.1Ti_0.9)O₃ were deposited on Pt coated silicon substrates by pulsed excimer laser ablation technique. The room temperature dielectric constant of the Ba(Sn_0.1Ti_0.9)O₃ films was 350 at a frequency of 100 kHz. The films showed a slightly diffused phase transition in the range of 275–340 K. The polarization hysteresis behavior confirmed the ferroelectric nature of the thin films. Remanent polarization (P_r) and saturation polarization (P_s) were 1.1 and 3.2 μC/cm², respectively. The asymmetric capacitance–voltage curve for Ba(Sn_0.1Ti_0.9)O₃ was attributed to the difference in the nature of the electrodes. Dispersion in both the real (ε′_r) and imaginary (ε″_r) parts of the dielectric constant at low frequencies with increase in temperature was attributed to space charge contribution in the complex dielectric constant.     

Investigation of local structure of lead‐free relaxor Ba(Ti0.70Sn0.30)O3 by Raman spectroscopy

The local structure of Ba(Ti_0.70,Sn_0.30)O₃ (BSnT) was investigated using micro Raman spectroscopy from 80 to 500 K, which indicated three local phase sequences. The dielectric spectroscopy studies illustrated freezing of polar nano‐regions (PNR) below 95 K, merger of frequency dispersion at 220 K, and the origin of polar nano‐regions at 482 K. The temperature evolution of Raman spectra, basically integrated intensity, indicates non‐ergodic relaxor phase below 100 K, mature ergodic phase between 100 and 200 K, and the existence of ergodic polar clusters until 450 K, and above paraelectric phase. The observation of local phase sequences by Raman spectra are in agreement with dielectric spectroscopy anomalies. Copyright © 2008 John Wiley & Sons, Ltd.     

Evolution from relaxor-like dielectric to ferroelectric in Ba[(Fe0.5Nb0.5)1−xTix]O3 solid solutions

Ba[(Fe_0.5Nb_0.5)_1−xTi_x]O₃ (x=0.2,0.4,0.6,0.8,0.85,0.9 and 0.95) solid solutions were synthesized by a standard solid-state reaction technique. X-ray diffraction at room temperature and dielectric characteristics over a broad temperature and frequency range were evaluated systematically. The structure of Ba[(Fe_0.5Nb_0.5)_1−xTi_x]O₃ solid solutions changed from cubic to tetragonal with increasing x. A Debye-like dielectric relaxation following the Arrhenius law similar to that in Ba(Fe_0.5Nb_0.5)O₃ was observed at lower temperature in the composition range 0.2≤x≤0.8, while the relaxor ferroelectric, diffused ferroelectric and normal ferroelectric behavior were observed for x=0.85,0.9 and 0.95, respectively. The process of the evolution of relaxor-like dielectric to ferroelectric suggested the changing from dilute polar micro-domains to polar micro-domains, polar micro/macro-domains and then polar macro-domains in the present ceramics.     

Influence of B2O3 on electrical properties and phase transition of lead-free Ba(Ti0.9Sn0.1)O3 ceramics

The phase transition and electrical properties of Ba(Ti_0.9Sn_0.1)O₃ ceramics with B₂O₃ added were investigated to explore the effect of B₂O₃ addition on enhanced densification and dielectric constant of these ceramics. With increasing B₂O₃ content, a linear reduction of ferroelectric to paraelectric transition temperature was observed. In addition, higher B₂O₃ concentrations enhanced a ferroelectric relaxor behavior in the ceramics. Changes in this behavior were related to densification, second-phase formation and compositional variation of the ceramics.     

Temperature evolution of the local structure in relaxor ferroelectric Ba(Ti0.7Zr0.3)O3 studied using neutron total scattering analysis

We performed neutron total scattering measurements on relaxor ferroelectric Ba(Ti_0.7Zr_0.3)O₃ from T=350 to 50 K. Using reverse Monte Carlo modeling on the total scattering data in k-space as well as in real space, we show that the off-centering of Ti ion is the source of local polarization at all temperatures. In addition, we estimated that Ti displacement is toward the 〈111〉 direction with a magnitude of about ∼0.11 Å. We also present an evolution of Ti-O bond length distribution across the maximum permittivity temperature, which suggests a freezing of local polarization with decreasing temperature.     

Structural refinement,optical and ferroelectric properties of microcrystalline Ba(Zr0.05Ti0.95)O3 perovskite

For this study, a microcrystalline Ba(Zr_0.05Ti_0.95)O₃ (BZT) powder was prepared by a high energy ball milling method followed by calcination at 1100 °C for 4 h. The calcined powder was structurally characterized by X-ray diffraction and Rietveld refinement data, which showed that this material has a perovskite-type tetragonal structure with a space group of (P4mmm). The micro-Raman spectrum revealed local lattice distortions due to distorted octahedral [TiO₆] clusters. The temperature and frequency-dependent dielectric study of the BZT ceramic showed normal phase transition behavior. The ferroelectric property was studied by a P–E hysteresis loop. Optical band gap was investigated by ultraviolet–visible (UV–vis) absorption spectroscopy at room temperature. The UV–vis spectrum indicated that the BZT powder has an optical band gap of 3.15 eV.     

Relaxor behaviour in PZN-PT-BT ferroelectric ceramics

The relaxor behaviour of the (Pb_0.8Ba_0.2)[(Zn_1/3Nb_2/3)_0.7Ti_0.3]O₃ ferroelectric ceramic is presented. A strong dispersion of the maximum of the dielectric permittivity (ε′) below the transition temperature (T_m) is observed, which shift towards higher temperatures with increasing frequency. There is a strong deviation from the Curie-Weiss law. The results are fitted by using the Volger-Fulcher relationship, showing typical behaviour of a spin glass system. The hysteresis loops suggest relaxor behaviour.     

Orientation-dependent dielectric properties of Ba(Sn0.15Ti0.85)O3 thin films prepared by sol-gel method

The orientation-dependent dielectric properties of barium stannate titanate (Ba(Sn_0.15Ti_0.85)O₃, BTS) thin films grown on (1 0 0) LaAlO₃ single-crystal substrates through sol-gel process were investigated. The nonlinear dielectric properties of the BTS films were measured using an inter-digital capacitor (IDC). The results show that the in-plane dielectric properties of BTS films exhibited a strong sensitivity to orientation. The upward shift of Curie temperature (T_c) of the highly (1 0 0)-oriented BTS thin films is believed to be attributing to a tensile stress along the in-plane direction inside the film. A high tunability of 47.03% was obtained for the highly (1 0 0)-oriented BTS films, which is about three times larger than that of the BTS films with random orientation, measured at a frequency of 1 MHz and an applied electric field of 80 kV/cm. This work clearly reveals the highly promising potential of BTS films for application in tunable microwave devices.     

Electromechanical-induced antiferroelectricben ferroelectric phase transition in PbLa(Zr,Sn,Ti)O3 ceramic

Antiferroelectric—ferroelectric (AFE—FE) phase transition in ceramic Pb_0.97La_0.02(Zr_0.75Sn_0.136Ti_0.114)O₃ (PLZST) was studied by dielectric spectroscopy as functions of frequency (10²—10⁵ Hz) and pressure (0—500 MPa) under a DC electric field. The hydrostatic pressure-dependent remnant polarization and dielectric constant were measured. The results show that remnant polarization of the metastable rhombohedral ferroelectric PLZST poled ceramic decreases sharply and depoles completely at phase transition under hydrostatic pressure. The dielectric constant undergoes an abrupt jump twice during a load and unload cycle under an electric field. The two abrupt jumps correspond to two phase transitions, FE—AFE and AFE—FE.     

Ferroelectric relaxor behavior in hafnium doped barium-titanate ceramic

Temperature and frequency dependence of the real (ε′) and imaginary (ε″) parts of the dielectric permitivity of cubic Ba(Ti_0.7Hf_0.3)O₃ ceramic has been studied in the temperature range of 100 K to 350 K at the frequencies 0.1 kHz, 1 kHz, 10 kHz, 100 kHz for the first time. Diffuse phase transition and frequency dispersion is observed in the permittivity-vs-temperature plots. This has been attributed to the occurrence of relaxor ferroelectric behavior. The observed relaxor behavior has been quantitatively characterized based on phenomenological parameters. A comparison with the Zr doped BaTiO₃ has also been presented. For Hf doped samples transmission electron microscopy (TEM) characterization do show the presence of highly disordered microstructure at length scales of few tens of nano-meters.     

Effect of Sb doping on phase transition and relaxor behaviour of (Pb0.75Ba0.25)(Zr0.70Ti0.30)O3 ceramics

The effect of antimony dopant on phase transition, dielectric response and relaxor behaviour of (Pb_0.75Ba_0.25)(Zr_0.70Ti_0.30)O₃ ceramics was studied. Ceramic samples, with various Sb concentration from the range 1 to 4 at.%, were prepared by a conventional mixed oxide method. The crystal structure of the investigated ceramics was determined by an X-ray diffraction at room temperature that allowed to determine the unit cell parameters. Dielectric relaxation typical for ferroelectric relaxors was observed in the vicinity of diffuse ferroelectric–paraelectric phase transition. All parameters describing the relaxor behaviour determined from the Vogel–Fulcher relationship depend on the concentration of Sb dopant. The strong influence of antimony on grain structure and on remanent polarisation was confirmed as well.     

Electric field effects on the dielectric and acoustic anomalies of Pb[(Mg1/3Nb2/3)0.83Ti0.17]O3 single crystals studied by dielectric and Brillouin spectroscopies

The effect of the electric field on the dielectric and acoustic properties of Pb[(Mg_1/3Nb_2/3)_0.83Ti_0.17]O₃ single crystals was investigated as functions of temperature and the electric field strength. The dielectric constant and the acoustic mode behaviors exhibited typical relaxor behaviors when there was no bias field. The longitudinal acoustic mode showed splitting under a moderate electric field of 1 kV/cm applied along the [001] direction, indicating coexistence of macroscopic/mesoscopic ferroelectric states and relaxor states. Further increase in the electric field up to 2 kV/cm induced a clear ferroelectric phase transition, which became smeared out due to the proximity of the electric field to the critical point. The electric field-temperature phase diagram of Pb[(Mg_1/3Nb_2/3)_0.83Ti_0.17]O₃ was suggested based on the observed field-induced changes in the dielectric and the acoustic properties.     

Improved properties & fatigue resistant behaviour OF Ba(Zr0.15Ti0.85)O3 ferroelectric ceramics

The microstructure, dielectric and piezoelectric properties of Zr doped BaTiO₃ ceramics sintered at optimum temperature, are investigated. High energy ball milling technique is adopted to realize nano-sized powders of Ba(Zr_0.15Ti_0.85)O₃ ceramics. Increased boundary mobility of fine powders aided to obtain a relative density of >98.8% of theoretical density corresponding to ceramics under study. Internal stresses in these ceramics are found to be relieved by grain-boundary sliding. The Ba(Zr_0.15Ti_0.85)O₃ ceramics synthesized at relatively low sintering temperatures exhibit remarkable, enhanced dielectric properties viz. improved polarization, high unipolar strain values comparable to Zr doped BaTiO₃ single crystals of same composition, at relatively lower electric fields and also exhibit better fatigue tolerant properties. The underlying mechanisms responsible for superior dielectric, ferroelectric and piezoelectric properties are discussed.     

Dielectric,ferroelectric and field-induced strain response of lead-free BaZrO3-modified Bi0.5Na0.5TiO3 ceramics

Lead-free piezoelectric ceramics (1 − x)Bi_0.5Na_0.5TiO₃–xBaZrO₃ (BNT–BZ100x, with x = 0–0.10) were prepared using a conventional solid-state reaction method. The crystal structure, microstructure, dielectric, ferroelectric, and piezoelectric properties of BNT–BZ100x ceramics were studied as functions of different BZ content. X-ray diffraction patterns revealed that the BZ completely diffused in the BNT lattice in the studied composition range. An appropriate amount of BZ addition improved the dielectric, ferroelectric, and piezoelectric properties of BNT ceramics. The remanent polarization (P_r) and piezoelectric constant (d₃₃) increased from 22 μC/cm² and 60 pC/N for pure BNT to 30 μC/cm² and 112 pC/N for x = 0.040, respectively. In addition, electric field-induced strain was enhanced to its maximum value (S_max = 0.40%) with normalized strain (d*₃₃ = S_max/E_max = 500 pm/V) at an applied electric field of 8 kV/mm for x = 0.055. The enhanced strain can be attributed to the coexistence of ferroelectric and relaxor ferroelectric phases.     

Reversible and piezoelectric nonlinearity: The dielectric response in multicomponent solid solutions with different manifestations of the character of ferroelectric properties

Ceramics of a modified Ba multicomponent system of PbNb_2/3Zn_1/3O₃-PbNb_2/3Mg_1/3O₃-PbNb_2/3Ni_1/3O₃-PbTiO₃ were developed. A comprehensive study was peformed of the reversible dielectric nonlinearity and electromechanical, dielectric, and piezoelectric characteristics of the multicomponent ceramics, which have properties of relaxors, ferroelectric materials with diffused phase transitions, and classical ferroelectric material. Correlations between compounds, structures, properties, and ranges of application were established.     

Specific Features of the Structure and the Dielectric Properties of Sodium–Bismuth Titanate-Based Ceramics

The phase formation, specific features, and the dielectric properties of the ceramics of compositions from the region of morphotropic interface in the (Na_0.5Bi_0.5)TiO₃–BaTiO₃ system modified by Bi(Mg_0.5Ti_0.5)O₃ and also low-melting additions KCl, NaCl–LiF, CuO, and MnO₂ that favor the control of the stoichiometry and the properties of the ceramics have been studied. The ceramics are characterized by ferroelectric phase transitions that are observed as jumps at temperatures near 400 K and maxima at T_m ~ 600 K in the temperature dependences of the dielectric permittivity. The phase transitions at ~400 K demonstrate the relaxor behavior indicating the existence of polar domains in the nonpolar matrix. An increase in the content of Bi(Mg_0.5Ti_0.5)O₃ favor a decrease in the electrical conductivity and dielectric losses of the samples, and the relative dielectric permittivity at room temperature ε_rt is retained quite high, achieving the highest values ε_rt = 1080–1350 in the ceramics modified with KCl.     

A Raman and dielectric study of ferroelectric ceramics

Dielectric and Raman scattering experiments were performed on various ceramics with composition Ba(Ti_1-xZr_x)O₃. Such lead-free, environmental-friendly materials were shown, from dielectric measurements, to exhibit behaviours extending from conventional to relaxor ferroelectrics on increasing the zirconium concentration. The evolution of the Raman spectra was studied as a function of temperature for various compositions, and the spectroscopic signature of the corresponding phases was determined. In the relaxor state, the variation of the integrated intensity of the Raman lines with temperature showed a plateau at low temperature. This anomaly was also detected as a peak in depolarization current measurements, and attributed to ergodicity breaking which characterizes usual relaxor systems. Raman results hint at locally rhombohedral polar nanoregions resulting from the random fields associated with Zr ions. Received 25 September 1998     

Relaxor behavior of (Ba,Sr)(Zr,Ti)O3 ferroelectric ceramics

We examine the ferroelectric-relaxor behavior of (Ba_0.65Sr_0.35)(Zr_0.35Ti_0.65)O₃ (BSZT) ceramics in the temperature range from 80 to 380 K. A broad dielectric maximum, which shifts to higher temperature with increasing frequency, signifies the relaxor-type behavior of these ceramics. The value of the relaxation parameter γ∼2 estimated from the linear fit of the modified Curie-Weiss law, indicates the relaxor nature of the BSZT ceramics. The dielectric relaxation rate follows the Vogel-Fulcher relation with T_VF=107 K, E_a=0.121 eV, and ν₀=6.83×10¹⁴ Hz, further supports such relaxor nature. The slim P-E hysteresis loop and ‘butterfly’ shape dc bias field dependence of permittivity at T>T_m (T_m, the temperature of permittivity maximum) clearly signifies the occurrence of nanopolar clusters, which is the typical characteristic of ferroelectric relaxor. At 300 K and 10 kHz, the dielectric constant and loss tan δ are ∼1100 and 0.0015, respectively. The high tunability (∼25%) and figure of merit (∼130) at room temperature show that the BSZT ceramics could be a promising candidate for tunable capacitor applications.     

Effects of Zr/Ti ratio on dielectric and ferroelectric properties of 0.8Pb(ZrxTi1−x)O3–0.2Pb(Co1/3Nb2/3)O3 ceramics

The influences of Zr/Ti ratio on electrical properties of the 0.8Pb(Zr_xTi_1−x)O₃–0.2Pb(Co_1/3Nb_2/3)O₃ ceramics prepared by a mixed-oxide method (with x = 0.46, 0.48, 0.50, 0.52, and 0.54) have been investigated in order to identify the morphotropic phase boundary composition in this system. With XRD analysis, the crystal structure of dense specimens appeared to change gradually from tetragonal to rhombohedral with increasing Zr content. The dielectric properties measurements showed a maximum dielectric constant at x = 0.50, while the transition temperature decreased with increasing Zr content in the system. Moreover, all ceramics showed diffused phase transition behaviors with a minimum diffusivity at x = 0.50. In addition, the Polarization–Electric field (P–E) hysteresis loops of the ceramic systems also changed significantly with the Zr content. Interestingly, the loop squareness parameter reached maximum around x = 0.50. Other ferroelectric hysteresis parameters showed noticeable change at x = 0.50. These results clearly showed the significance of Zr/Ti ratio in controlling the electrical properties of the PZT–PCN ceramic systems.     

Effects of yttrium substitution on structural and electrical properties of barium zirconate titanate ferroelectric ceramics

In the present study, structural, dielectric and ferroelectric properties of Ba_1?3x/2Y_x Zr_0.025Ti_0.975O₃ ferroelectric ceramics have been investigated. The compound was synthesized using solid state reaction technique. The effect of yttrium substitution on structural, dielectric and ferroelectric properties was studied using X-ray diffractometer, scanning electron microscopy (SEM), LCR meter and P–E loops. Phase analysis shows the formation of secondary phase YTi₂O₆ for Y ≥ 2.5 mol% substitution. The microstructural investigation shows that Y substitution significantly reduces the grain size. An increase in Y content up to 2.5 mol% increases the Curie temperature (T_c) initially but decreases subsequently. The maximum dielectric constant at T_c has been observed for 2 mol% Y substitution and with further increase in Y content the dielectric constant decreases considerably. The solubility limit is found to be 2.5 mol% of Y and after that some of the yttrium atoms enter B-sites and leading to the formation of the secondary phase. The P–E loop studies show that there is an increase in the coercive field with increasing Y content.