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1.
Equilibrium electrical conductivity data for large-grained, poly crystalline, undoped BaTiO3 , as a function of temperature, 750° to 1000°C, and oxygen partial pressure, 10−20 < P O2 <10−1 MPa, were quantitatively fit to a defect model involving only doubly ionized oxygen vacancies, electrons, holes, and accidental acceptor impurities. The latter are invariably present in sufficient excess to control the defect concentrations through the compensating oxygen vacancies, except under the most severely reducing conditions. Singly ionized oxygen vacancies play no discernible role in the defect chemistry of BaTiO3 within this experimental range. The derived accidental acceptor content has a slight temperature dependence which may reflect some small amount of defect association. Deviation of the conductivity minima from the ideal shape yields a small P O2 -independent conductivity contribution, which is tentatively identified as oxygen vacancy conduction. 相似文献
2.
The defect structure of acceptor-doped (Fe, Al, Cr) polycrystalline strontium titanate was investigated by measuring the equilibrium electrical conductivity as a function of oxygen activity (10−21 ≤ao2 ≤1) and temperature (85°C≤ T ≤ 1050°C). The electrical conductivity was n type with ∼−1/4 dependence on a 02 for a02 <10−10 . For a02 >10−8 , the observed data for Fe- or Al-doped samples were proportional to ∼1/4.5 power of a02 . In this region for Cr-doped samples, the value of m in.σp αa02 +1/m varies from ∼4.80 to ∼9.00 as the concentration of Cr is increased from 460 to 10 000 ppm. The onset of p -type conductivity depends on the amount. of acceptor impurity added to the sample. The absolute values of the conductivity in the acceptor-doped samples were lower in the n-type region than those for undoped SrTiO3 . The conductivity minima shift toward lower oxygen activity with increasing acceptor concentration. For the entire oxygen activity rangae used in this study, the defect structure of SrTiO3 is dominated by the added acceptor impurities. 相似文献
3.
The electrical conductivity and thermoelectric power of single-crystalline Ba0.03 Sr0.97 TiO3 were measured over a wide temperature (800° to 1100°C) and oxygen partial pressure (105 to 10-15 Pa) range. Our experimental data, like those of previous workers on nominally undoped BaTiO3 or SrTiO3 , support a defect model based on doubly ionized oxygen vacancies, electrons, holes, and accidental acceptor impurities. The simultaneous measurement of electrical conductivity and thermoelectric power, together with precise experimental data obtained with an advanced thermoectric power measurement technique, enabled us to determine for the first time reliable values for the preexponential factors and the activation energies which characterize the defect equilibrium constants. These calculated values, together with the defect model, were found to give an excellent fit to the experimental data, and were used to generate the boundaries, in P o2 -1/ T space, of the various defect regimes. 相似文献
4.
The effect of added Al, as an acceptor impurity, on the equilibrium electrical conductivity of large-grained, polycrystalline BaTiO3 , is consistent with a previously proposed defect model which involves only doubly ionized oxygen vacancies, electrons, holes, and acceptor impurities. The behavior is an extension of that of undoped BaTiO3 , in which an accidental net acceptor excess already plays an important role. Comparison of the derived active acceptor content with the amount of added Al indicates that Al is <50% effective in creating acceptor levels. The magnitude of a small Po2 -independent conductivity component, necessary to fit the observed conductivity minima, increases with added Al content. This is consistent with a contribution from extrinsic oxygen vacancy conduction. 相似文献
5.
R. WASER 《Journal of the American Ceramic Society》1988,71(1):58-63
Thermal desorption studies and electrical conductivity measurements have been used to investigate the solubility of hydrogen defects in barium titanate ceramics in oxidizing atmospheres. Hydrogen is found to dissolve in the perovskite lattice of undoped and acceptor-doped BaTiO3 by the formation of hydroxide ions on regular oxygen ion sites. The hydrogen defects act as mobile donors and may substitute the oxygen vacancies in compensating fixed acceptors. From the dependence of the solubility on the water vapor pressure and the dopant concentration, the incorporation/desorption equilibrium reaction is deduced. A defect model is derived which consistently extends previously proposed models. The influence of Ba2 TiO4 and Ba6 Ti17 O40 second phases on the solubility of hydrogen defects is discussed. 相似文献
6.
YOUNG HO HAN JOHN B. APPLEBY DONALD M. SMYTH 《Journal of the American Ceramic Society》1987,70(2):96-100
The equilibrium electrical conductivity of polycrystalline, calcium-doped BaTiO3 was studied over the oxygen partial pressure range 10-13 to 105 Pa and the temperature range 800° to 1000°C. There is little effect if CaO is substituted for a corresponding amount of BaO, i.e., Ba, 1-x Cax TiO3 . If CaO is substituted for a corresponding amount of the TiO2 content, i.e., BaTi1-x Cax O3-x , the equilibrium conductivity shows strong evidence of acceptor-doped behavior. If the corresponding amount of excess CaO is added to stoichiometric BaTiO3 , i.e., BaCax TiO3+x , the conductivity profiles are very close to those for samples with TiO2 replaced by CaO, and show highly acceptor-doped behavior. This is in agreement with the replacement of a small amount of Ti by Ca2+ on the octahedral B-sites of BaTiO3 , where it acts as an acceptor center, CaT 相似文献
7.
受主掺杂铅酸钡陶瓷的缺陷补偿机理 总被引:2,自引:1,他引:2
由非化学计量比引起的晶体缺陷是影响材料电学和光学性能的主要因素之一,而掺杂是造成材料非化学计量比的一个重要因素.在未掺杂铅酸钡(BaPbO3)缺陷化学研究的基础上,采用高温平衡电导法分析了铝(Al)受主掺杂BaPbO3的缺陷补偿机理,建立了受主掺杂BaPb03的缺陷化学模型.具体分析了受主杂质对材料高温平衡电导率、高氧分压和低氧分压下的主导缺陷转变点的影响.在高氧分压下,受主掺杂BaPbO3的缺陷行为由本征缺陷所控制,受主掺杂对平衡电导率的影响不大.随着氧分压的下降,材料由本征缺陷控制转变为非本征缺陷控制,受主掺杂可以提高平衡电导率.在高氧分压和低氧分压区域的主导缺陷转变点因受主杂质的存在而向高氧分压方向移动. 相似文献
8.
Bernhard Ostrick Maximilian Fleischer Hans Meixner 《Journal of the American Ceramic Society》1997,80(8):2153-2156
Simultaneous Hall and conductivity measurements were performed in situ between 650° and 1050°C on n-type semiconducting BaSnO3 ceramics. The variation of the Hall mobility and the Hall carrier density as a function of oxygen partial pressure between 102 and 105 Pa and of temperature was investigated. At temperatures below 900°C the conductivity exhibits a dependence on temperature and oxygen partial pressure which is mainly determined by variations of the Hall mobility. Above 900°C most of the significant dependence is due to a variation in carrier density. Furthermore, a simple defect model assuming doubly ionized oxygen vacancies and acceptor impurities is discussed for BaSnO3 . 相似文献
9.
Veerabhadrarao Bheemineni Edward K. Chang Misri Lal Martin P. Harmer Donald M. Smyth 《Journal of the American Ceramic Society》1994,77(12):3173-3176
The solubilities of acceptor impurities are strongly suppressed when BaTiO3 is densified in highly reducing atmospheres. This is evidenced by a shift in the minimum in the equilibrium electrical conductivity to higher oxygen activities, a decrease in the ionic contribution to the conductivity, and a decrease in the leakage current and the rate of leakage current degradation under temperature–voltage stress. The normal solubility is restored by subsequent anneals in air that result in substantial grain growth, and the properties then revert to those of BaTiO3 sintered in air. The solubility suppression is attributed to a mass-action interaction between the processes that generate oxygen vacancies, those that result from the compensation of acceptor centers, and those that result from reduction. 相似文献
10.
Space Charge Segregation at Grain Boundaries in Titanium Dioxide: I, Relationship between Lattice Defect Chemistry and Space Charge Potential 总被引:2,自引:0,他引:2
The electrical potential difference between the interface and the bulk in TiO2 is obtained as a function of temperature, oxygen pressure, and acceptor or donor doping from a space charge model that explicitly includes the high-temperature lattice defect chemistry. Using defect equilibrium constants for TiO2 from previous literature studies, it is shown that for a space charge determined by ionic defect equilibration with the interface, the potential is negative in undoped and acceptor-doped TiO2 and positive at high donor concentrations. The isoelectric point lies in the donor-doped regime at high temperatures due to the contribution of defects from reduction, even for fairly oxidizing ambients. 相似文献
11.
The oxygen vacancy concentration of BaTiO3 doped with acceptors (Cr to Ni) is determined gravimetrically as a function of the O2 partial pressure during and after annealing at 700° to 1300°C. The oxygen vacancy concentration of these materials is larger than that of undoped and donor-doped BaTiO3 . The oxygen vacancies are doubly ionized and they compensate the acceptors of lower valence. Both the vacancy concentration and the valence of the acceptor dopants depend on the annealing conditions. The electronic energy levels of the acceptors within the BaTiO3 band gap are derived from the gravimetric measurements. The electrical properties of the acceptor-doped ceramics are favorable for base-metal-electrode multilayer capacitors, which require sintering in reducing atmospheres. 相似文献
12.
TiO2 is observed as a second phase in SrTiO3 having Sr/Ti ≤ 0.995 (≥0.5 mol% excess TiO2 ). The effect of excess TiO2 on the equilibrium electrical conductivity at 1000°C is consistent with a solubility of <0.1 mol% TiO2 with the formation of unassociated oxygen vacancies. More Ti02 is retained in solid solution when samples are quenched from the sintering temperature rather than furnace-cooled. The effect of excess SrO on the equilibrium electrical conductivity also indicates some solid solubility. 相似文献
13.
The electrical conductivity and thermoelectric power of KTaO3 were measured from 900° to 1300°C over a range of oxygen partial pressures. The isothermal electrical conductivity showed a minimum at an oxygen partial pressure corresponding to the transition between p-type and n-type behavior. A point defect model was developed which involved fully ionized potassium and tantalum vacancies, singly and doubly ionized oxygen vacancies, holes, and electrons. The values of all pertinent equilibrium constants were calculated from the experimental data and the nonsimplified neutrality condition was solved to give each of the defect concentrations as a function of temperature and oxygen partial pressure. The calculated conductivity agreed extremely well with the experimental data over the full temperature and oxygen partial pressure range, and the band gap derived from these calculations (3.43 eV) was in excellent agreement with the reported value (3.5 eV). 相似文献
14.
The electrical conductivity of polycrystalline TiTa2 O7 was measured at 1000° and 1050°C as a function of oxygen partial pressure from 10−1 to 10−21 MPa. In the apparent n-type region, the value of m in σn ∝PO2 −1/m was found to be ∼6 in the region >10−17 MPa and ∼4from 10−16 to 10−9 MPa. The conductivity appeared to be p-type for P02 <10−5 MPa. The measured data are explained on the basis of the presence of small amounts of acceptor impurities in the undoped sample. 相似文献
15.
The defect structure of high-purity, polycrystalline HfO2 was investigated by measuring the oxygen partial pressure dependence of the electrical conductivity and the sample weight. From 1000° to 1500°C and above oxygen partial pressures of 10 −6 , the conductivity is electronic and proportional to p o2 1/5 . The predominant defect is completely ionized hafnium vacancies. At lower oxygen partial pressures a broad shallow minimum in the lower temperature conductivity isotherms indicates the presence of an oxygen pressure independent source of electronic charge carriers. By combining the weight change and conductivity data, mobility values were found to vary from 1.6 × 10−3 to 3 × 10−4 cm2 /V-sec. The activation energies for the hole mobilities were calculated to be 0.2 ev above 1300° C and 0.7 ev below this temperature. 相似文献
16.
Electrical conductivity, thermoelectric power, and weight change were measured for polycrystalline Ta2 O5 from 900° to 1400°C. The predominant ionic and electronic defects in this temperature range are oxygen vacancies and electrons. The oxygen-vacancy and electron mobilities are 8.1 × 103 exp (−1.8 eV/ k T) and ∼0.05 cm2 /V-s, respectively. At O2 partial pressures near 1 atm, the ionic-defect concentration is essentially fixed by the presence of lower-valence cation impurities, and the total electrical conductivity is predominantly ionic, whereas at low P o2 's the conductivity is electronic and proportional to P P o2 −1/6 . 相似文献
17.
未掺杂铅酸钡陶瓷的缺陷补偿机理 总被引:2,自引:1,他引:1
用高温平衡电导法研究了未掺杂铅酸钡(BaPbO3)陶瓷的缺陷化学,确定了未掺杂BaPbO3材料的缺陷化学模型,同时,从BaPbO3材料的缺陷结构的角度讨论了热处理气氛对材料室温电导率的影响.BaPbO3材料在实验氧分压范围内呈现p型电导,在高氧分压下,铅离子(Pb4 )空位和空穴占主导,材料表现出本征缺陷行为.在中氧分压下,受主杂质成为主导缺陷,电荷补偿缺陷为空穴.在低氧分压下,受主杂质的电荷补偿缺陷转变为氧离子空位,还原反应成为电荷补偿缺陷的主要来源.材料室温电导率的变化完全是由于在不同的氧分压环境下材料中主导缺陷的转变和缺陷浓度的变化而引起的. 相似文献
18.
The defect structure of monoclinic ZrO2 was studied by measuring the transfer numbers and electrical conductivity as functions of O2 pressure and temperature. The data suggest a defect structure of doubly ionized oxygen vacancies at low pressures, i.e. <10−19 atm, and singly ionized oxygen interstitials at pressures >10−9 atm. Zirconia is primarily an ionic conductor below #700°C and an electronic conductor at 700° to 1000°C for 10−22 ≤Po2 ≤1 atm. 相似文献
19.
Maximilian Fleischer Hans Meixner Christian Tragut 《Journal of the American Ceramic Society》1992,75(6):1666-1668
The oxidation reaction equilibrium constant and the holes mobility in p -type-semiconducting SrTiO3 single crystals were determined directly by simultaneous Hall and conductivity measurements between 500° and 1000°C. This information and the SrTiO3 defect model were used to interpret the electrical measurements taken on this substance which represents a model substance for semiconducting perovskites. Measurements with varying oxygen partial pressures showed that shifts of the crystal defect equilibrium give rise to changes in the carrier concentration with unchanged carrier mobility. 相似文献
20.
Equilibrium electrical conductivity of nonstoichiometric poly-crystalline BaTiO3 with varying Ba:Ti ratios was investigated at temperatures between 800° and 1200°C and P o2 from 10−22 to I atm. A transition from p -type to n -type conductivity was observed. Although the electrical conductivity of different specimens varied slightly, these differences did not appear to be a function of the Ba:Ti ratio in the region investigated. An intrinsic band-gap energy of ∼3.1 eV was calculated from the temperature dependence of the minimum conductivity. The O2 partial pressure dependence of the isothermal n -type conductivity cannot be described by simple defect models incorporating only singly or doubly ionized O vacancies. Likewise, simple defect models incorporating cation vacancies are not consistent with the observed pressure dependence of the p -type conductivity. More complex defect models which correspond to the observed behavior over the entire range of temperature and P o2 will be discussed in a subsequent paper. 相似文献