TiO3 Content Research Articles

Maintaining local displacive disorders in Na0.5Bi0.5TiO3 piezoceramics by K0.5Bi0.5TiO3 substitution

A comprehensive global and local structural characterization using X-ray and neutron diffraction, and EXAFS have been performed to investigate the effect of electrical poling on the structure of (1−x)Na0.5Bi0.5TiO3–(x)K0.5Bi0.5TiO3 compositions. While the annealed samples showed definite indication of presence of local displacive disorders in all the compositions studied (0<x<0.3), this disorder persisted to some extent even after poling the samples. The tendency of electric field to reduce the local displacive disorder decreased with increasing K0.5Bi0.5TiO3 content in the samples.

Broadband Near-Infrared Photoluminescence and Strong Visible Up-Conversion Emission in BaTiO3-(Na0.5Er0.5)TiO3 Lead-Free Piezoelectric Ceramics

For checking photoluminescence properties of BaTiO3-(Na0.5Er0.5)TiO3 lead-free piezoelectric ceramics, optical diffuse reflection spectra, visible up-conversion luminescence spectra, 1.55 μm near-infrared photoluminescence spectra, and optical temperature sensing performances under the excitation of 980 nm laser were investigated systematically. Broadband near-infrared (˜1.55 μm, FWHM˜90 nm) emission and strong visible up-conversion (˜550 nm) emission were observed under the 980 nm excitation in the ceramics at room temperature. Near-infrared emission and visible up-conversion emission became stronger with increasing (Na0.5Er0.5)TiO3 concentration below quenching point above which it will degrade. The optimal emission intensity was obtained when (Na0.5Er0.5)TiO3 content was 7 mol%. These ceramics with excellent ferro-/piezoelectric and photoluminescence properties may be useful for ultrasonic transducer, optical temperature sensor, optical amplifier, and other relative applications.

Microwave dielectric properties of low-fired Mg1.9Cu0.1SiO4–(La0.5Na0.5)TiO3 composite ceramics

Mg2−xCuxSiO4 (0 ≤ x ≤ 0.2) ceramics were fabricated by the traditional solid-state process. The results revealed that solid solution was formed at x ≤ 0.2 by substitution Cu2+ for Mg2+ and the sintering temperature was lowered from 1500 to 1200 °C. LiF-doped (1 − y)Mg1.9Cu0.1SiO4–y(La0.5Na0.5)TiO3 (0.1 ≤ y ≤ 0.4) composite ceramics were obtained at a temperature range from 890 to 1000 °C. As increasing (La0.5Na0.5)TiO3 content y, the τf values showed a continuous positive increase. The 0.8Mg1.9Cu0.1SiO4–0.2(La0.5Na0.5)TiO3 composite ceramics with 4.0 wt% LiF sintered at 950 °C possess excellent microwave dielectric properties of εr = 13.3, Q × f = 14,400 GHz, and τf = 6 ppm/°C.

Structure and microwave dielectric properties of (1–x)Nd(Zn0.5Ti0.5)O3–xCa0.61Nd0.26TiO3 ceramics

Structure and microwave dielectric properties of (1−x)Nd(Zn0.5Ti0.5)O3–xCa0.61Nd0.26TiO3 (0.2≤x≤0.8) ceramics prepared by the conventional solid-state reaction route were investigated in detail. It was found that the crystal structure and microwave dielectric properties depended strongly on Ca0.61Nd0.26TiO3 content. In the whole investigated compositional range, the complete solid solutions with perovskite structure were formed together with a small amount of Zn2TiO4 secondary phase. However, a phase transformation from monoclinic to orthorhombic structure was also observed when x>0.6, accompanying with the disappearance of cation ordering. With the increase of Ca0.61Nd0.26TiO3 addition, both the grain size and the dielectric constant (εr) increased. The quality factor (Q×f) was closely related to the grain size and cation ordering of the ceramics. The drastic drop in the temperature coefficient of resonant frequency (τf) might be attributed to the elimination of cation ordering. After being sintered at 1375°C for 4h, 0.4Nd(Zn0.5Ti0.5)O3–0.6Ca0.61Nd0.26TiO3 exhibited high density, uniform microstructure and excellent microwave dielectric properties of εr=56.3, Q×f= 54,400GHz and τf=+0.3ppm/°C.

Studies on room temperature multiferroic properties of xBi0.5Na0.5TiO3-(1-x)NiFe2O4 ceramics

Multiferroic ceramics xBi0.5Na0.5TiO3-(1-x)NiFe2O4 (x = 0–1) have been prepared by a sol–gel method. Crystal structures were investigated by X-ray diffraction. The results show the samples are pure phases and increasing Bi0.5Na0.5TiO3 content induces a gradual phase transformation from spinel to perovskite structure. Scanning electron microscopy micrographs also present the size and structure of the samples. Results from energy dispersive spectrometer confirm the stoichiometry of the compound. Both of the data are proved to agree with the results of X-ray diffraction. All of the samples display the evident ferromagnetic properties at 300 K and the saturation magnetization almost linearly varies with the increasing of x. The room temperature polarization-electric field loops were examined. Compared with pure NiFe2O4, superior ferroelectric properties are obtained with increasing maximum of polarization as the content of Bi0.5Na0.5TiO3 increases. Dielectric properties were also studied. The dielectric constant is proved to increase as Bi0.5Na0.5TiO3 content increases at room temperature and the dielectric loss decreases as Bi0.5Na0.5TiO3 doped in NiFe2O4. In addition, some of samples exhibit the effect of magnetoelectric coupling.

Microwave Dielectric Properties of (Ca&lt;sub&gt;0.&lt;/sub&gt;&lt;sub&gt;8&lt;/sub&gt;Sr&lt;sub&gt;0.&lt;/sub&gt;&lt;sub&gt;2&lt;/sub&gt;)&lt;sub&gt;x&lt;/sub&gt;(Li&lt;sub&gt;0.&lt;/sub&gt;&lt;sub&gt;5&lt;/sub&gt;Nd&lt;sub&gt;0.&lt;/sub&gt;&lt;sub&gt;5&lt;/sub&gt;)&lt;sub&gt;1-&lt;/sub&gt;&lt;sub&gt;x&lt;/sub&gt;TiO&lt;sub&gt;3&lt;/sub&gt; Ceramics

Microwave dielectric properties and microstructures have been investigated in the x Ca0.8Sr0.2TiO3 − (1−x) Li0.5Nd0.5TiO3 ceramic system. In the entire composition range, a single solid solution in the ceramic system was formed with the orthorhombic perovskite structure. As the Ca0.8Sr0.2TiO3 content of the ceramic system increased from 0.1 to 0.3, the dielectric constant (εr) increased from 114 to 144, the product (Qf) of quality factor (Q) and frequency (f) from 995 to 1,121 GHz, and the temperature coefficient of resonant frequency (τf) value from-83 to 94 ppm/°C, respectively. Simultaneously, the observed polarizabilities and the theoretical polarizability increased with rise in the Ca0.8Sr0.2TiO3 content. The τf value increased linearly with the increasing unit-cell volume. For practical application, a near-zero τf in the 0.2Ca0.8Sr0.2TiO3 −0.8Li0.5Nd0.5TiO3 ceramic with a Qf value of 1,025 GHz and a εr value of 132 were obtained at the sintering temperature of 1300°C for 4 h.

Microwave dielectric properties of (1 − x)Mg(Sn0.05Ti0.95)O3–x(Ca0.8Sr0.2)TiO3–y wt% ZnNb2O6 ceramics with near-zero temperature coefficient

The microstructures and the microwave dielectric properties of (1 − x)Mg(Sn0.05Ti0.95)O3–x(Ca0.8Sr0.2)TiO3−y wt% ZnNb2O6 (x = 0.05–0.08, y = 2–8) ceramics system prepared by conventional solid-state route were investigated. The crystalline phases and the microstructures of the ceramics were characterized by means of X-ray diffraction and scanning electron microscopy. Zn2+ partially replaced Mg2+ in Mg(Sn0.05Ti0.95)O3 and formed the ilmenite-type (Mg1−δZnδ)(Sn0.05Ti0.95)O3 phase. Second phase (Mg1−δZnδ)(Sn0.05Ti0.95)2O5 increased remarkably when excess ZnNb2O6 added. ZnNb2O6 as additives could not only effectively lower the sintering temperature of the ceramics to 1320 °C, but also promote the densification. The microwave dielectric properties of specimens were strongly related to ZnNb2O6 and (Ca0.8Sr0.2)TiO3 content. The optimized microwave dielectric properties with e r ~ 22.13, Q × f value ~60,613(at 7 GHz) and τ f value ~0.4 ppm/ °C were achieved for (1 − x)Mg(Sn0.05Ti0.95)O3–x(Ca0.8Sr0.2)TiO3–y wt% ZnNb2O6 (x = 0.07, y = 4) sintered at 1320 °C for 2 h.

Structure, dielectric properties, and applications of (Na0.5Sm0.5)TiO3-modified (Mg0.95Ni0.05)TiO3 ceramics at microwave frequency

The effect of (Na0.5Sm0.5)TiO3 addition on the microwave dielectric properties of (Mg0.95Ni0.05)TiO3 ceramics was investigated. The (Na0.5Sm0.5)TiO3 content plays a significant role in improving the dielectric properties. Microwave dielectric measurements show an increase in the dielectric constant (ϵr) and temperature coefficient of the resonant frequency (τf) and a decrease in the quality factor (Q×f) with increasing (Na0.5Sm0.5)TiO3 content. By increasing the (Na0.5Sm0.5)TiO3 content, not only could the τf of the ceramics be turned to a near-zero τf value (∼1.1ppm/°C) at x=0.19, a substantial Q×f (∼93,000GHz) and ϵr (∼26.2) could also be achieved simultaneously.

Li fast ion conductive La0.56Li0.33TiO3 inlaid LiFePO4/C microspheres with enhanced high-rate performance as cathode materials

Monodisperse spherical La0.56Li0.33TiO3 inlaid LiFePO4/C composites with various La0.56Li0.33TiO3 content (from 0wt.% to 3wt.%) are firstly prepared by an ammonia assisted hydrothermal route. The compositions, morphology and structure of samples are characterized by means of inductively coupled plasma (ICP), X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), respectively. The results reveal that nano La0.56Li0.33TiO3 particles inlay on the surface of spherical LiFePO4, which is coated by a continuous and uniform carbon layer with the thickness of 1∼2nm. The charge/discharge tests and electrochemical impedance spectroscopy (EIS) measurements indicate that the kinetics of La0.56Li0.33TiO3 inlaid LiFePO4/C is better than that of LiFePO4/C. With the change of La0.56Li0.33TiO3 content, 2wt.% La0.56Li0.33TiO3 inlaid LiFePO4/C composites reveal a excellent high-rate capability and cycling stability. The initial discharge capacity of the sample is 126.3 and 108.9mAh/g, and the capacity retention achieves as high as 98.3% and 88.8% till 100 cycles at 5C and 200 cycles at 10C, respectively. Furthermore, it still exhibits a high discharge capacity of 62.3mAh/g even at high rate of 30C. The improved electrochemical performance of La0.56Li0.33TiO3 inlaid LiFePO4/C composites can be attributed to reduce the charge transfer resistance and enhance the transfer kinetics of both the lithium ions and electrons.

Uniaxial Stress Dependence of the Permittivity and the Hardening Effect in the Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 System

The dependence of the permittivity on the uniaxial compressive stress was investigated for the case of Na0.5Bi0.5TiO3–K0.5Bi0.5TiO3 ceramics. For the morphotropic sample the results showed a strong increase in the stress dependence compared to pure Na0.5Bi0.5TiO3. Nevertheless, a threshold stress was observed, below which the domain switching was hindered. The threshold stress value and, thus, the “hardness” of the materials increased with increasing K0.5Bi0.5TiO3 content. In the “hard” tetragonal samples the permittivity increased with the stress loading; however, if the mechanical load exceeded a threshold level, the “hardening” effect vanished. The results are discussed in terms of the defect dipole model for the stabilization of the domain configuration. The stabilization was the highest in pure K0.5Bi0.5TiO3, for which a poled remanent state was preserved at stresses higher than 200 MPa.

Crystal structure and dielectric properties of (1−x)SrTiO3-xCa0.4Sm0.4TiO3 ceramic system at microwave frequencies

(1−x)SrTiO3-xCa0.4Sm0.4TiO3 (0.6 ≤ x ≤ 0.9) ceramics are prepared through the conventional solid-state route. Powders are calcined at 1200 °C and sintered at 1400–1500 °C. High density, CaTiO3-like perovskite structures are obtained in the range 0.6 ≤ x ≤ 0.9. The phase purity, microstructures and microwave dielectric properties are investigated. With an increase of Ca0.4Sm0.4TiO3 content, the dielectric constant (εr) decreases, which is dependent on the difference of ionic polarizability between Ca0.4Sm0.4TiO3 and SrTiO3. The product of dielectric Q value and resonant frequency (Q∙f) increases up to x = 0.8, and then decreases due to the abnormal grain growth. The variation of temperature coefficient of resonant frequency (τf) with B-site bond valence and tolerance factor (t) is discussed by using the theory of bond valence and the changes of tolerance factor in perovskite structure. The (1−x)SrTiO3-xCa0.4Sm0.4TiO3 (0.6 ≤ x ≤ 0.9) ceramics show the dielectric properties of εr ∼ 101.4–142.7, Q∙f ∼ 1999.5–5986.3 GHz (at 2.8–4 GHz) and τf ∼ 359.8–199.6 ppm/°C at different sintering temperatures of 1400–1500 °C for 4 h.

Microwave Dielectric Characteristics of Calcium Titanate-Lithium Lanthanum Titanate Ceramics

The microwave dielectric characteristics, microstructure and physical properties of (1−x)CaTiO3−x(Li0.5La0.5)TiO3 (0.08≤x≤0.9) ceramics (abbreviated 92CT-LLT through 10CT-LLT) prepared by conventional solid-state routes were investigated. Increasing the proportion of (Li0.5La0.5)TiO3 compared to CaTiO3 decreased the sintering temperature of ceramic bodies by 50°C, with achievement of optimum density at 1200°C and formation of dense microstructure due to liquid phase development. In the (1−x)CT−xLLT system, the microwave dielectric properties can be effectively controlled by varying the (Li0.5La0.5)TiO3 content to form favourable secondary phase and microstructure. The best combination of microwave dielectric characteristics was obtained in samples of 50CT-LLT ceramic (x = 0.5) sintered at 1200°C/2 h, with dielectric constant er = 14.1, low dielectric loss = 0.000021 and quality factor Qxf = 364, 524 at 8 GHz.

Dielectric properties and crystal structure of (1 − &lt;i&gt;y&lt;/i&gt;)(Mg&lt;sub&gt;0.95&lt;/sub&gt;Ni&lt;sub&gt;0.05&lt;/sub&gt;)&lt;sub&gt;4&lt;/sub&gt;Ta&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;9&lt;/sub&gt;–&lt;i&gt;y&lt;/i&gt;(Ca&lt;sub&gt;0.8&lt;/sub&gt;Sr&lt;sub&gt;0.2&lt;/sub&gt;)TiO&lt;sub&gt;3&lt;/sub&gt; ceramics

The microwave dielectric properties and microstructures of (1 − y)(Mg0.95Ni0.05)4Ta2O9–y(Ca0.8Sr0.2)TiO3 ceramics prepared using a mixed oxide route were investigated. (Mg0.95Ni0.05)4Ta2O9 has a dielectric constant (εr) of ~12.23, a high quality factor (Q×f) of ~442,092 GHz, and a temperature coefficient of resonant frequency (τf) of ~−55 ppm/°C. To produce a temperature-stable material, Ca0.8Sr0.2TiO3, which has a large positive τf value of 990 ppm/°C, was added to (Mg0.95Ni0.05)4Ta2O9. The temperature coefficient of resonant frequency increased with increasing Ca0.8Sr0.2TiO3 content, going through nearly zero at y = 0.7. The microwave dielectric material 0.3(Mg0.95Ni0.05)4Ta2O9–0.7(Ca0.8Sr0.2)TiO3 has an excellent combination of microwave dielectric properties: εr ~ 29.8, Q×f ~ 226,000 GHz (at 9 GHz), and τf ~ −2.38 ppm/°C sinter at 1350°C. It is proposed as a candidate material for industrial, scientific and medical band components and Global Position System antennas.

Lead-free piezoelectric ceramics based on (0.97 − x)K0.48Na0.52NbO3-0.03Bi0.5(Na0.7K0.2Li0.1)0.5ZrO3-xB0.5Na0.5TiO3 ternary system

In this work, the ternary system of potassium-sodium niobate has been designed to enhance the piezoelectric properties without sacrificing the Curie temperature greatly, and (0.97 − x)K0.48Na0.52NbO3-0.03Bi0.5(Na0.7K0.2Li0.1)0.5ZrO3-xB0.5Na0.5TiO3 ceramics have been prepared by the conventional solid-state method. The effect of B0.5Na0.5TiO3 content on the microstructure and electrical properties of the ceramics is studied. The phase diagram shows a phase boundary of the rhombohedral-tetragonal (R-T) phase coexistence in the composition range of 0.5% &amp;lt; x &amp;lt; 1.5%, and then an enhanced dielectric, ferroelectric, and piezoelectric behavior is obtained at such a phase boundary zone. The ceramic with x = 0.01 has an optimum electrical behavior of d33 ∼ 285 pC/N, kp ∼ 0.40, εr ∼ 1235, tan δ ∼ 0.031, Pr ∼ 14.9 μC/cm2, and Ec ∼ 15.2 kV/cm, together with a high Curie temperature of ∼347 °C. The large d33 in such a ternary system is due to a composition-induced R-T phase transition and a higher ɛrPr, and the thermal stability performance is strongly dependent on the phase structure. As a result, the design of the ternary system is an effective way to enhance the piezoelectric properties of potassium-sodium niobate materials.

Role of amorphous Pb(Zr,Ti)O3 (PZT) in determining the ferroelectric properties of PZT-blended poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE) thin films

Precursor films based on poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) and P(VDF-TrFE) blended with Pb(Zr,Ti)O3 were deposited on Si (100) substrates by spin-coating, and subsequently annealed at 443 K for 0.5 h. These films were then characterized using X-ray diffraction, atomic force microscopy and capacitance-voltage curves. Blending the precursor films of Pb(Zr,Ti)O3 with P(VDF-TrFE) led to the formation of an amorphous oxide whose concentration was proportional to the Pb(Zr,Ti)O3 content. This resulted in extension of the memory-window width with a large voltage difference ranging from 0.07 V to 4.5 V for metal-ferroelectric-silicon capacitors. Moreover, the formation of the amorphous oxide resulted in parallel shifts toward positive or negative voltages in the capacitance-voltage curves because of the fixed negative or positive charge of the oxide at the ferroelectric/Si-substrate interface. These tunable ferroelectric properties open up possibilities for diverse applications and are essential for functional devices, as well as for the commercialization of nonvolatile high-density FeRAM devices.

Effect of Reoxidation Temperature on Electrophysical Properties of High-T&lt;sub&gt;C&lt;/sub&gt; Barium Titanate-Based PTCR Ceramics

Ceramic samples of (1 x)BaTiO3–xNa0.5Bi0.5TiO3 system were prepared by sintering in reducing atmosphere of N2/H2 and were subsequently reoxidized in air. The influence of reoxidation temperature firing on the PTCR effect of (1 x)BaTiO3–xNa0.5Bi0.5TiO3 ceramics was investigated. The effect of Na0.5Bi0.5TiO3 concentration on resistivity and microstructure of the reoxidized samples was investigated by means of complex impedance spectroscopy and scanning electron microscopy. It has been found that the grain size decreases with the increase in Na0.5Bi0.5TiO3 content. The values of minimum ρmin and maximum ρmax resistivities of the samples were observed to increase with the increase in reoxidation temperature in the 600 – 1000°C temperature range. It was shown that with increasing in reoxidation temperature of (1-x)BaTiO3-xNa0.5Bi0.5TiO3 solid solutions, potential barrier at grain boundaries increases.

Synthesis and electrical properties of (BaTiO3)1 −x (K0.5Bi0.5TiO3) x solid solutions

(BaTiO3)1 − x(K0.5Bi0.5TiO3)x solid solutions exhibiting positive temperature coefficient of resistance behavior have been prepared using BaTiO3 presynthesized through oxalate coprecipitation. The peak in their dielectric permittivity has been shown to shift to higher temperatures (above 120°C) with increasing x. We have examined the effect of K0.5Bi0.5TiO3 content on the microstructure of the (BaTiO3)1 − x(K0.5Bi0.5TiO3)x solid solutions. The results demonstrate that, with increasing x, both the minimum and maximum resistivities of the materials in the temperature range of their positive temperature coefficient of resistance behavior increase. The materials prepared using barium titanate presynthesized by the oxalate route have higher Curie temperatures and temperatures where they exhibit positive temperature coefficient of resistance behavior and lower minimum resistivities than do the materials prepared by solid-state reactions.

Dielectric and Magnetic properties of (1 − x)BiFeO3–xBa0.8Sr0.2TiO3 ceramics

The polycrystalline samples of (1−x)BiFeO3–xBa0.8Sr0.2TiO3 (x=0, 0.1, 0.2, 0.25, 0.3, 0.4 and x=1) were prepared by the conventional solid state reaction method. The effect of substitution in BiFeO3 by Ba0.8Sr0.2TiO3 on the structural, dielectric and magnetic properties was investigated. X-ray diffraction study showed that these compounds crystallized at room temperature in the rhombohedral distorted perovskite structure for x≤0.3 and in cubic one for x=0.4. As Ba0.8Sr0.2TiO3 content increases, the dielectric permittivity increases. This work suggests also that the Ba0.8Sr0.2TiO3 substitution can enhance the magnetic response at room temperature. A remanent magnetization Mr and a coercive magnetic field HC of about 0.971emu/g and 2.616kOe, respectively were obtained in specimen with composition x=0.1 at room temperature.

Influences of Ba/Ti Ratios on the Positive Temperature Coefficient of Resistivity Effect of Y-Doped BaTiO3-(Bi1/2Na1/2)TiO3 Ceramics

Y-doped (1−x mol%)BaTiO3–x mol%(Bi1/2Na1/2)TiO3 (BBNTx) lead-free positive temperature coefficient of resistivity (PTCR) ceramics were prepared using a conventional solid sintering method. The Ba/Ti ratio was adjusted to obtain the optimized PTCR property. The results show that all 0.2 mol% Y-doped BBNT15 samples with various Ba/Ti ratios have formed a single tetragonal perovskite phase by sintering in an N2 atmosphere. The sample with 5 mol% (Bi1/2Na1/2)TiO3 has only a minor PTCR effect (maximum resistivity [ρmax]/minimum resistivity [ρmin]) when sintered in N2. However, the PTCR effect is enhanced over 3.0 orders of magnitude when the (Bi1/2Na1/2)TiO3 content is >8 mol%. The PTCR characteristics of the samples with Ti excess are superior to those with Ba excess. The optimum composition of 0.2 mol% Y-doped BBNT15 with Ba/Ti=0.99, sintered at 1250°C for 3 h in an N2 atmosphere, has a low room-temperature resistivity (ρ25) of ∼100 Ω·cm and a high PTCR effect of ∼4.8 orders of magnitude with Tc around 190°C.

Temperature Compensating Microwave Dielectric Based on the (Mg0.95Ni0.05)TiO3–(La0.5Na0.5)TiO3 Ceramic System

The microstructures and microwave dielectric properties of the novel temperature‐compensated composite ceramic (1−x)(Mg0.95Ni0.05)TiO3–x(La0.5Na0.5)TiO3 were investigated. Dense and mixed phase samples were produced in the range of 0.05≤x≤0.9. When the x value increased, the quality factor (Q×f) decreased nonlinearly while the dielectric constant (ɛr) steadily increased almost linearly due to the compensation effect. The temperature coefficient of resonant frequency (τf) was remarkably improved with an increase of (La0.5Na0.5)TiO3 content. With x=0.13, a dielectric constant (ɛr) of 23.22, a Q×f value of 86,500 GHz, and a τf value of 2.8 ppm/°C was obtained for 0.87(Mg0.95Ni0.05)TiO3–0.13(La0.5Na0.5)TiO3 ceramics sintered at 1275°C for 4 h. Moreover, a band‐pass filter with traditional hairpin resonators with a center frequency of 2.4 GHz was designed and fabricated using the proposed dielectric ceramic to study its performance.