Co-Doping Effect of Mn and Y on Charge and Mass Transport Properties of BaTiO3

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^{– 6}at 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.     

Effects of Mn-doping on TSDC and degradation of BaTiO3

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(Ti_1−x Mn_x)O_3−δ exhibited the three sharp TSDC peaks around phase transition temperatures. TSDC of Ba(Ti_0.995Mg_0.005)O_2.995 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(Ti_0.995Mn_0.005)O_3−δ decreased in the temperature range above the Curie point, whereas a slight increase in TSDC was confirmed at the specimen of Ba(Ti_0.99Mn_0.01)O_3−δ. TSDCs of Ba(Ti_0.995−y Mg_0.005Mn_y)O_3−δ (y = 0.005, 0.01) were lower than that of Ba(Ti_0.995Mg_0.005)O_2.995.     

Study of the Electrical Properties of Pb(Mg,Ni)1/3Nb2/3O3-PbTiO3 System Across the Morphotropic Phase Boundary

Phase transitional behavior and electrical properties of (1 – x)Pb(Mg,Ni)_1/3Nb_2/3O₃-xPbTiO₃ ceramics (PMNN-PT with Mg/Ni = 1:1, x = 0.20–0.40) across the morphotropic phase boundary (MPB) were examined. X-ray diffraction and dielectric measurement reveal that two phases, pseudocubic and tetragonal phases, coexist in the composition range x = 0.30–0.36. The maximum d ₃₃ (about 570 pC/N) was observed at the composition x = 0.32–0.34. Dielectric and ferroelectric properties exhibit abnormal high near the MPB. An unusual peak shoulder occurred in the dielectric measurement upon thermal cycling for poled samples. This phenomenon was considered to be associated with the macro to micro domain transition and depolarization.     

Microwave Dielectric Properties of Ferroelectric BaTiO3 Thin Film

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.     

Protonic Conduction in SrY0.5Ta0.5O3-Based Ceramics at Elevated Temperatures

The perovskite-type-oxide solid solution SrY_0.5+x Ta_0.5+x O_3– was synthesized and its properties were investigated. The single phase character of the samples was confirmed by X-ray diffraction when 0 x 0.02, while lines from the impurity phase SrY₂O₄ appeared in patterns of x 0.03. The conductivities of SrY_0.52Ta_0.48O_3– were about an order of magnitude higher than those of SrY_0.50Ta_0.50O₃. The results of electrochemical measurements such as emf measurements of gas concentration cells, isotope effect in conductivity, and oxygen partial pressure dependence of conductivity showed that SrY_0.52Ta_0.48O_3– exhibited pure protonic conduction in reducing atmospheres and p-type electronic conduction under high oxygen partial pressure conditions.     

Electrical Properties of 6H-BaTi0.95M0.05O3−δ Ceramics where M = Mn, Fe, Co and Ni

Hexagonal BaTiO₃ materials have been stabilised at room temperature according to the formula BaTi_0.95M_0.05 O_3– where M = Mn, Fe, Co and Ni. Dense ceramics (> 96% of the theoretical X-ray density) were sintered at 1450C in flowing O₂ gas from calcined powders prepared by the mixed oxide route at 1300C. All samples were single-phase and the bulk conductivity, _b, measured by Impedance Spectroscopy and Q.f measured by microwave dielectric resonance methods showed a strong dependence on the type of dopant. _b at 300C was 10^–7, 10^–5.5, 10^–5.5 and 10^–4 Scm^–1 for M = Mn, Fe, Ni and Co, respectively and Q.f at 5 GHz was 7790, 6670, 2442 and 1291 GHz, for M = Mn, Fe, Ni and Co, respectively. The correlation between _b and Q.f is attributed to the presence of oxygen vacancies and/or mixed valency of the dopant ions.     

Synthesis, Physicochemical Characterization and Ionic Conductivity of LaGa0.4Mg0.2M0.4O3−δ (M = Cr, Mn, Fe, Co)

Partial electronic and ionic conductivities, crystal structure, thermal expansion and infrared absorption spectra of the perovskite-type series, LaGa_0.40Mg_0.20M_0.40O_3– (M = Cr, Mn, Fe, and Co), have been studied. The rhombohedral distortion of the perovskite lattice decreases and the unit cell volume increases in the sequence Co < Cr < Mn < Fe. The p-type electronic conduction increases with atomic number of the transition metal cation; the activation energy varies in air from 15.9 to 32.1 kJ/mol. The oxygen ionic conductivity of the M-doped phases at temperatures below 1200 K is significantly lower than that of LaGa(Mg)O₃. The highest ionic conductivity was found for the Fe- and Co-containing phases. The ion transference numbers of La(Ga,Mg,M)O_3– at 970–1270 K were determined to vary in a wide range, from 2 × 10^–5 to 3 × 10^–2. Thermal expansion coefficients, calculated from the dilatometric data collected in the temperature range 300–1100 K, lie in the range (7.2–15.5) × 10^–6 K^–1.     

Characterization of Pr- and Sm-Doped Ce0.8Gd0.2O2 − δ

Ce_0.8Gd_{0.2 – y}Pr_yO_{2 –} (y = 0–0.05) and Ce_0.8Gd_{0.2 – y}Sm_yO_{2 –} (y = 0–0.05) SOFC electrolyte materials were prepared using a reverse-strike co-precipitation method. The resulting powders were characterized using X-ray diffraction, Raman spectroscopy and electrochemical methods. XRD confirmed a single fluorite phase for all compositions. Increased Pr and Sm dopant level was found to cause a shift in the peak positions to slightly higher d-spacings with respect to pure CeO₂. The experimental lattice parameter was calculated using the peak positions determined from the XRD patterns. Raman spectra, for all dopant levels, showed two distinctive band features, namely a band at ca. 460 cm^{– 1} and a broader, weaker band at ca. 570 cm^{– 1}. As the proportion of praseodymia dopant is increased, the oxygen vacancy band shifts to a slightly lower wavenumber and decreases in relative intensity to the F_2g band. However, an anomaly occurs at the 1% dopant level; the oxygen vacancy band having a very low relative intensity. The conductivity was determined using AC—impedance spectroscopy, and it was found that for praseodymia, a maximum is observed at y = 0.015, while for samaria the maximum is observed at y = 0.01. It is also observed that the ionic conductivity for the samaria doped samples are lower than those of the praseodymia doped samples.     

Investigation of Semiconducting Barium Titanate Ceramics by Oxygen Coulometry

Donor-doped BaTiO₃ ceramics (0–0.6 mol% Nb) were investigated during the sintering process at an oxygen partial pressure of 2.4 Pa and at a maximum temperature of 1430C. The occurring oxygen exchange with the ambient atmosphere was monitored quantitatively by oxygen coulometry. The coincidence between the grain growth behavior and the occurrence of distinct oxygen release peaks during the anomalous grain growth reveals that significant amounts of the donor are incorporated and charge-compensated by electrons only under the conditions of the anomalous grain growth. Quantitative analysis of the coulometric data shows that at a doping level of 0.2 mol% nearly all donors are charge-compensated by electrons. With increasing Nb concentration also Ti vacancies gradually begin to serve for compensation. At 0.5 mol% Nb their influence reaches 70 % of the electronic compensation.     

Partial Electronic Conductivity and Chemical Diffusivity of Li<Subscript>3<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript>2/3−<Emphasis Type="Italic">x</Emphasis></Subscript>TiO<Subscript>3</Subscript> Solid Solution

Partial electronic conductivity and chemical diffusivity of Li have been measured on the system of Li_3xLa_2/3–xTiO₃ (LLT) with x = 0.13, a prospective Li⁺ electrolyte, against oxygen activity in the range of 10^–22 < a_O2 < 0.21 at 557, 610 and 663C, respectively by an ion-blocking polarization technique. It is found that the electronic conductivity of LLT, which in air is essentially an ionic conductor, varies as a_O2^–1/4 to render it mixed-conductive in reducing atmospheres, say, in a_O2 < 10^–12. The chemical diffusivity of component Li also increases from a value of the order of 10^–8 cm²/s in air atmosphere up to a maximum on the order of 10^–3 cm²/s as the electronic conductivity increases with decreasing oxygen activity. This is attributed to the variation of the electronic transference number and the thermodynamic factor with oxygen activity. The latter has been evaluated to be on the order of 10–10³.     

Dielectric Properties of Bi4−x La x Ti3O12 (0 ≤ x ≤ 2) Ceramics

The dielectric properties of the Bi_4–x La _x Ti₃O₁₂ (0 x 2) ceramics were characterized and discussed together with the P-E relation (polarization vs. electric field). With increasing x, the P-E relation changed from normal ferroelectric hysteresis loops to pure linear relation, which indicated that La³⁺ substitution for Bi³⁺ in Bi₄Ti₃O₁₂ induced a phase transition from ferroelectric to paraelectric state at ambient temperature. Low loss dielectric ceramics with temperature stable dielectric constant were obtained for x > 1.2 in Bi_4–x La _x Ti₃O₁₂ at 1 MHz. And the loss increased in all the compositions when the ceramics were measured at microwave frequencies.     

Characteristics of Textured Ce-Zr Mixed-Oxide Films as Buffer Layer for YBCO Coated Conductors

Single- and multi-layer (Ce_{1 – x} Zr _x )O₂ films (0 x 0.84) on Si (100) and polycrystalline Ni substrates were prepared using RF and DC magnetron co-sputtering. XRD of scan analysis showed that all (Ce_{1 – x} Zr _x )O₂ films were biaxially oriented with the c-axis perpendicular to the plane of the film. During sputtering, DC power to the Zr target was fixed at 200 W, while RF power to the Ce target was set at 30 W, 50 W, or 100 W. As-deposited ZrO₂ film was amorphous and was crystallized by post-annealing. However, as-deposited (Ce_{1 – x} Zr _x )O₂ films were crystalline even when grown at room temperature and the structures of films were cubic or tetragonal depending on the Ce ion incorporation. It was found that multilayered CeO₂/(Ce_{1 – x} Zr _x )O₂/CeO₂ films could be deposited with a continuous compositional gradient in a sputtering batch. This layered CeO₂/CZO/CeO₂ structure can maintain its original texture after 800°C annealing and is therefore suitable for subsequent YBCO film growth. Furthermore, Ni diffusion is effectively blocked by the buffer layers just like the YSZ currently used in coated conductor fabrication.     

Hydrothermal Preparation and Characterization of Ultra-Fine BaTiO3 Powders from Amorphous Peroxo-Hydroxide Precursor

Ultra-fine BaTiO₃ powders were hydrothermally prepared by using Ba Ti-peroxo-hydroxide precursor. Amorphous Ba Ti-peroxo-hydroxide precursor were prepared by coprecipitation of Ba(NO₃)₂ and TiCl₄ aqueous solution adding in NH₄OH aqueous solution. The phase-pure BaTiO₃ powders with a cubic perovskite structure were synthesized at temperature as low as 110_C and in the pH range of 10–12. This processing method provides a simple low temperature route for producing BaTiO₃ nanoparticles. Under a TEM image and a SAD pattern analysis, it is evident that BaTiO₃ powders had spherical shape and single crystal nature. The BaTiO₃ ceramic sintered at 1200_C for 1 h had 97% of theoretical density and a relatively high dielectric constant ( _r = 3500).     

Dielectric and Piezoelectric Properties of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-K<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript>-NaNbO<Subscript>3</Subscript>Lead-Free Ceramics

The ternary lead-free piezoelectric ceramics system of (1 – x) [0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃] – xNaNbO₃(x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized by conventional solid state reaction method. The crystal structure, dielectric, piezoelectric properties and P-E hysteresis loops were investigated. The crystalline structure of all compositions is mono-perovskite phase ascertained by XRD, and the lattice constant was calculated from the XRD data. Temperature dependence of dielectric constant _r and dissipation factor tan measurement revealed that all compositions experienced two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric, and these two phase transitions have relaxor characteristics. Both transition temperatures T_d and T_m are lowered due to introduction of NaNbO₃. P-E hysteresis loops show that 0.88Na_0.5Bi_0.5TiO₃-0.12K_0.5Bi_0.5TiO₃ ceramics has the maximum P_r and E_c corresponding to the maximum values of electromechanical coupling factor K_p and piezoelectric constant d_33. The piezoelectric constant d₃₃ and electromechanical coupling factor K_p decrease a little, while the dielectric constant ₃₃^T/₀ improves much more when the concentration of NaNbO₃ is 8 mol%.     

Scaling Effect on the Dielectric Constant in Ba(Ti x Zr1−x )O3 Thin Films

Recent work on PZT and BST thin films reveal a thickness dependence of the dielectric constant for a film thickness below 100 nm. This effect is commonly attributed to an interfacial layer between the electrode and the dielectric film (dead layer). In this contribution we report on the influence of the film thickness on the dielectric constant of Ba(Ti_xZr_{1 – x})O₃ thin films with different Zr-contents (x = 0–30 at.%). The films were prepared by chemical solution deposition (CSD) with thickness between 30 and 350 nm.The electrical characterization was performed in a temperature range between 25 and 200C. Results were interpreted with respect to the formation of a serial dead layer capacitance.     

Dielectric Properties and Sintering Characteristics of CaTiO<Subscript>3</Subscript>-(Li<Subscript>1/2</Subscript>Nd<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript> Ceramics

The dielectric properties and the sintering effect upon microstructure of (1–x) CaTiO₃-x(Li_1/2Nd_1/2)-TiO₃ Ceramics are investigated in this paper. Nd³⁺ and Mg^{2 +} ions co-substitution for Ca^{2 +} on A site improves the sintering characteristic of CaTiO₃ ceramics with forming orthorhombic perovskite structure. The structure of (1 – x) CaTiO₃-x(Li_1/2Nd_1/2)TiO₃ changes from orthorhombic to tetragonal as (Li_1/2Nd_1/2)TiO₃ addition increasing. Limited solubility of (Li_1/2Nd_1/2)TiO₃ in CaTiO₃ forming a part solid solution compound achieves the adjustment of for CaTiO₃ at low sintering temperature. The proper dielectric properties with = 78, tan = 0.0006, = +7 ppm/C are obtained for 0.8Ca_0.67(Nd,Mg)_0.22TiO₃-0.2(Li_1/2Nd_1/2)TiO₃ ceramics.     

Synthesis, Microstructure and Electrical Properties of Hydrothermally Prepared Ferroelectric BaTiO3 Thin Films

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 TiO_x 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.     

Mn-doped BaTiO3: Electrical Transport Properties in Equilibrium State

The electrical conductivity and thermoelectric power of Mn-doped BaTiO₃ (1 mole%) and undoped BaTiO₃ have been measured as functions of oxygen partial pressure (in the range of 10^-16 to 1 atm) and temperatures (in the range of 900 to 1200°C), and compared with each other to differentiate the effect of the Mn-addition. It is found that the isothermal conductivity of Mn-doped BaTiO₃ varies with increasing Po₂ as to to , unlike previously reported. This behavior is well explained by the shift of the ionization equilibrium, . The corresponding equilibrium constant, K_A, is determined from the Po₂ values demarcating those three different Po₂ regions as =3.19×10²² exp(–1.69 eV/kT). Basic parameters involving carrier density and mobility, and defect structure of Mn-doped BaTiO₃ are discussed in comparison with those of undoped BaTiO₃.     

Crystal Growth and Dielectric Properties of New Ferroelectric Barium Titanate: BaTi2O5

Single crystals of the ferroelectric BaTi₂O₅ and BaTiO₃ were prepared from a solution of 33-mol% BaO and 67-mol% TiO₂ by a rapid cooling method. The dielectric constant () and dielectric loss tangent (tan) were measured in a wide temperature range of 10–860 K and in a frequency range of 0.1–3,000 kHz. The along the b-axis of the BaTi₂O₅ crystal, prepared in air, shows a sharp dielectric anomaly reaching 30,000 at the ferroelectric Curie temperature of T_C = 752 K. By contrast, the crystal prepared in a reducing atmosphere shows a diffuse phase transition near T_C = 703 K. The values of and tan are compared between these three crystals consisting of two kinds of BaTi₂O₅ and one BaTiO₃.     

BaTiO3−δ: Defect Structure, Electrical Conductivity, Chemical Diffusivity, Thermoelectric Power, and Oxygen Nonstoichiometry

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 BaTiO_3–, 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 BaTiO_3–, 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 BaTiO_3– are provided.