Influence of sintering temperatures on the electrical property of bismuth sodium titanate based piezoelectric ceramics

A systematic investigation of cerium and stannum doped 0.94(Bi_0.5Na_0.5)TiO₃−0.06BaTiO₃ (Sn&Ce-BNT6BT) based lead-free piezoelectric ceramics is undertaken to understand the influence of sintering temperature on electrical properties. The X-ray diffraction patterns showed that all of the Sn&Ce-BNT6BT ceramics exhibited a single perovskite structure with the co-existence of the rhombohedral and tetragonal phase. The smaller grain size of Sn&Ce-BNT6BT ceramics was obtained at lower sintering temperature, and more cubical grains of Sn&Ce-BNT6BT ceramics were obtained at higher sintering temperature. The temperature dependence of dielectric permittivity of the compositions exhibited strong dispersion with the increasing temperature, and the dielectric loss tangent increased dramatically while the temperature over 225^∘C. The depolarization temperature T _d of Sn&Ce-BNT6BT ceramics sintered at 1160^∘C was 92.6^∘C. The remnant polarizations P _r for Sn&Ce-BNT6BT ceramics sintered at 1120 and 1200^∘C were found to be 28.8 and 33.4 μC/cm² at room temperature, respectively.     

Ferroelectric and dielectric properties of sol-gel and excimer-laser-deposited lead zirconate titanate and barium titanate films

Abstract

Switched remanent polarization was measured as a function of accumulated switching cycles for a variety of ferroelectric films using sinusoidally driven hysteresis loops. Switched remanent polarization and dielectric constant and loss were also obtained as a function of the cycling frequency. PZT films with niobium additives appeared to lose switched remanent polarization with accumulated cycles at a lesser rate than films without niobium. The switched remanent polarization was found to decrease with increasing frequency, which we attribute to the effect of grain size. Also, a decrease of dielectric constant with increasing frequency and an increase of dielectric constant with increased applied voltage are attributed to the effects of domain wall motion contributions to dielectric constant.     

Electrical and dielectric properties of barium titanate – polydimethylsiloxane nanocomposite with 0-3 connectivity modified with carbon nanotube (CNT)

Abstract

This study explored the preparation and electrical properties of 0–3 barium titanate/polydimethylsiloxane nanocomposites by dispersing barium titanate nanoparticles (BaTiO₃; BT) into the polydimethylsiloxane (PDMS) matrix phase. The effect of barium titanate nanoparticles on electrical properties has been investigated systematically, and the relative permittivity of nanocomposites was found to increase significantly with increasing barium titanate content. Different theoretical models were used to predict the dielectric constant of these composites and compare their experimental value with the theoretical value in order to find an appropriate equation. The result indicated that the dielectric properties of composites are influenced not only by relative permittivity of the components but also dependence on interactions between ceramics and polymers. Furthermore, the preparation and dielectric properties of BT/PDMS nanocomposites modified with carbon nanotube (CNT) were also studied. The dielectric results demonstrate that adding CNT can enhance the relative permittivity of the BT/PDMS composite via improvement of dispersion and distribution of the BT nanoparticles in the PDMS matrix phase. Moreover, the electrical outputs from the BT/PDMS/CNT nanocomposites generator were measured under periodic knocking. The nanocomposites innovatively expand the feasibility of self-powered energy systems for smart sensor and energy harvesting applications.     

Temperature dependence of the dielectric dispersion and ferroelectric properties of neodymium doped bismuth titanate ceramics

Nd-doped bismuth titanate Bi_{4 − x} Nd _x Ti₃O₁₂ ceramics (x = 0–1.0) were prepared by the solid state reaction method. The temperature dependence of the dielectric dispersion and ferroelectric properties were investigated. With the increase of the Nd substitution for Bi ion, the Curie temperature decreased and the corresponding dielectric constant peak broadened. In addition, the strong low-frequency dielectric dispersions were exhibited. The Nd doping decreases the temperature dependence of the ac conductivity and increases the temperature dependence of the remanent polarization, which is caused by the induced polarization by defects, such as bismuth and oxygen vacancies.     

Pyroelectric and dielectric properties of lead lanthanum zirconate titanate (Pb0.92La0.08)(Zr0.65Ti0.35)O3-P(VDF/TFE)(0.98/0.02) nanocomposites

PLZT-P(VDF/TFE) 0–3 composites with nanosized lead lanthanum zirconate titanate (Pb_0.92La_0.08)(Zr_0.65Ti_0.35)O₃ (PLZT 8/65/35) ceramic powders of volume fraction Φ up to 0.2 were fabricated using PLZT powders imbedded in a copolymer P(VDF/TFE)(0.98/0.02) matrix. The PLZT nanopowders were prepared by the sol-gel technique. The PLZT-P(VDF/TFE) composite samples were prepared from ceramic and polymer powders by the hot-pressing method. Dielectric response was studied in the frequency range from 100 Hz to 1 MHz and at temperatures from 100 to 450 K. The pyroelectric properties were studied by dynamic method with modulation frequency from 1 to 100 Hz. The dielectric response of the ceramics-polymer composite was found to be a combination of the responses of the pure polymer and the ceramics: (1) the addition of the PLZT ceramics increases the value of the dielectric permittivity ɛ′, (2) the composite shows the maximum of the permittivity coming from the PLZT ceramics, (3) the temperature dependences of the dielectric loss tgδ are characterized by the maximum attributed to the α-relaxation (glass transition) in the pure polymer. The pyroelectric coefficient of the composite increases from ∼20 μC/m²K in pure P(VDF/TFE) to ∼140 μC/m²K in the composites of Φ = 0.15.     

Fabrication and electrical properties of PC-PNZT-PVDF-GO composites

The objectives of this research are to fabricate and investigate new smart composites for the sensing and actuation applications in civil engineering. The fabrication and properties of cement-based piezoelectric ceramic composites are emphasized. However, cement-based piezoelectric composites are still difficult to obtain great electrical properties due to the evidence of some pores in the composites. Therefore, a novel approach to effectively improve their polarization of piezoelectric ceramic is to add a semiconductor (graphene oxide) and an insulator (polyvinylidene fluoride) phases between piezoelectric particles by the introduction of a small volume fraction of a third phase. Microstructure of the new composites was investigated using Scanning electron microscope (SEM). Dielectric permittivity and ferroelectric properties were then investigated.     

分散剂对钛酸钡介电性能的影响

通过水煮损耗测试、温度特性、电导率和化学分析、瓷片表面显微结构等测试手段,研究了在固相反应制备钛酸钡的工艺中,向BaCO3粉体和TiO2粉体的混合球磨的浆料中加入聚乙烯醇作为分散剂对合成的钛酸钡粉体均匀性的影响。研究结果表明,碱性聚乙烯醇改善合成BaTiO3粉体均匀性的效果最好,介电常数峰值提高了2313、游离BaO含量降低了93.33％。     

Phase transformation and microwave dielectric properties of BiPO4 ceramics

Monazite-type compounds, BiPO₄ polymorphs were prepared by the solid-state reaction method. The phase transformation and microwave dielectric properties of sintered ceramics were investigated using the X-ray powder diffraction (XRD) and a network analyzer, respectively. The low-temperature phase of BiPO₄ has monoclinic structure, and was transformed into the high-temperature phase with a slight distortion of monoclinic when it is heated above 600^∘C. The effect of the transformation on the microwave dielectric properties was examined. It was found that the dielectric properties of each phase were significantly different. In particular, the high-temperature phase sintered at 950^∘C has good microwave dielectric properties; the relative dielectric constant (ε _r ) = 22, the quality factor (Q× f) = 32,500 GHz and the temperature coefficient of resonant frequency (τ _f ) = − 79 ppm/ ^∘C.     

Electrical properties of bismuth germanate (Bi2GeO5) ferroelectric glass-ceramics prepared by two different methods

Abstract

Ferroelectric Bi₂GeO₅ glass-ceramics were fabricated using conventional and incorporation method. Glasses have been prepared from BiO_1.5-GeO₂-BO_1.5 ternary glass system by focusing on the region of 59?mol%BiO_1.5: 23?mol%GeO₂: 18?mol%BO_1.5. The resulting glass was analyzed by using differential thermal analysis (DTA) for determining the crystallization temperature (T_p). Then, the prepared glass pieces were heat treated at T_p. Effects of different fabrication methods on structure and electrical of the glass-ceramics were investigated. X-ray diffraction result of all glass-ceramics suggested that the main peak of glass-ceramics matched the orthorhombic structure of the pure Bi₂GeO₅ phase. Microstructures of the prepared glass-ceramics have been found to change from rod-like crystallites to bulk crystallites on modifying the fabrication method. The Bi₂GeO₅ glass-ceramics prepared by incorporation method presented higher dielectric constant than those of the Bi₂GeO₅ glass-ceramics prepared by conventional method. Moreover, the Bi₂GeO₅ glass-ceramic prepared by incorporation method possesses a large value of P_max (0.94 µC/cm²) comparing to that of the glass-ceramics prepared by conventional method (P_max = 0.73 µC/cm²). Thus, this study suggests that the incorporation method can effectively modify the microstructure of Bi₂GeO₅ glass-ceramics, resulting in the improvement of dielectric and ferroelectric properties.     

Niobium doping effects and ferroelectric relaxor behavior of bismuth lantanium titanate

Ferroelectrics Bi_3.25La_0.75(Ti_3−x Nb_x)O₁₂ (BLTN, x = 0∼ 0.1) solid solution systems were prepared, and Nb doping effects and relaxor behaviors were investigated. The BLTN single phases were confirmed by XRD. The phase transition temperature decreased as the Nb content increased, and the corresponding dielectric constant maximum broadened. The temperature T _m of the dielectric maximum depended on frequency and increased, which indicate that the relaxor behavior was caused by Nb substitution. The substitution of Nb for Ti ions affected the degree of disorder and modified the dielectric properties from those of normal ferroelectrics to relaxor ferroelectrics.     

Giant dielectric constants in K0.8M0.4Ti1.6O4 (M = Ni,Zn) lepidocrocite-type layered titanate ceramics

Abstract

We reported herein the temperature-dependent dielectric properties of K_0.8M_0.4Ti_1.6O₄ (M?=?Ni, Zn) lepidocrocite titanate ceramics at the frequency f of 10³, 10⁴ and 10⁵ Hz. This titanate is an example of layered alkali titanium oxides possessing two-dimensional (2D) sheets of edge-shared TiO₆ octahedra, in contrast to other widely studied materials with mostly corner-shared TiO₆ motifs. The giant dielectric constants ε′ ～10⁴ and the dielectric losses tan δ ～ 0.5–2 were obtained upon heating from RT to 250?°C. These values in our water-free ceramics are comparable to those previously reported in lepidocrocite titanate and related structures containing up to 15%wt water. The results were explained considering (i) Maxwell-Wagner polarization of interlayer species, and (ii) the possible formation of internal barrier layer capacitors (IBLCs) via the oxidized surfaces.     

Bottom electrode etching effect on the electrical properties of lead strontium titanate thin film

(Pb_0.4Sr_0.6)TiO₃ thin films were prepared by a modified sol-gel method on Pt/Ti/SiO₂/Si substrates, where lower figure of merit of about 16% was observed in spite of higher tunability above 58%. The electrode surface was etched with different CF₄ and Ar gas ratios to modify the surface roughness. The electrical properties of PST thin films were investigated as a function of etching condition and film thickness. With changing CF₄/(Ar+CF₄) gas composition, the dielectric loss and the figure of merit were apparently affected which can be explained in terms of the surface roughness of Pt bottom electrode. When the Pt electrode surface was etched by using CF₄/(Ar+CF₄) = 20% gas mixture, the improvement above 25–27% in dielectric loss and figure of merit was observed, according to the decreased rms value of Pt surface of ∼30%, from 1.8 to 1.2 nm. The etching effect was found to be dominant for the dielectric loss and the thinner films.     

Preparation and properties of sputtered lead titanate thin films on MgO single crystals and mgo buffer layers

Abstract

By means of planar multitarget sputtering (001) oriented PbTiO₃ films were deposited onto highly preferred (100) oriented platinum electrodes on (100) MgO single crystal substrates. Single phase perovskite type films with a degree of (001) orientation between 60% and 70% have been sputtered at substrate temperatures as low as about 470°C. The as grown films exhibit a dielectric constant in the range of 120 to 140 and a pyroelectric coefficient of about 20 nCcm^?2K^?1 at room temperature. The dielectric loss is about 0.01 at frequencies from 1 to 10 kHz. (100) GaAs substrates with an evaporated, highly oriented (100) MgO buffer layer were also used as substrates. However, on these substrates the platinum bottom electrode did not grow highly oriented though the same deposition parameters for Pt deposition as in the case of the single crystalline MgO substrate were used. That's why PbTiO₃ was produced with a lower (001) preferred orientation. Therefore, the dielectric constant is higher (170–190) and the pyroelectric coefficient is lower (12 nCcm^?2K^?1).     

Effect of raw material on properties of Ba0.55Sr0.45TiO3/MgO composites

The effect of raw material on properties of Ba_0.55Sr_0.45TiO₃/MgO composites was studied. The Ba_0.55Sr_0.45TiO₃ was prepared by BaCO₃, SrCO₃, TiO₂ and BaTiO₃, SrTiO₃. The MgO was prepared by heavy magnesium oxide, light magnesium oxide and basic magnesium carbonate, respectively. The crystalline phases of all ceramics were the same. Whereas, the grain size, lattice parameters, microwave dielectric properties and tunability of the samples were different. Overall, the Ba_0.55Sr_0.45TiO₃/MgO composites, in which BST were prepared from BaCO₃, SrCO₃ and TiO₂, and MgO was prepared by heavy magnesium oxide, exhibited excellent properties of ?_r = 141.55, Q × f = 905 GHz and n_r = 7.16% (E = 3 kV/mm).     

Sintering and dielectric properties of Al2O3 ceramics doped by TiO2 and CuO

The effects of CuO and TiO₂ additives on the microstructure and microwave dielectric properties of Al₂O₃ ceramics were investigated. Al₂O₃ ceramics with CuO and TiO₂ additions can be well sintered to achieve 93∼98% theoretical densities below 1,360 °C due to Ti₄Cu₂O liquid phase sintering effect. The Qf values decreased with increasing CuO and TiO₂ content, due to the formation of the second phase Ti₄Cu₂O. However, the varying behaviors of the dielectric constant (ɛ _r ) and temperature coefficients (τ _f ) were associated with phase constitutions, as a result of the change of CuO and TiO₂content. The τ _f can be shifted close to 0 ppm/°C by controlling the content of CuO and TiO₂. The specimens with 0.5 wt.% CuO and 7 wt.% TiO₂ sintered at 1,360 °C for 4 h showed ɛ _r of 11.8, Qf value of 30,000 GHz, and τ _f of −7 ppm/°C.     

Morphotropic phase boundary and electrical properties of lead-free bismuth sodium lanthanum titanate—barium titanate ceramics

The important properties of lead-free piezoelectric ceramics have been investigated from Bismuth Sodium Lanthanum Titanate and Barium Titanate system: (1 − y)(Bi_0.5Na_0.5)_{(1 − 1.5x)}La _x TiO₃(BNLT)—yBaTiO₃(BT) where x = 0.017 and y = 0 − 0.2, respectively. The morphotropic phase boundary (MPB) was found to be around y = 0.1 by the x-ray diffraction and dielectric measurement at various amount of BT. The temperature dependence of dielectric constant (ε _r ) at various value of y showed the diffuse phase transition exhibiting the relaxor type ferroelectrics. The degree of diffuseness increased at a high doping content of about y = 0.15 where the second phase transition (T₂) of the ferroelectric to antiferroelectric phase disappeared. Moreover, this sample had the maximum piezoelectric coefficient (d ₃₃) of about 112 pC/N with relatively low dielectric constant. The optimum sintering temperatures and the microstructures of the dense BNLT-BT ceramics were also examined.     

Dielectric properties of nanocrystalline barium zirconate titanate synthesized by glycine-nitrate autocombustion

Abstract

Dielectric properties of nanocrystalline barium zirconate titanate (Ba(Zr_xTi_1-x)O₃; BZT for x?=?0.1 and 0.3) synthesized by glycine-nitrate autocombustion method were investigated in this study. The phase formation examined by TGA-DTA, XRD, FT-IR and Raman spectroscopy confirmed that high purity single-phase BZT with perovskite structure was obtained by using glycine-to-nitrate molar ratio of 2.2:4 and calcining in air at 1100?°C for 4?h. TEM analysis showed that BZT had agglomerate particles consisted of primary spherical nanocrystals with the size of 8-11?nm. The diffuse phase transition behavior of BZT ceramics increased with increasing Zr concentration and for x?=?0.3, the Curie temperature; T_c, shifted to below room temperature. The BZT ceramics for x?=?0.1 had relatively high dielectric constant (ε), 13007, low T_c, 76?°C and comparable dielectric loss (tan δ) at T_c, 0.012 which caused by the high degree of Zr diffuseness into the perovskite structure. These results suggest that glycine-nitrate autocombustion is the effective method for preparing high quality BZT ceramics.     

Electrodynamic properties of single-crystal and thin-film strontium titanate

Abstract

We present a comparative study of broadband electrodynamic properties of coplanar waveguides made from nonlinear dielectric single-crystal and thin-film SrTiO₃ (STO) with high-temperature superconducting thin-film YBa₂Cu₃O_7-δ electrodes. The waveguides that use single-crystal STO exhibit a monotonic increase in refractive index, dielectric nonlinearity, and dissipation with decreasing temperature (from 80 K to 20 K), whereas those based on thin-film STO show similar but weaker effects with increasing temperature. Under dc bias, both types of waveguides show reduced refractive index, but dissipation increases in the case of single-crystal STO, while it decreases in the case of STO thin-films.     

Microwave dielectric properties of temperature stable Ca5A2Ti1−x Hf x O12 (A = Nb, Ta) ceramics

Ca₅A₂Ti_1−xHf_xO₁₂ (A = Nb, Ta) ceramics have been prepared as single-phase materials by conventional solid-state ceramic route. Their structure and microstructure were studied by X-ray diffraction and scanning electron microscopic methods and dielectric properties were characterised in the 4–6 GHz microwave frequency range. We observed an increase in cell volume and theoretical density with compositional variations. In Ca₅Nb₂Ti_1−xHf_xO₁₂ ceramics the dielectric constant varied from 48 to 22 and quality factor from 26000 to 16000 GHz whereas in Ca₅Ta₂Ti_1−xHf_xO₁₂ the variation in dielectric constant was from 38 to 17 and quality factor from 33000 to 18000 GHz with increase in x. In both the ceramic systems the temperature coefficient of resonant frequency shifted from positive to negative values with Hf ⁴⁺ substitution for Ti⁴⁺.