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1.
Grain size control of lead-free Li0.06(Na0.5K0.5)0.94NbO3 piezoelectric ceramics by Ba and Ti doping
Ken-ichi Kakimoto Kiyotaka Ando Hitoshi Ohsato 《Journal of the European Ceramic Society》2010,30(2):295-299
In this study, Ba- and Ti-doped Li0.06(Na0.5K0.5)0.94NbO3 [(1 ? x)Li0.06(Na0.5K0.5)0.94NbO3–xBaTiO3 (x = 0–0.07)] ceramics were prepared by using conventional solid state reaction method, and the microstructure and electric properties of these samples were investigated. The grain size distribution of non-doped Li0.06(Na0.5K0.5)0.94NbO3 ceramics was relatively wide. The microstructure was composed of grains ranging 1.1–5.0 μm in size. However, with increasing Ba and Ti content, the grain size distribution became narrow and the average grain size decreased from 2.0 to 0.9 μm in size. In particular, the microstructure of x = 0.07 sample was composed of grains ranging 0.5–2.2 μm in size. As a result, the frequency dispersion of dielectric constant for the (1 ? x)Li0.06(Na0.5K0.5)0.94NbO3–xBaTiO3 (x = 0–0.07) ceramics was reduced and the mechanical quality factor Qm was enhanced with increasing Ba and Ti content. 相似文献
2.
Ali Hussain Chang Won Ahn Aman Ullah Jae Shin Lee Ill Won Kim 《Ceramics International》2012,38(5):4143-4149
Lead-free piezoelectric (1 ? x)Bi0.5(Na0.78K0.22)0.5TiO3–xK0.5Na0.5NbO3 (BNKT–xKNN, x = 0–0.10) ceramics were synthesized using a conventional, solid-state reaction method. The effect of KNN addition on BNKT ceramics was investigated through X-ray diffraction (XRD), dielectric, ferroelectric and electric field-induced strain characterizations. XRD revealed a pure perovskite phase with tetragonal symmetry in the studied composition range. As the KNN content increased, the depolarization temperature (Td) as well as maximum dielectric constant (?m) decreased. The addition of KNN destabilized the ferroelectric order of BNKT ceramics exhibiting a pinched-type hysteresis loop with low remnant polarization (11 μC/cm2) and small piezoelectric constant (27 pC/N) at 3 mol% KNN. As a result, at x = 0.03 a significant enhancement of 0.22% was observed in the electric field-induced strain, which corresponds to a normalized strain (Smax/Emax) of ~434 pm/V. This enhancement is attributed to the coexistence of ferroelectric and non-polar phases at room temperature. 相似文献
3.
《Journal of the European Ceramic Society》2017,37(4):1459-1466
Lead-free 0.94NBT-0.06BT-xLa ceramics at x = 0.0–1.0 (%) were synthesized by a conventional solid-state route. XRD shows that the compositions are at a morphotropic phase boundary where rhombohedral and tetragonal phases coexist. With increasing La3+ content pyroelectric coefficient (p) and figures of merits greatly increase; however, the depolarization temperature (Td) decreases. p is 7.24 × 10−4C m−2 °C−1 at RT at x = 0.5% and 105.4 × 10−4C.m−2 °C−1 at Td at x = 0.2%. Fi and Fv show improvements at RT from 1.12 (x = 0%) to 2.65 (x10 −10 m v−1) (x = 0.5%) and from 0.021 to 0.048 (m2.C−1) respectively. Fi and Fv show a huge increase to 37.6 × 10−10 m v−1 and 0.56 m2 C−1 respectively at Td at x = 0.2%. FC shows values of 2.10, 2.89, and 2.98 (x10−9C cm−2 °C−1) at RT at 33, 100 and 1000 (Hz) respectively. Giant pyroelectric properties make NBT-0.06BT-xLa at x = 0.2% and 0.5% promising materials for many pyroelectric applications. 相似文献
4.
5.
《Ceramics International》2016,42(3):4532-4538
The structural, thermal and electrochemical properties of the perovskite-type compound La1−xNdxFe0.5Cr0.5O3 (x=0.10, 0.15, 0.20) are investigated by X-ray diffraction, thermal expansion, thermal diffusion, thermal conductivity and impedance spectroscopy measurements. Rietveld refinement shows that the compounds crystallize with orthorhombic symmetry in the space group Pbnm. The average thermal expansion coefficient decreases as the content of Nd increases. The average coefficient of thermal expansion in the temperature range of 30–850 °C is 10.12×10−6, 9.48×10−6 and 7.51×10−6 °C−1 for samples with x=0.1, 0.15 and 0.2, respectively. Thermogravimetric analyses show small weight gain at high temperatures which correspond to filling up of oxygen vacancies as well as the valence change of the transition metals. The electrical conductivity measured by four-probe method shows that the conductivity increases with the content of Nd; the electrical conductivity at 520 °C is about 4.71×10−3, 6.59×10−3 and 9.62×10−3 S cm−1 for samples with x=0.10, 0.15 and 0.20, respectively. The thermal diffusivity of the samples decreases monotonically as temperature increases. At 600 °C, the thermal diffusivity is 0.00425, 0.00455 and 0.00485 cm2 s−1 for samples with x=0.10, 0.15 and 0.20, respectively. Impedance measurements in symmetrical cell arrangement in air reveal that the polarization resistance decreases from 55 Ω cm−2 to 22.5 Ω cm−2 for increasing temperature from 800 °C to 900 °C, respectively. 相似文献
6.
《Journal of the European Ceramic Society》2014,34(1):37-43
Thick films with compositions (1 − x)(0.94Bi1/2Na1/2TiO3–0.06BaTiO3)–x(K0.5Na0.5NbO3) (x = 0, 0.03, 0.09 and 0.18) have been prepared and their structural and electrical properties have been investigated. Dielectric properties show that these films are well suited for high-temperature applications due to their low variance in permittivity (<15%) over large temperature ranges. The thick film with x = 0.18 offers an operational temperature range from room temperature to 350 °C. Films with x = 0.03 and 0.09 also possess a stabile permittivity up to 400 °C. The improvement in the thermal stability of the permittivity is attributed to the addition of K0.5Na0.5NbO3 which leads to breaking of the long-range order in the materials. However, the polarizability of the materials was found to decrease possibly due to the clamping effect of the substrate. The characteristics of each film are discussed based on dielectric and electrical properties. 相似文献
7.
Weberites and pyrochlores (A2B2O7), both fluorite-related superstructures, are attractive dielectric ceramics due to their ability to accommodate diverse cations, thus allowing their properties to be tailored. This study focuses on the fundamental understanding of the structure–dielectric property relationships in fluorite-related oxides. Specifically, Ln3NbO7 and Ln2(Ln′0.5Nb0.5)2O7 (where the ionic radius of Ln′ is smaller than that of Ln) compounds are investigated. It has been previously shown that weberite-type Ln3NbO7 exhibits a composition dependent dielectric relaxation above room temperature. It is here shown that a dielectric relaxation also occurs in La2(Ln′0.5Nb0.5)2O7 (Ln′ = Yb3+, Er3+, and Dy3+) compounds near or below ?158 °C. The temperature, at which the maximum permittivity occurs, is different for different compositions (?132 °C for La2(Yb0.5Nb0.5)2O7, ?197 °C for La2(Er0.5Nb0.5)2O7, and ?187 °C for La2(Dy0.5Nb0.5)2O7 at 1 MHz) and is correlated with the distortion of the NbO6 octahedra. The room temperature dielectric permittivity of all three compounds was measured to be between 40 and 50 at 1 MHz. 相似文献
8.
《Journal of the European Ceramic Society》2017,37(10):3303-3311
A series of (1-x)(0.65BaTiO3-0.35Bi0.5Na0.5TiO3)-xNa0.73Bi0.09NbO3 ((1-x)BBNT-xNBN) (x = 0–0.14) ceramics were designed and fabricated using the conventional solid-state sintering method. The microstructure, dielectric property, relaxor behavior and energy storage property were systematically investigated. X-ray diffraction results reveal a pure perovskite structure and dielectric measurements exhibit a relaxor behavior for the (1-x)BBNT-xNBN ceramics. The slim polarization electric field (P-E) loops were observed in the samples with x ≥ 0.02 and the addition of Na0.73Bi0.09NbO3 (NBN) could decrease the remnant polarization (Pr) of the (1-x)BBNT-xNBN ceramics obviously. The sample with x = 0.08 exhibits the highest energy storage density of 1.70 J/cm3 and the energy storage efficiency of 82% at 172 kV/cm owing to its submicron grain size and high relative density. These results show that the (1-x)BBNT-xNBN ceramics may be promising lead-free materials for high energy storage density capacitors. 相似文献
9.
《Journal of the European Ceramic Society》2005,25(4):489-499
The oxygen permeability of mixed-conducting Sr1−xCaxFe1−yAlyO3−δ (x=0–1.0; y=0.3–0.5) ceramics at 850–1000 °C, with an apparent activation energy of 120–206 kJ/mol, is mainly limited by the bulk ionic conduction. When the membrane thickness is 1.0 mm, the oxygen permeation fluxes under pO2 gradient of 0.21/0.021 atm vary from 3.7×10−10 mol s−1 cm−2 to 1.5×10−7 mol s−1 cm−2 at 950 °C. The maximum solubility of Al3+ cations in the perovskite lattice of SrFe1−yAlyO3−δ is approximately 40%, whilst the brownmillerite-type solid solution formation range in Sr1−xCaxFe0.5Al0.5O3−δ system corresponds to x>0.75. The oxygen ionic conductivity of SrFeO3-based perovskites decreases moderately on Al doping, but is 100–300 times higher than that of brownmillerites derived from CaFe0.5Al0.5O2.5+δ. Temperature-activated character and relatively low values of hole mobility in SrFe0.7Al0.3O3−δ, estimated from the total conductivity and Seebeck coefficient data, suggest a small-polaron mechanism of p-type electronic conduction under oxidising conditions. Reducing oxygen partial pressure results in increasing ionic conductivity and in the transition from dominant p- to n-type electronic transport, followed by decomposition. The low-pO2 stability limits of Sr1−xCaxFe1−yAlyO3−δ seem essentially independent of composition, varying between that of LaFeO3−δ and the Fe/Fe1−γO boundary. Thermal expansion coefficients of Sr1−xCaxFe1−yAlyO3−δ ceramics in air are 9×10−6 K−1 to 16×10−6 K−1 at 100–650 °C and 12×10−6 K−1 to 24×10−6 K−1 at 650–950 °C. Doping of SrFe1−yAlyO3−δ with aluminum decreases thermal expansion due to decreasing oxygen nonstoichiometry variations. 相似文献
10.
R. Lowndes F. Azough R. Cernik R. Freer 《Journal of the European Ceramic Society》2012,32(14):3791-3799
Ca(1?x)Nd2x/3TiO3 microwave dielectric ceramics were prepared by the mixed oxide route; powders were calcined at 1100 °C and sintered at 1450–1500 °C. High density, single phase products were obtained for all compositions. Grain sizes ranged from 1 μm to 100 μm. There was evidence of significant discontinuous grain growth in mid range compositions; all ceramics were characterised by complex domain structures. With increasing Nd content there was a evidence of a transition from an orthorhombic Pbnm structure to a monoclinic C2/m structure. This was accompanied by a decrease in relative permittivity (?r) from 180 to 78, and decrease in the temperature coefficient of resonant frequency (τf) from +770 ppm K?1 to +200 ppm K?1. The product of dielectric Q value and resonant frequency (Q × f) varied in a grossly non-systematic way, exhibiting a peak at 13,000 GHz in Ca0.7Nd0.2TiO3. 相似文献
11.
Mei-Yu Chen Ching Yu Chiu Chia-Ta Chia J.F. Lee J.J. Bian 《Journal of the European Ceramic Society》2010,30(2):335-339
A-site deficient perovskite compounds, La(2?x)/3NaxTiO3 (0.02 ≤ x ≤ 0.5) and Nd(2?x)/3LixTiO3 (0.1 ≤ x ≤ 0.5) microwave ceramics, were investigated by Raman scattering. Nd(2?x)/3LixTiO3 (0.1 ≤ x ≤ 0.5) was also investigated by extended X-ray absorption fine structure (EXAFS) measurement. The Raman shifts of the E (239 cm?1) and A1 (322 cm?1) modes of La(2?x)/3NaxTiO3 were found to decrease with x. However, the E (254 cm?1) and A1 (338 cm?1) of Nd(2?x)/3LixTiO3 were found to blueshift with x, which was caused by Li substitution. The redshift of the A1 (471 cm?1) phonon of Nd(2?x)/3LixTiO3 (0.1 ≤ x ≤ 0.3) indicates that O–Ti–O bonding forces lessen with Li concentration, which is consistent with the EXAFS result that Ti–O bond lengths increase for 0.1 ≤ x ≤ 0.3. For x > 0.3, the EXAFS result shows that Ti–O bond lengths decrease. Moreover, Ti–O bond lengths show strong correlation with the microwave dielectric constants of Nd(2?x)/3LixTiO3. 相似文献
12.
Jeong-Ho Cho Yoo-Jung Choi Young-Jin Lee Young-Hun Jeong Myoung-Pyo Chun Joong-Hee Nam Byung-Ik Kim 《Ceramics International》2012
Li0.02(KxNa1?x)0.98NbO3(x = 0.35–0.55) ceramics were prepared using the conventional solid state sintering method. The thermal behaviors of Li-modified (KxNa1?x)NbO3 ceramics were investigated from ?30 to 150 °C, and the effect of Na/K ratio in (KxNa1?x)NbO3 ceramics on thermal behavior and electrical properties was also studied. In the case of Li0.02(KxNa1?x)0.98NbO3 ceramics with 0.5 wt.% ZnO, the transition temperature was sharply decreased because of a phase transition as the composition range of x was 0.425–0.475. From the results of the temperature dependence of piezoelectric properties, it is assumed that the Na-rich phase is less stable than the K-rich phase for temperature change. 相似文献
13.
In this work, Na0.5Bi0.5TiO3 (NBT) was used to improve the high temperature dielectric properties of Nb, Co-doped BaTiO3 (BT). Different x was selected (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.2, 0.3, 0.4) to optimize the ratio of BT to NBT in (1 ? x) BT–xNBT solid solution. The dielectric constant of the original X7R material is about 4900 at room temperature, decreasing to 2500 with NBT addition (x = 0.2). Of important is that the temperature stability was improved with dielectric constant variation being less than ±15% up to 160 °C. 相似文献
14.
Dielectric properties of (Zn1/3Nb(2?x)/3Tax/3)0.5(Ti0.8Sn0.1Ge0.1)0.5O2 (x = 0, 1, 2) and/or (Zn1/3Nb1/3Tal/3)0.5(Ti0.8Sn0.2(l?y)Ge0.2y)0.5O2 (y = 0, 0.5, 1) were investigated at the microwave frequencies. For the compositions with single phase of rutile structure, the dielectric constant (K) of specimens was not only dependent on the dielectric polarizabilities, but also on the bond length ratio of apical bond (dapical) to equatorial bond (dequatorial) of oxygen octahedron in the unit cell. Temperature coefficients of the resonant frequencies (TCF) of the specimens with B = Nb5+ and/or M = Sn4+ was larger than those with B = Ta5+ and/or M = Ge4+. These results could be attributed to the changes of the degree of oxygen octahedral distortion. Quality factors (Qf) of the specimens with B = Ta5+ and/or M = Sn4+ were larger than those with B = Nb5+ and/or M = Ge4+. 相似文献
15.
Microwave dielectric properties of low loss microwave dielectric ceramics: A0.5Ti0.5NbO4 (A = Zn,Co)
《Journal of the European Ceramic Society》2014,34(15):3641-3648
The microwave dielectric properties of low-loss A0.5Ti0.5NbO4 (A = Zn, Co) ceramics prepared by the solid-state route had been investigated. The influence of various sintering conditions on microwave dielectric properties and the structure for A0.5Ti0.5NbO4 (A = Zn, Co) ceramics were discussed systematically. The Zn0.5Ti0.5NbO4 ceramic (hereafter referred to as ZTN) showed the excellent dielectric properties, with ɛr = 37.4, Q × f = 194,000 (GHz), and τf = −58 ppm/°C and Co0.5Ti0.5NbO4 ceramic (hereafter referred to as CTN) had ɛr = 64, Q × f = 65,300 (GHz), and τf = 223.2 ppm/°C as sintered individually at 1100 and 1120 °C for 6 h. The dielectric constant was dependent on the ionic polarizability. The Q × f and τf are related to the packing fraction and oxygen bond valence of the compounds. Considering the extremely low dielectric loss, A0.5Ti0.5NbO4 (A = Zn and Co) ceramics could be good candidates for microwave or millimeter wave device application. 相似文献
16.
《Journal of the European Ceramic Society》2014,34(8):1981-1988
La1−x−yCexYbyNbO4 specimens with various Ce and Yb contents were prepared by solid reactions, and their crystal structure, element valence, sinterability and conductivity were investigated. LaNbO4-type single phase was formed at 1200 °C in air, and the lattice of La1−x−yCexYbyNbO4 was distorted from that of LaNbO4 to various extents, depending on the added amount of Ce and Yb. Both La and Nb remained the same valence as they are in LaNbO4; Ce4+, Ce3+ and Yb3+ were detected at room temperature. Highly densified La1−x−yCexYbyNbO4 specimens were achieved by sintering at above 1215 °C in air with conductivity 1–2 orders higher than that of pure LaNbO4 in dry air, wet air and wet 5% H2–N2 atmospheres. The conductivity changed with testing atmosphere owing to the competition of electron and proton conduction, and maximal value 4.7 × 10−4 S cm−1 was obtained in wet air at 900 °C. 相似文献
17.
The structural evolution and microwave dielectric properties of (1 ? x)Li2TiO3 + xMgO system (0 ≤ x ≤ 0.5) have been investigated in this paper. The ordering degree decreased with the increase of MgO content. The microcracks and cleavage on (0 0 1) due to the weak Li–O bonds disappeared with the increase of MgO content. The dielectric constant and temperature coefficient of resonant frequency decreased with the increase of MgO content. The Q × f value increased with x up to x = 0.2 and then decreases with the further increase of x. An excellent combined microwave dielectric properties could be obtained when x = 0.24, ?r = 19.2, Q × f = 106,226 GHz and τf = 3.56 ppm/°C. 相似文献
18.
In this study, the ceramic powders of Ce1?xGdxO2?x/2 and Ce1?xNdxO2?x/2 (x=0.05, 0.10, 0.15, 0.20 and 0.25) were synthesized by ultrasound assisted co-precipitation method. The ionic conductivity was studied as a function of dopant concentration over the temperature range of 300–800 °C in air, using the impedance spectroscopy. The maximum ionic conductivity, σ800 °C=4.01×10?2 Scm?1 with the activation energy, Ea=0.828 kJmol?1 and σ800 °C=3.80×10?2 Scm?1 with the activation energy, Ea=0.838 kJmol?1 were obtained for Ce0.90Gd0.10O1.95 and Ce0.85Nd0.15O1.925 electrolytes, respectively. The average grain size was found to be in the range of 0.3–0.6 μm for gadolinium doped ceria and 0.2–0.4 μm for neodymium doped ceria. The uniformly fine crystallite sizes (average 12–13 nm) of the ultrasound assisted prepared powders enabled sintering of the samples into highly dense (over 95%) ceramic pellets at 1200 °C (5 °C min?1) for 6 h. 相似文献
19.
Shashank Mishra Liliane G. Hubert-Pfalzgraf Stéphane Daniele Marc Rolland Erwann Jeanneau Bernadette Jouguet 《Inorganic chemistry communications》2009,12(2):97-100
In order to obtain a better anhydrous precursor for various applications in materials science and catalysis, thermal dehydration reactions of Y(TFA)3(H2O)3 (TFA = trifluoroacetate) (A) were investigated. Thermal treatment of A at different temperatures under vacuum (5 × 10?2 mm) for several hours failed to give totally anhydrous yttrium trifluoroacetate (as indicated by IR). Two different complexes, a partially dehydrated [Y(μ,η1:η1-TFA)3(THF)(H2O)]1∞·THF (1) and a partially hydrolyzed [Y4(μ3-OH)4(μ,η1:η1-TFA)6(η1-TFA)(η2-TFA)(THF)3(DMSO)(H2O)] · 6THF (2), were obtained with good and moderate yield, respectively, by crystallization of two different thermally treated batches of A from THF (or THF + DMSO) at room temperature. More efficient dehydration of A could be achieved at 200 °C in a furnace, the obtained anhydrous yttrium tris-trifluoroacetate giving Y(TFA)3(THF)2 (3) on crystallization from THF. All the products were characterized by elemental analyses, FT-IR and 1H NMR spectroscopy as well as thermo-gravimetric analysis. In addition, single crystal X-ray structures are reported for 1 and 2, which show either a terminal (η1 and η2) or bridging (μ,η1:η1) bonding behavior of the TFA ligand. 相似文献
20.
The LiMg(1?x)ZnxPO4 ceramics have been prepared by the solid state ceramic route. The LiMg(1?x)ZnxPO4 ceramic retains the orthorhombic structure up to x = 0.2. The compositions with 0.3 ≤ x ≤ 0.8 exist as a mixture of orthorhombic and monoclinic phases. When Mg2+ is fully replaced with Zn2+ (x = 1.0) complete transition to monoclinic phase occurs. The ceramic with x = 0.1 (LiMg0.9Zn0.1PO4) sintered at 925 °C exhibits low relative permittivity (?r) of 6.7, high quality factor (Qu × f) of 99,700 GHz with a temperature coefficient of resonant frequency (τf) of ?62 ppm/°C. The slightly large τf is adjusted nearly to zero with the addition of TiO2. LiMg0.9Zn0.1PO4–TiO2 composite with 0.12 volume fraction TiO2 sintered at 950 °C shows good microwave dielectric properties: ?r = 10.1, Qu × f = 52,900 GHz and τf = ?5 ppm/°C. The ceramic is found to be chemically compatible with silver. 相似文献