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1.
Electrical properties of acceptor (Mn, Mg or Mn+Mg)-doped BaTiO3 ceramic have been studied in terms of oxygen vacancy concentration, various doping levels and electrical degradation behaviors. The solubility limit of Mn on Ti sites was confirmed to be close to or less than 1.0 mol%. Oxygen vacancy concentration of Ba(Ti0.995 –xMg0.005Mnx)O2.995 –y (x = 0, 0.005, 0.01) was estimated to be 50 times greater than that of the un-doped BaTiO3. The leakage current of 0.5 mol% Mn-doped BaTiO3 was stable with time, which was much lower than that of the un-doped BaTiO3. The BaTiO3 specimen co-doped with 0.5 mol% Mg and 1.0 mol% Mn showed the lowest leakage current below 10– 10A. It was confirmed that leakage currents of Mg-doped and un-doped BaTiO3 under dc field are effectively suppressed by Mn co-doping as long as the Mn doping level is greater than Mg contents. 相似文献
2.
Chung-Eun Lee Sun-Ho Kang Dong-Sook Sinn Han-Ill Yoo 《Journal of Electroceramics》2004,13(1-3):785-791
BaTiO3-based multilayer-ceramic capacitors (MLCC) using base metal (Ni) electrodes normally contains Mn and Y each approximately on the order of 0.5 mol%. It is only empirically known that the co-doping of Y and Mn facilitates sintering with the base-metal electrodes as well as improves the device performance and life time. In order to understand the effect of the co-doping, we have measured the electrical conductivity and chemical diffusivity on polycrystalline BaTiO3 that is co-doped with Y and Mn each by 0.5 mol% against oxygen partial pressure at elevated temperatures. It is found that while the n-type conductivity in reducing atmospheres (e.g., Po2 < 10– 6 atm at 1000C) remains similar to that of undoped or acceptor-doped BaTiO3, its p-type conductivity in oxidizing atmospheres (e.g., Po2 > 10– 6at 1000C) is remarkably suppressed compared to the latter. The chemical diffusivity is also similar to that of the latter in magnitude (e.g., 10– 2–10– 5 cm2/s at 1000C), but its trend of variation with oxygen partial pressure is rather opposite. These variations of the conductivity and chemical diffusivity are mainly attributed to Mn ions changing their valence from +2 to +3 to +4 with increasing oxygen partial pressure. It is explained from a defect-chemical view why the codoping of fixed-valent donor (Y) and variable-valent acceptor (Mn) has been practiced in MLCC processing. 相似文献
3.
P-type partial conductivity has been determined on donor (La
Ba
)-doped BaTiO3 in full thermodynamic equilibrium state at a fixed temperature of 1200°C: For the nominal compositions of Ba0.99La0.01Ti0.9975O3, Ba0.99La0.01TiO3 and Ba0.985La0.01TiO3, the p-type conductivity is found to vary with oxygen activity as p = (m/2)(a
O
2/a
O
2*)+1/4 with m 0.01 S cm–1 and a
O
2* 32, 120, 310, respectively, in the a
O
2 region where conventionally the electronic conductivity varies as aO
2
–1/4 and hence, the doped donors are believed to be compensated by cation vacancies (say, [LaBa
] 4[VPrime;Ti]). This experimental fact supports that in the vicinity of the stoichiometric composition of the system which falls approximately at a
O
2 = a
O
2*, while cation vacancy concentration is fixed by the donor concentration, oxygen vacancy concentration in the minority is also essentially fixed, thus, keeping the activity of TiO2 (or BaO) fixed. It is consequently suggested that donor-doped BaTiO3 contains a second phase even in its stoichiometric regime. 相似文献
4.
Thin films of polycrystalline, tetragonal BaTiO3 on oxidized Ti metal substrates were synthesized at 240°C under hydrothermal conditions. Microstructure and electrical properties of the films generated over a four week period of synthesis formed the focus of this study. The films displayed a smooth and shiny surface with a relatively dense structure and no observable cracks. Film thickness reached 0.5 m after two weeks of synthesis and thereafter remained constant. Diameters of the grains on the film surface were in the range of 12 m. It is proposed that initial formation of the BaTiO3 film occurs by reaction of Ba2+ with solubilized titanium oxide on the Ti metal surface followed at later stages by an in-situ growth via reaction of TiOx with Ba2+ diffusing through the BaTiO3 film. X-ray diffraction and Raman spectroscopy indicated that the BaTiO3 films are tetragonal, and the films exhibited typical ferroelectric hysteresis loops at room temperature. However, no evidence of the dielectric anomaly (Curie transition) between 30 and 200°C was observed. Dielectric constant of the films at 1 kHz at room temperature was between 400–500. Both dielectric constant and tan exhibited low dispersion as a function of frequency at temperatures below 150°C, and the dispersion increased with temperature. 相似文献
5.
Defect chemistry of Y doped BaTiO3 was investigated as a function of the Ba/Ti ratio. When the Ba/Ti ratio was greater than unity, Y3 + was substituted for the normal Ti site and the equilibrium conductivity showed a strong evidence of acceptor-doped behavior. With the Ba/Ti ratio < 1, Y3 + was substituted for the Ba site and the equilibrium conductivity showed donor-doped behavior. In the case excess Y2O3 was added to the stoichiometric BaTiO3(Ba/Ti = 1), the conductivity profile showed a donor-doped behavior at low concentrations (< 1.0 mol%), whereas, at higher donor levels (> 2.0 mol%), the equilibrium conductivity minimum shifted toward lower Po2, indicating acceptor doped behavior. 相似文献
6.
The dielectric properties of c-axis epitaxial BaTiO3 thin film on LaAlO3 are investigated at frequencies of 0.5–30 GHz. For the measurements, interdigital capacitors with the Au/Ti electrode configurations of five fingers pairs that are 15 m wide and spaced 2 m apart are prepared by photolithography and lift-off patterning. Finger length varies from 20 to 80 m. The capacitance of epitaxial BaTiO3 films exhibited no frequency dependence up to 10 GHz with the exception of slightly upward tendency of capacitance in BaTiO3 film with a finger length of 80 m due to the self resonant frequency at 20 GHz. The Q-factors of the capacitors, defined as Q = 1/CR, are decreased up to 10 GHz with increased frequency. At 10 GHz, the BaTiO3 film has a tunability [defined as k(V) = [C(0)–C(V)]C(0)] of 1.5% at 15 V, a loss tangent of 0.2 at room temperature. The small tunability can be interpreted as a result of in-plane compressive stress of BaTiO3 film exhibiting large dielectric anisotropy. For the improvement of tunability and dielectric loss in the interdigital BaTiO3 capacitor, the tetragonality (c/a) of epitaxial BaTiO3 film and design of interdigital capacitor should be modified. 相似文献
7.
Donald M. Smyth 《Journal of Electroceramics》2002,9(3):179-186
It has recently been asserted that the donor charge in La+3 -doped BaTiO3 is always compensated by Ti vacancies, and that electrons are never the primary compensating defect. It was also stated that the conductivity observed in reduced, donor-doped BaTiO3 results from the loss of a very small amount of oxygen not directly related to the donor content. However, the observed reproducible and reversable weight loss on reduction, or gain on oxidation, is exactly that expected for a change between ionic and electronic compensation. It corresponds to the loss or gain of the excess oxygen contained in the donor oxide, e.g. LaO1.5 vs. the BaO it replaces. The amount of this weight change is proportional to the donor concentration. This is in agreement with the observation that the equilibrium conductivity in the P(O2)-independent region of electronic compensation is proportional to the donor concentration. Thus the conductivity observed in reduced samples is directly coupled to the donor concentration, and the carrier concentration is equal to the net donor content. In fact, the equilibrium conductivity of donor-doped BaTiO3 conforms to the behavior expected from classical defect chemistry, and exhibits regions of both ionic and electronic compensation of the donor charge, as expected. Phase studies by TEM have shown that donor-doped BaTiO3 sintered in air self-adjusts its composition, by splitting out a second phase if necessary, so that the appropriate amount of compensating Ti vacancies are formed. However, when sintered in a reducing atmosphere, the composition self-adjusts to accommodate charge compensation by electrons. 相似文献
8.
Md. Jawed Ansaree 《Integrated ferroelectrics》2016,176(1):184-201
The reaction of Ba(NO3)2 with TiO2 was studied by thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques up to 1000°C and in nitrogen atmosphere. It was found that the formation of BaTiO3 takes place above 600°C. BaTiO3 powder was prepared by calcination of Ba(NO3)2 and TiO2 precursor mixture at 800°C for 8 h. X-ray diffraction analysis of the synthesized BaTiO3 confirmed the formation of tetragonal phase. Average crystallite size was found to be 44 nm, For the electrical and morphological characterization pellets of the obtained powder were sintered at 1000 °C for 12 h. Scanning electron micrograph (SEM) exhibits spherical and rod shaped grains. The dielectric constant, dissipation factor, complex plane impedance and ac conductivity of the sintered pellet has been measured in the temperature range of 40–600°C and frequency range of 100 Hz–2 MHz. DC conductivity of the sample was obtained from the impedance data. The conductivities (both ac and dc) and relaxation time (τ) exhibit two regions of temperature dependence, namely region I, which represents (280–450°C) and region II, which governs (450-600°C). Conduction and relaxation in both the temperature regions are explained in terms of hopping of electrons and doubly ionized oxygen vacancies (VO??). 相似文献
9.
Effects of mixing methods (mechanical mixing, chemical coating) on microstructure and dielectric properties of Ho, Mg and
Mn doped BaTiO3 have been studied. BaTiO3 particles coated with Ho, Mn and Mg were prepared by a homogeneous precipitation method using urea, and then silica was coated
by the sol-gel technique. The adsorption of additives on the BaTiO3 surface was confirmed. Temperature characteristics of capacitance were satisfied by mechanical mixing and chemical coating
techniques, both of which yield different sintering and microstructure behaviors. Pyrochlore phase (Ho2Ti2O7) was observed on the mechanically mixed sample, whereas none of pyrochlore phase was observed at the coated sample after
thermal etching. Those different behaviors caused by the degree of homogeneous distribution of the additives in BaTiO3 matrix were confirmed by EDS analysis. 相似文献
10.
The Sr1-xCexMnO1- system (0 x 0.5) was investigated with respect to its structural, thermal and electrical properties. Although un-doped SrMnO3 has the perovskite structure above 1400°C, the structure is unstable at room temperature. However, partial substitution of Ce for Sr in SrMnO3 stabilizes the perovskite structure down to room temperature. Single phase perovskite is obtained for 0.1 x 0.3 in Sr1-xCexMnO1-, and it remains stable even following heat treatment at 800°C for 100 h. The dependence of the electrical conductivity on temperature was measured from room temperature to 1000°C in air. Ce doping dramatically enhanced the electrical conductivity of SrMnO3. Sr0.7Ce0.3MnO1- exhibits a higher conductivity (290 S · cm-1 at 1000°C) than that of La0.8Sr0.2MnO3 (LSM, about 175 S · cm-1) and remains n-type over the whole range of temperature examined. The thermal expansion coefficients in the system were nearly constant with values ranging between 1.24 × 10-6 and 1.01 × 10-6 cm/cm · K for temperatures of 50°C to 1000°C. 相似文献
11.
Abstract We have studied ferroelectric thin films deposited by sol-gel processing onto non-noble metal substrates. The results obtained indicate that by careful control of processing conditions, ferroelectric materials can be deposited onto these substrates, although interdiffusion between the metal and the ferroelectric can significantly degrade the ferroelectric properties of the materials. The effects of this interdiffusion are demonstrated and possible implications of ferroelectric-electrode interactions for fatigue in ferroelectric materials are discussed. 相似文献
12.
J. Hiltunen D. Seneviratne R. Sun M. Stolfi H. L. Tuller J. Lappalainen V. Lantto 《Journal of Electroceramics》2009,22(4):416-420
The crystallographic properties of BaTiO3 thin films, grown by pulsed laser deposition on MgO substrates, were found to be strongly influenced by the oxygen pressure
used during growth. Low pressure grown films were c-oriented while increasing oxygen pressure produced films with preferred
a-orientation. The crystal reorientation resulted in the shift of optical birefringence from +0.04 to −0.025 with low levels
of birefringence in films possessing low tetragonal distortion. Mach-Zehnder electro-optic waveguide modulators were fabricated
to characterize the electro-optic properties of the deposited films and to evaluate the suitability of these films for planar
optical applications. An effective electro-optic coefficient of 23 pm/V was obtained for a c-axis oriented film near the crystal c→a reorientation point. 相似文献
13.
The structural features of nanoscale BaTiO3 powders prepared by hydro-thermal techniques were investigated as a function of synthesis temperature. It was found that
the relative volume fraction of the cubic and tetragonal phases in the powders was sensitive to the synthesis conditions.
In particular, the variation in the lattice spacing with the depth from the surface of the powders prepared at 180∘C was measured. It’s highly likely that the surface region of the powders is of the tetragonal phase, while their cores are
of the cubic phase. A boundary between these two phases is located ∼ 5 nm from the powder surface. 相似文献
14.
Anton V. Polotai Tae-Hee Jeong Gai-Ying Yang Elizabeth C. Dickey Clive A. Randall Pascal Pinceloup Abhijit S. Gurav 《Journal of Electroceramics》2007,18(3-4):261-268
Microstructural control in thin-layer multilayer ceramic capacitors (MLCC) is one of the present day challenges to maintain
an increase in capacitive volumetric efficiency. This present paper opens a series of investigations aimed to engineer the
stability of ultra-thin Ni electrodes in BaTiO3-based multilayer capacitors using refractory metal additions to Ni. Here, pure Ni and Ni–1 wt.% Cr alloy powders are used
to produce 0805-type BME MLCCs with 300 active layers and with dielectric and electrode layer thickness around 1 μm. To investigate
the continuity of Ni electrodes, both MLCC chips with pure and doped electrodes were sintered at different temperatures for
5 h. It is found that the continuity of Ni electrodes is improved most likely due to the effect of Cr on the low-melting point
(Ni,Ba,Ti) interfacial alloy layer formation. The interfacial alloy layer is not observed when Cr is segregated at Ni-BaTiO3 interface in the Cr-doped samples, while it is found in all undoped samples. The interfacial alloy layer is believed to increase
mass-transfer along the Ni-BaTiO3 interfaces facilitating an acceleration of Ni electrodes discontinuities. 相似文献
15.
The effects of Mn-doping on TSDC (Thermally Stimulated Depolarization Current) and electrical degradation of BaTiO3 have been investigated. TSDCs of un-doped BaTiO3 and Ba(Ti1−x
Mnx)O3−δ exhibited the three sharp TSDC peaks around phase transition temperatures. TSDC of Ba(Ti0.995Mg0.005)O2.995 increased gradually from 50∘C and this anomalous depolarization current kept going up well above the Curie temperature (∼130∘C). TSDCs of un-doped BaTiO3 and Ba(Ti0.995Mn0.005)O3−δ decreased in the temperature range above the Curie point, whereas a slight increase in TSDC was confirmed at the specimen
of Ba(Ti0.99Mn0.01)O3−δ. TSDCs of Ba(Ti0.995−y
Mg0.005Mny)O3−δ (y = 0.005, 0.01) were lower than that of Ba(Ti0.995Mg0.005)O2.995. 相似文献
16.
Anton V. Polotai Tae-Hee Jeong Gai-Ying Yang Elizabeth C. Dickey Clive A. Randall Pascal Pinceloup Abhijit S. Gurav 《Journal of Electroceramics》2009,23(1):6-12
Multilayer ceramic capacitors based on BaTiO3 dielectric compositions and Ni inner electrodes have complex interfacial reactions that impact the continuity of the inner
electrode microstructure. Previously we demonstrated that through the addition of Cr to Ni, a significant improvement in the
continuity of ultra-thin Ni electrodes in Ni–BaTiO3 multilayer capacitors could be achieved. Here, the effect of the Cr addition to the nickel electrode pastes is studied with
regard to the electrical properties. Low-field electrical measurements demonstrate no major differences between Cr doped Ni
and undoped Ni. However, high-field measurements show a significant decrease to the total capacitor resistance. Under a critical
electrical bias the conductivity significantly increases due to a Fowler–Nordheim tunneling conduction though the interfacial
Schottky barrier at the dielectric–electrode interface; the onset voltage of this conduction is much lower than with the undoped
nickel. Based on these results, we evaluate criteria for the selection of an appropriate refractory metal in order to improve
the Ni electrode continuity. 相似文献
17.
Electrical conductivity, thermoelectric power, and chemical diffusivity are the most typical, charge-and-mass transport properties of a mixed ionic electronic conductor oxide which are essentially governed by its defect structure, and the oxygen nonstoichiometry is a direct measure of its overall defect concentration. For the system of BaTiO3–, the total electrical conductivity has been the most extensively and systematically studied as a function of oxygen partial pressure at elevated temperatures. The other properties have also been studied, but much less extensively and systematically. The electrical conductivity and thermopower were occasionally measured together on the same specimens so that mutual compatibility or consistency might be secured. But, the rest were all determined separately on the specimens of differing quality, consequently lacking in mutual consistency. It, thus, has remained hard to evaluate the canonical, defect-chemical parameters which are consistent with each and every of these defect structure-sensitive properties that were observed. Very recently the authors have determined the total conductivity, chemical diffusivity and thermoelectric power altogether on the same specimens of BaTiO3–, and the nonstoichiometry on the same-quality specimens at temperatures of 1073 T/K 1373 over wide enough a range of oxygen partial pressure (normally, 10–16 Po2/atm 1) that encloses an electron/hole/ion mixed regime. In this article, we will compile all the literature data on these defect-structure-sensitive properties and extract from the authors' own, without using any ad hoc assumptions regarding, e.g., the electronic carrier mobilities and effective density of states, the basic defect-chemical parameters including defect-equilibrium constants, carrier mobilities and densities, and electronic heats of transport, which are the most consistent with the properties observed. Compared to the conventional picture of the defect structure of undoped BaTiO3, thus, some new insights into the defect chemical nature of BaTiO3– are provided. 相似文献
18.
Barium titanate powder has been prepared via a semi-oxalate method that uses barium oxalate and TiO2 precursors, instead of titanyl oxalate. Barium oxalate was precipitated from nitrate solution onto the surface of TiO2 powders. Crystallization of BaTiO3 from the precursors was investigated by TGA, DTA and XRD analysis. It is evident that an intermediate barium oxycarbonate along with BaCO3, forms between 450–500°C and that decomposes to BaCO3 again at high temperature. Decomposition of BaCO3 occurs at much lower temperature, from 600°C onwards, due to the presence of TiO2. The precursor completely transforms into BaTiO3 at 900°C. Nanometer size BaTiO3 crystallites are produced during this synthesis due to the lower calcination temperature. The crystalline morphology of BaTiO3 is controlled mainly by the morphology of BaCO3, which formed in the intermediate stage. 相似文献
19.
Xinhua Zhu Qiming Hang Zhenjie Tang Zhibiao Xing Ye Song Jianmin Zhu 《Integrated ferroelectrics》2013,141(1):178-183
Microstructures of BaTiO3 (BT) nanoparticles synthesized by hydrothermal process, were investigated by transmission electron microscopy (TEM) and Raman spectra. TEM images showed that BT nanoparticles synthesized at high Ba/Ti molar ratios in the precursors had large particle sizes and cubic morphology. Small faceted-particles were observed in the BT powders synthesized by using ethylene glycol (EG) as solvent, in comparison to reactive medium of pure water or water-EG mixed solution. X-ray diffraction and selected area electron diffraction revealed that the as-produced BT nanoparticles exhibited a room temperature-stabilized cubic structure, whereas Raman spectra indicated a tetragonal phase BT existing in the produced nanoparticles, which is not the dominant phase due to the weak characteristic peak of tetragonal structure at 305 cm?1. HRTEM images demonstrated that the BT nanoparticles with either cubic or rectangular shapes, were bounded by their {100} facets, and a terrace-ledge-kink surface structure was frequently observed at the edges of rough nanoparticles. Surface steps lying on the {100} planes were clearly observed. However, in the spherical nanoparticles, their surface edges were very smooth, and no surface steps were observed. 相似文献
20.
The Y5V-1206 base-metal electrode (BME) multilayer ceramic capacitor (MLCC) chips have been characterised for crystalline
phases using X-ray diffractometry (XRD), and microstructure using optical microscopy (OM), scanning electron microscopy (SEM)
and transmission electron microscopy (TEM). The microstructure features found in the Ni electrode and the BaTiO3 dielectric layer are discussed in terms of the tensile backstresses induced upon firing due to constrained sintering heterogeneously.
The chemical compositions containing BaO-excess and additives CaO and ZrO2, determined for BaTiO3 grains by energy-dispersive spectroscopy (EDS) equipped in the TEM are also reported. However, no rare-earth oxides were
found in the grains. The representative microstructure of BaTiO3 grains containing dislocations is the “solid-solution” type distinctive from the “core-shell” of the X7R compositions. The
fact that no ferroelectric domains were detected suggests that the BaTiO3 grains are pseudo-cubic with the c/a ratio ≈ 1.0. 相似文献