Investigation of dielectric and relaxor ferroelectric properties in Ba(Zr x Ti1−x )O3 ceramics

Barium zirconate titanate Ba(Zr _x Ti_1?x )O₃ (BZT x?=?0.1, 0.15, 0.2, 0.25) ceramics doped with Nb₂O₅ have been prepared by a traditional solid phase reaction. The temperature dependence of dielectric permittivity has been investigated. The results show that the phase transition temperature T _c is depressed and the diffuse phase transition behavior is enhanced with increasing Zr content. The Cole–Cole plot has been discussed and the cause of the deviation has been analyzed. The temperature dependence of inverse dielectric constants was investigated. A modified Curie–Weiss law can be used to describe the diffuseness of a phase transition, and diffusion factor increases with the Zr content.     

Ferroelectric Bi4Ti3O12 and Bi4−x La x Ti3O12 ceramics prepared by a new sol-gel route

Ceramics of bismuth titanate, Bi₄Ti₃O₁₂ (BIT) and the La-doped series, Bi_4?x La _x Ti₃O₁₂ (xBLT) with x?=?0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, and 0.75, have been synthesized by a new sol-gel process based on ethylene glycol. La-doping is found to reduce the temperature of the formation of pure Bi-layer-structured phase from 600 °C in BIT and low La-doped xBLT (x?=?0.1–0.3) to 500 °C in high La-doped xBLT (x?=?0.4–0.75). Increasing the La-content in the xBLT ceramics decreases the contribution of the space charge polarization to the apparent dielectric permittivity. The ceramics of xBLT prepared by this sol-gel route exhibit improved dielectric properties, with a higher room temperature dielectric constant and lower losses up to high temperatures.     

Piezoelectric properties of the high temperature MPB xPbTiO3 - (1−x)[BiScO3 + Bi(Ni1/2Ti1/2)O3] composition

The ternary perovskite xPbTiO₃ - (1?x)[BiScO₃ + Bi(Ni_1/2Ti_1/2)O₃] (PT-BS-BNiT), where x?=?0.54 is the morphotropic phase boundary composition, was studied for high temperature ferroelectric applications. Polycrystalline ceramics were prepared using the standard solid-state methods. The stoichiometric ceramic was found to have room temperature dielectric permittivity and loss values at 1 kHz of 1490 and 0.049 respectively. Piezoelectric properties, of the stoichiometric composition, measured included: P_r?=?31.0 μC/cm², E_c?=?25.0 kV/cm, d₃₃?=?340 pC/N, d₃₃ ^*?=?896 pm/V, and a bipolar electromechanical strain of 0.25 %. From these data, the Curie temperature was T_C?=?370 °C and the depoling temperature was T_D?=?325 °C. Processing ceramics with excess bismuth improved the low field piezoelectric coefficients with a maximum of d33?=?445 pC/N, while increasing the lead content increased the transition temperatures. The depoling and Curie temperatures of all compositions were measured to be between 275 and 400 °C.     

Structural and Electrical Properties of Ba(ZrxTi1-x)O3 Films Prepared by RF-magnetron Sputtering Using Metal Targets

Ba(Zr_xTi_1-x)O₃ (BZT) thin films with different Zr contents were deposited on (100)MgO and (100)Pt/(100)MgO substrates by RF-magnetron sputtering using metal targets. The BZT thin films had a single perovskite phase with only (001)/(100) orientation. In all cases, the ratio of Ba/Ti was stoichiometry and BZT films possess a dense microstructure. The grain size was decreased and BZT thin films showed ferroelectric-to-paraelectric properties with increasing Zr content. At room temperature, the tunability of nearly 30% was achieved at 1 MHz; meanwhile, a relatively low dielectric loss was obtained. These results indicated that we succeeded in depositing high-quality and potential tunable ferroelectrics.     

Effect of Mg doping on dielectric properties of sol-gel derived (Pb0.7Sr0.3)Mg x Ti1–x O3–x thin film

(Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x (x?=?0?～?0.3) thin films were successfully prepared on ITO/glass substrate by sol-gel technique. The crystalline phase structures were measured through X-ray diffraction (XRD). The dielectric properties were measured by a precision impedance analyzer. Results show that the perovskite phase was stable in (Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x thin film. Its lattice constant was found to decrease with the increase of x when x?<?0.1 and increase when x?>?0.1.The crystalline phase formation and the dielectric properties of the (Pb_0.7Sr_0.3)Mg _x Ti_1–x O_3–x thin film depend on Mg doping content. The phase formation ability was decreased below x?=?0.1 and then increased above x?=?0.1 with the increase in x. The dielectric constant of the thin film is correspondingly changed. The tunabilities of about 35%?～?63% were obtained at 10 kHz. The highest tunability and the lowest dielectric loss of the thin films appeared at x?=?0.2. The FOM of the thin film with Mg doping of x?=?0.2 is about three times higher than that of x?=?0.1 under applied frequency of 10 kHz.     

Structure,Ferroelectric, Dielectric and Energy Storage Studies of Ba0.70Ca0.30TiO3, Ba(Zr0.20Ti0.80)O3 Ceramic Capacitors

Ba_0.70Ca_0.30TiO₃-(BCT),Ba(Zr_0.2Ti_0.8)O₃-(BZT) ceramics were fabricated by conventional mixed oxide route to develop inorganic dielectric materials suitable for use as an insulator with high dielectric constant and low energy loss for capacitor applications. The structural phase transition, ferroelectric, dielectric and energy storage properties of BCT, BZT ceramic capacitors were investigated. Room temperature X-ray diffraction (XRD) patterns revealed prominent peaks corresponding to tetragonal perovskite crystal structure for both BCT, BZT solid solutions. Slim ferroelectric hysteresis (P-E) loops were observed for BCT, BZT solid solutions. Temperature dependent dielectric property measurements of BCT, BZT solid solutions have shown a high dielectric constant and low dielectric loss. Room temperature (300K) breakdown field strength and energy densities were obtained from the integral area of P-E loops. For the BCT ceramics, the largest recoverable energy (unreleased energy) density is 1.41 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. For the BZT ceramics, the largest recoverable energy (unreleased energy) density is 0.71 J/cm³ with dielectric breakdown strength as high as 150 kV/cm. Bulk BCT, BZT ceramics have shown interesting energy densities; these might be the strong candidate materials for capacitor applications.     

Effect of Zr/Ti ratio on piezoelectric and dielectric properties of PNW–PMS–PZT ceramics

(Pb_0.95Sr_0.05)[(Ni_1/2W_1/2)_0.02(Mn_1/3Sb_2/3)0.06(Zr_XTi_Y)_0.92]O₃ piezoelectric ceramics (abbreviated as PNW–PMS–PZT) with 1%mol excess PbO, 0.25 wt% CeO₂ and 0.2 wt% MnO₂ were prepared by traditional ceramics process. The phase structure of ceramics sintered at 1150°C were analyzed. Results show that the pure perovskite phase was in all ceramics specimens, the phase structure of PNW–PMS–PZT piezoelectric ceramics was transformed from tetragonal to rhombohedral, with Zr/Ti ratio increased in system; Effect of Zr/Ti ratio on piezoelectric and dielectric properties was investigated. Results show that ? _r , tanδ, k _p and d ₃₃ increased with an increase of Zr/Ti ratio and reached the maximum values at Zr/Ti ratio of 50/50, then decreased with further increase of Zr/Ti ratio, whereas the variation of Q _m with an increase of Zr/Ti ratio showed the opposite trend, T _c showed a tendency to decrease with an increase of Zr/Ti ratio. The piezoelectric ceramics with Zr/Ti ratio of 50/50 was applied in high-power multilayer piezoelectric transformer, and properties parameter were ? _r ?=?2100, tanδ?=?0.006, k _p ?=?0.613, Q _m ?=?1300, d ₃₃ ?=?380pC/N, T _c ?=?205 °C.     

Preparation and characterization of high T c (1−x) BiScO3−xPbTiO3 ceramics from high energy ball milling process

(1-x)BiScO₃?xPbTiO₃ powders were synthesized from a mixture of the oxides Bi₂O₃, Sc₂O₃, PbO and TiO₂ using a Fritsch P4? vario-planetary ball milling systems. The pure perovskite structure of BS-PT powder can well be obtained and the crystallite size of the powders was greatly reduced to 18–25 nm after milling 4 h. The rhombohedral–tetragonal phase boundary was observed for the ceramics sintered at 1,000–1,100 °C when x was around 0.64 and 3–7 μm grain size was obtained, which is smaller than traditional method. High Curie temperature (T _c) and high dielectric constant can be obtained at the morphotropic phase boundary (MPB). As PbTiO₃ contents increased from 60 to 68 mol%, the Curie temperature T _c shifted toward higher temperature and the maximum dielectric constant increased. The experimental results demonstrate that the high-energy ball milling process is a promising method to prepare BS-PT materials.     

Dielectric,ferroelectric, and piezoelectric properties of lead-free Ba0.95Ca0.05Ti1-xZrxO3 ceramics

Abstract

Ba_0.95Ca_0.05Ti_1-xZr_xO₃ (BCTZO) ceramics were prepared by a solid state reaction method. The samples were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and X-ray absorption near edge structure (XANES). The ceramics exhibit a pure perovskite structure. The average grain size gradually decreases with increasing Zr concentration. XANES results indicate that the intensities of pre-edge peaks dropped with increasing Zr concentration. The BCTZO ceramic of x?=?0.05 has the optimum electrical properties with the maximum dielectric constant (ε'_m), remanent polarization (2P_r), coercive electric field (2E_c) and piezoelectric charge constant (d₃₃) of 7,244, 12.54 (μC/cm²), 5.29 (kV/cm) and 288 (pC/N), respectively.     

High piezoelectric activity in lead-free BaTiO3-BaZrO3-CaTiO3 ceramics with near polymorphic phase boundary

Abstract

Lead-free 0.88BaTiO₃–(0.12-x)BaZrO₃–xCaTiO₃ (BT-BZ-xCT) ceramics were fabricated via solid state reaction. The effect of CaTiO₃ content on crystal structure, phase transition, and electrical properties was investigated systematically. The crystal structure and phase transition of ceramics were characterized by X-ray diffraction (XRD), Raman spectra and dielectric measurement. Results show that ceramic in the composition, x?=?0.02, exhibits a rhombohedral structure. Ceramics with increasing CT content transformed from a rhombohedral to orthorhombic structure in the composition, x?=?0.04, and eventually became a tetragonal structure at the composition, x?≥?0.08. The polymorphic phase boundary (PPB) was observed at the composition, x?=?0.06, with coexistence of orthorhombic and tetragonal phases showing at almost room temperature. This PPB composition exhibited a high piezoelectric response (d₃₃*) of 1,150?pm/V at 10?kV/cm as an electric field was applied. These results indicate that the materials studied have potential as candidates for lead-free piezoelectric ceramics.     

Relaxor behavior of piezoelectric Pb(Yb1/2Nb1/2)O3-PbTiO3 ceramics sintered at low temperature

A (100-x)Pb(Yb_1/2Nb_1/2)O₃-xPbTiO₃ [PYN-PTx] solid solution system with 49.0????×????51.0 was prepared using a conventional ceramics process and sintered at low temperature. When excess PbO was added into the PYN-PTx system, all samples were sintered at temperatures as low as 800°C with good dielectric and piezoelectric properties. It is suggested that a liquid phase with excess PbO was formed during the sintering and improved the densification of PYN-PTx ceramics at low temperatures. For the PYN-PTx binary system, it was found that the temperature dependence of the relative permittivity follows a Curie?CWeiss Law above the deviation temperature (T_D) at high temperatures. Good piezoelectric properties of d ₃₃ ?=?510 pC/N, ?? _r ?=?2800 at RT, k _p?=?0.57, and k _t?=?0.42 with T_c?=?373°C were obtained for PYN-PT49.5 ceramics sintered at 800°C for 8 h.     

The variation of Curie temperature and dielectric relaxor behaviour in the nominal (1-x)BaTiO3-xBiAlO3 system

BiAlO₃ is a perovskite ferroelectric with a high Curie temperature above 520°C. However, it is difficult to prepare pure perovskite phase by the conventional method. In this experiment, BaTiO₃ has been selected as host to incorporate BiAlO₃, and the nominal binary system of (1-x)BaTiO₃-xBiAlO₃ has been investigated with regard to its Curie temperature (T _c) and dielectric relax behaviors. It was found that the pure perovskite phase can be retained below x?=?0.08. However, the value of T _c in the system doesn’t follow the normal Vegard’s law, on the contrary, shows the decreasing trend with the increase of x. According to the compared experiments about Bi³⁺ and Al³⁺ doping in BaTiO₃, it can be safely concluded that the combined substitution of Bi³⁺ and Al³⁺ played the dominant role to decrease the T _c and increase the relaxor behavior in (1-x)BaTiO₃-xBiAlO₃ system.     

Excellent dielectric constants observed in heterogeneous conduction Ba(Zr<Subscript>0.25</Subscript>Ti<Subscript>0.75</Subscript>)O<Subscript>3</Subscript> ceramics doped with Sr(Fe<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>)O<Subscript>3</Subscript>

The (1-x)Ba(Zr_0.25Ti_0.75)O₃-xSr(Fe_0.5Nb_0.5)O₃ or (1-x)BZT-xSFN ceramics have been fabricated via a solid-state reaction technique. All ceramics exhibit a pure phase perovskite with cubic symmetry. The addition of a small amount of SFN (x?=?0.1) produces an obvious change in dielectric behavior. Very high dielectric constants (ε_r?>?164,000 at 1 kHz and temperature?>?150°C) are observed and the value is obviously higher than dielectric constants for Ba(Zr_0.25Ti_0.75)O₃ and Sr(Fe_0.5Nb_0.5)O₃ ceramics. The ferroelectric measurement data suggests that the unmodified sample exhibited a ferroelectric behavior. However, a transformation from a ferroelectric to a relaxor-like behavior is noted with increasing x concentration. Impedance Spectroscopy (IS) analysis indicates that the presence of excellent dielectric constants is due to the heterogeneous conduction in the ceramics after adding SFN, which can be explained in terms of the Maxwell-Wagner polarization mechanism.     

Dielectric measurements on a novel Ba1 − x Ca x TiO3 (BCT) bulk ceramic combinatorial library

High-throughput combinatorial methods have the potential to discover new materials. They can investigate the effects of a wide range of dopants on the dielectric properties to optimize existing systems, encouraging the short innovation cycles that industry requires. We are currently part of a consortium of London Universities exploring methods of producing and measuring combinatorial libraries of microwave dielectric ceramics. The London University Search Instrument (LUSI) is a fully automated, high-throughput combinatorial robot that has the potential capability to produce combinatorial libraries consisting of large numbers of sintered bulk ceramic samples with varying composition, on alumna substrates. We have reported the manufacture and characterisation of Ba _x Sr_1???x TiO₃ libraries (x in steps of 0.1) as a proof of concept to demonstrate that the robot works and to confirm a compositional and functional change throughout the libraries, as well as proving that reliable measurements can be made on such small samples. Libraries of Ba_1???x Ca _x TiO₃ samples were made with varying compositions of x?=?0–1 in steps of 0.1, and fired to 1400 °C for 1 h, by LUSI. X-ray diffraction (XRD) data agreed with the few previous reports on this little-studied system, namely that after initially forming a solid solution with Ca addition, above x?=?0.2 a two phase system forms with values of 0.2?<?x?<?0.9, after which a single phase system again appears with values of x?=?0.9 and higher. Dielectric measurements (100 Hz–1 MHz) showed a previously reported unusual initial increase in the Curie point with substitution up to x?=?0.2, followed by a rapid decrease to below 125 K when x?>?0.4. This initial increase has been attributed to the Ca substituting in both the Ba²⁺ A sites and the Ti⁴⁺ B sites of the perovskite up to x?=?0.2, after which T _c decreases greatly as the two phase system forms. Scanning probe microscopy and piezo response force microscopy (PFM) experiments also showed evidence of an increase in piezoelectricity with small amounts of x (0.1–0.2), followed by a decrease with increasing x.     

Preparation,characterisation, and electrical properties of (K0.5Na0.5)NbO3 lead-free piezoelectric ceramics

Na_0.5?K_0.5NbO₃ (KNN) ceramics were sintered at different temperatures (970 °C, 1000 °C, 1030 °C, 1060 °C, and 1090 °C) for 3 h by a pressureless sintering method. The powders had been synthesised by sol–gel method, using citric acid as a coordination agent and ethylene glycol as an esterifying agent. The effects of temperature on the phase, microstructure, dielectric, ferroelectric, and piezoelectric properties of the as-prepared ceramics were analysed. The results revealed that all of the ceramics had a pure perovskite phase with orthorhombic symmetry. The piezoelectric constant (d ₃₃), the relative dielectric constant (ε _r), the planar electromechanical coupling coefficient (K _p), and the remnant polarization (P _r) initially increased and then decreased with increasing of temperature in such KNN ceramics. The volatilization of sodium and potassium increased with increasing sintering temperature. Over the range of temperatures studied, those ceramics sintered at 1060 °C had the following optimal properties: (ρ?=?3.97 g/cm³, d ₃₃?=?119 pC/N, ε _r?=?362.46, tan δ?=?0.05, K _p?=?0.23, P _r?=?11.97 μC/cm², E _c?=?10.35 kV/cm, and T _c?=?408 °C).     

Dielectric and pyroelectric properties of (1 − x)PST-xPZT ferroelectric ceramics

Pb(Sc_1/2Ta_1/2)O₃ (PST) ceramics were investigated greatly in the world for their unique pyroelectric, ferroelectric and dielectric properties and comprehensive applications on uncooled focal plane arrays, infrared detectors and other electronic devices. However, the PST ceramics doped with other perovskite ferroelectrics showed more excellent electrical and electronic properties. In this paper, (1???x)PST-xPZT(PSTZT) ferroelectric ceramics were prepared by conventional solid state process. The experiment results demonstrated that the PSTZT ceramics had pure perovskite phase. The temperature dependence of permittivity of PSTZT ceramics was investigated in detail, which indicated that PSTZT was not a complete diffusive phase transition ferroelectric ceramics. At room temperature, the pyroelectric coefficient of PSTZT (x?=?0.1) ceramics was about 15*10^?8C/(cm² K).     

Phase transition behavior and electrical properties of lead-free (1-x)KNLNS-xBNKZ piezoelectric ceramics

Lead-free (1-x)(K_0,48Na_0,48Li_0,04)(Nb_0,95Sb_0,05)O₃-xBi_0.5(Na_0.82K_0.18)_0.5ZrO₃ (KNLNS-xBNKZ) piezoelectric ceramics (x?=?0, 0.02, 0.04, 0.06, 0.08, and 0.1) were successfully prepared by the two-step sintering method. The effects of different BNKZ contents on the crystal structure, ferroelectric phase transition, and electrical properties of the as-prepared ceramics were systematically researched. The ceramics with a perovskite structure possessed an orthorhombic phase (space group?=?Amm2) at x?=?0, a mixed orthorhombic-tetragonal phase (Amm2?+?P4/mbm) at x?=?0.02, a mixed rhombohedral-tetragonal (R-T) phase (R3m?+?P4/mbm) at x?=?0.04–0.06, and a rhombohedral phase (R3m) at x>0.06. At x?=?0.04 (rhombohedral and tetragonal (R-T) phases coexisted), the ceramics manifested the best electrical properties with d₃₃?=?224 pC/N, k_p = 0.44, k_t = 0.47, T_C = 218^oC, and remanent polarization (P_r)?=?11.5µC/cm². The improvement of the electrical properties of KNLNS-BNKZ ceramics was achieved by controlling their phase compositions and microstructures.

     

Structural and electrical properties of SrBi2VxNb2?xO9 ferroelectric ceramics: Effect of temperature and frequency

Aurivillius type bismuth layered materials have received a lot of attention because of their application in ferroelectric non-volatile random access memories. Among bismuth layer structured ferroelectric ceramics SrBi₂Ta₂O₉ (SBT)/SrBi₂Nb₂O₉ (SBN) are of great interest for researchers because of their fatigue resistance and less distorted structure. Recently vanadium substitution in SBN/SBT has shown interesting electric and dielectric properties. In the present work, processing conditions, microstructure and electrical studies of vanadium doped SBN ferroelectric ceramics have been performed. Samples of compositions SrBi₂V _x Nb_2-x O₉, x = 0.0, 0.1, 0.3, 0.5 were prepared by solid-state reaction technique using high purity oxides / carbonates. The samples were calcined at 700 °C and sintered at 800 °C. X-ray diffractograms show that a single phase layered perovskite structure is formed in all the samples. Effect of partial substitution of pentavalent niobium ion (0.68 ?) by smaller pentavalent vanadium ion (0.59 ?) at B site on the microstructure, Curie temperature, Dielectric constant, Dielectric loss and electrical conductivity have been investigated. Dielectric properties of SBVN have been investigated from room temperature to 500 °C and frequency of 100 Hz to 1 MHz. Dielectric constant values at their respective Curie points are observed to increase with increasing vanadium concentration. Curie temperature is observed to be maximum in x = 0.1 vanadium doped sample. Strong relaxor like dielectric relaxation at the transition temperatures have been observed. With increasing vanadium concentration the dielectric loss is observed to increase significantly. It is also observed that dielectric loss increases with increase in temperature. The variation of conductivities in these samples is also reported.     

Ferroelectric switching and fatigue behavior for PZT/YBCO thin film heterostructures

Abstract

The dielectric and ferroelectric properties for Au/Pb(Zr,Ti)O₃/YBa₂Cu₃O_7?x heterostructures at low temperatures are reported. The fatigue behavior and the ferroelectric switching effect for the structures are also investigated. The PZT/YBCO thin film heterostructures were deposited on MgO(100) substrates by laser ablation. The ferroelectric and dielectric properties and optical response of the oriented PZT films with different thicknesses have been studied over the temperature range from 20 K to 300 K. The dielectric loss of the structure was found to decrease by an order of magnitude when the YBCO bottom electrode became superconducting. A very low fatigue rate of the structure has also been obtained below T _c of YBCO layer.     

Temperature dependent electrical properties of 0.95[(K0.5Na0.5)(1-x)Ag x NbO3]-0.05LiSbO3 ceramics

Lead free 0.95[(K_0.5Na_0.5)_1-x Ag _x NbO₃]-0.05LiSbO₃ (KNAN-LS) ceramics with x?=?0.02, 0.04, 0.06 and 0.08 have been synthesized by conventional solid state reaction route (CSSR). XRD analysis confirmed the presence of a mixed structure for x?=?0.06. The orthorhombic?Ctetragonal polymorphic phase transition (PPT) temperature and the Curie temperature (T_c) decreased with the increase in Ag⁺ ion content in KNAN-LS ceramics. The relationship between the PPT of the ceramics and the temperature dependence of electrical properties of KNAN-LS ceramics were discussed in detail. The KNAN-LS ceramics with x?=?0.06 showed better piezoelectric and electromechanical properties (d₃₃?=?227pC/N and k_p?=?42.5?%).