Influence of vanadium substitution on the conductivity of Bi3.25La0.75Ti3O12 and Bi3.25La0.75Ti2.97V0.03O12 ceramics

We have fabricated Bi_3.25La_0.75Ti₃O₁₂ and Bi_3.25La_0.75Ti_2.97V_0.03O₁₂ ceramics using the conventional solid-state reaction method. We measured their dc conductivity and analyzed the impedance spectroscopy in order to clarify the influence of vanadium substitution for titanium site on Bi_3.25La_0.75Ti₃O₁₂ ceramic. The vanadium substitution for titanium site in Bi_3.25La_0.75Ti₃O₁₂ can reduce the Bi cation and oxygen vacancies. Furthermore, the elimination of these defects, trapped in the grain boundary and grain-electrode interface, significantly reduces the influence of domain pinning, which would be responsible for the improvement in the ferroelectricity and piezoelectricity.     

Structural and Electrical Properties of Bi 3.25 La 0.75 Ti 3 O 12 and Bi 3.25 Pr 0.75 Ti 3 O 12 Thin Films for Memory Applications

In this work, Bi 3.25 La 0.75 Ti 3 O 12 (BLT) and Bi 3.25 Pr 0.75 Ti 3 O 12 (BPT) thin films were prepared by chemical solution deposition and characterized by X-ray diffraction, scanning electron microscope and electrical measurements. Layered perovskite BLT and BPT films can be achieved by 180 s annealing at a temperature as low as 650 C. Both BPT and BLT films are composed of closely packed spherical grains. BPT shows larger remnant polarization ( Pr ) and smaller coercive field. The Pr values of 700 C annealed BLT and BPT films are 18.3 w C/cm 2 and 20.5 w C/cm 2 , respectively, while BLT films show better-saturated hysteresis loops. The leakage current density of BPT films is significantly (about one order) lower than that of BLT. The dielectric properties of BLT and BPT films were measured and compared. Both films exhibit large dielectric constant and small loss tangent. Under bipolar switching cycles, BLT films showed little polarization reduction but a 30% polarization loss was observed for BPT films after 2 2 10 9 cycles.     

Effect of vanadium doping on ferroelectric and electrical properties of Bi3.25La0.75Ti3O12 thin film

Bi_3.25La_0.75Ti₃O₁₂ (BLT) and V-doped BLT (BLTV) thin films were prepared on Pt/Ti/SiO₂/Si substrates by a pulsed laser deposition method. The effects of V doping on ferroelectric and electrical properties were investigated by polarization-electric field hysteresis loops and leakage current-voltage measurements. BLTV single phases were confirmed by X-ray diffraction. Remnant polarization was increased and the leakage current density was decreased by V doping. The leakage current density of BLT thin films suddenly increased at 100 kV/cm while that of BLTV thin films increased at the higher electric field of 160 kV/cm. The power law relationship J α Eⁿ of current density vs. applied electric field is estimated to be J αE^2.0 for BLT and J αE^1.0 for BLTV thin films. The leakage current of the BLT/Pt junction can be explained by space-charge-limited current. However, that of the BLTV/Pt junction was characterized by the Schottky emission behavior.     

Conduction mechanism of grain oriented Bi3.15Nd0.85Ti3O12 ceramics fabricated by a hot-forging method

We have fabricated ordinary fired (OF) and grain oriented Bi_3.15Nd_0.85Ti₃O₁₂ (HF[⊥], HF[//]) samples by a hot-forging technique. The grain orientation factor F calculated from X-ray diffraction patterns of the c-axis oriented Bi_3.15Nd_0.85Ti₃O₁₂-HF[//] sample is determined to be above 90%. The dielectric and ferroelectric properties of Bi_3.15Nd_0.85Ti₃O₁₂ ceramics with different grain orientation have been investigated as a function of temperature. The a-b axis oriented Bi_3.15Nd_0.85Ti₃O₁₂-HF[⊥] sample had an enhanced dielectric constant (1163 at T _c) and ferroelectric properties (P _r ∼ 32 μC/cm²). The electrical conductivity of BNT ceramic has been studied as a function of temperature in order to investigate the conduction mechanism with different grain orientations.     

Sol-gel法制备Bi3.25La0.75Ti2.94Nb0.06O12铁电薄膜及其性能研究

采用溶胶-凝胶法(Sol-gel)在p_Si和Pt/Ti/SiO2/Si衬底上制备Bi3.25La0.75Ti2.94Nb0.06O12(BLTN)铁电薄膜,研究了BLTN薄膜的晶相结构、表面形貌、铁电性能、介电性能和C_V性能。结果表明:所制备的BLTN薄膜具有单一的层状钙钛矿结构,且为随机取向;高于650℃退火处理的BLTN薄膜表面平整致密;铁电性能测试显示较饱和的电滞回线;当退火温度为650℃时,其剩余极化Pr和Ec分别为24.6μC/cm2和96.8 kV/cm,明显优于Bi3Ti4O12(BIT)薄膜的铁电性能;室温下,当测试频率为10 kHz时,薄膜的介电常数为386,介电损耗为0.69%,具有良好的介电性能;C_V曲线为顺时针方向回滞,记忆窗口约为1.5 V,可以实现极化存储。     

Microstructure development in textured BaBi4Ti4O15 made by templated grain growth method

The effect of template and matrix particle sizes on microstructure development was examined for BaBi₄Ti₄O₁₅ textured by the templated grain growth method. Microstructure development was characterized by (1) the shape change of matrix particles from equiaxed to platelike, which resulted in texture development in the matrix phase, and (2) the formation of groups of large platelike grains with parallel alignment. The template particle size determined the size of grains in the final microstructure which was formed by process (2), and the matrix particle size influenced the rate of process (1).     

Structure dependence of the ferroelectric properties of Bi3.25Ln0.75Ti3O12 (Ln=La, Nd, Sm, Dy) ceramics

We have fabricated rare-earth ion substituted bismuth titanate (BIT) ceramics, Bi_3.25Ln_0.75Ti₃O₁₂ (BLnT; Ln=La, Nd, Sm, Dy), using the conventional solid-state reaction method and have investigated the changes in the structural distortion and electrical properties, which resulted from the substitution of the rare-earth ions in BIT ceramics. As the ionic radius of the rare-earth ion substituted into the BIT decreased, the structural distortion and decreases in the unit cell volume became more pronounced as well as the Curie temperature increased monotonically from 354 °C (BLaT) to 480 °C (BDyT). BNdT ceramics had relatively high remanent polarization value (12.5 μC/cm²) at an applied electric field of 130 kV/cm. The extent of the structural distortion influenced the dielectric and ferroelectric properties of the BLnT ceramics.     

Asymmetric capacitance-voltage characteristics of (Bi3.25, La0.75)Ti3O12 thin films grown on Si

Abstract

Electrical properties of Lamodified bismuth titanate Bi_3.25La_0.75Ti₃O₁₂) thin films for a metal-ferroelectric-insulator-semiconductor (MFIS) structure were investigated with capacitance-voltage (C-V). The MFIS structure exhibits progressively increasing C-V memory window with a sweep voltage due to ferroelectric polarization with suppressed charge injection. Moreover, the asymmetric shift of threshold voltage with a sweep voltage was observed. The flat-band voltage (V_fb2) at the negative sweep was gradually increased with a sweep voltage. The flatband voltage (V_fb1) at the positive sweep decreased at low sweep voltages and then increased at further high voltages (i.e., V_fb1 shift toward the positive direction rather than the negative direction). The asymmetric behavior of C-V characteristics was attributed to negative trapped charges by electron injection from Si.     

Ferroelectric Properties of Bi3.25Nd0.75Ti3O12 Thin Films Prepared by MOD Process

Ferroelectric Bi_{4 – x}Nd_xTi₃O₁₂(BNdT) thin films with the composition (x = 0.75) were prepared on Pt/Ti/SiO₂/Si(100) substrate by metal-organic deposition. The films were annealed by various temperatures from 550 to 650C and then the electrical and structural characteristics were investigated for the application of FRAM. Electrical properties such as dielectric constant, 2Pr and capacitance were quite dependent on the thermal heat treatment. The measured 2Pr value on the BNdT capacitor annealed at 650C was 56 C/cm² at an applied voltage of 5 V. No fatigue was observed up to 8 × 10¹⁰ read/write switching cycles at a frequency of 1 MHz regardless of annealing temperatures.     

Piezoelectric and ferroelectric properties of textured (Na0.50K0.47Li0.03)(Nb0.8Ta0.2)O3 ceramics by using template grain growth method

(Na_0.50K_0.47Li_0.03)(Nb_0.8Ta_0.2)O₃ ceramics were fabricated by tape casting technique and template grain growth method with sintering additives. The Li and Mn 1 mol% sintering additives are highly efficient for textured grain growth method in (Na_0.50K_0.47Li_0.03)(Nb_0.8Ta_0.2)O₃ ceramics. Grains are well-oriented and piezoelectric coefficient d ₃₃ is 310 pC/N. Piezoelectric coefficients d ₃₃ are proportional to the grain orientations in ceramics prepared by various methods. Ferroelectric phase transition temperature is increased in oriented ceramics. Ferroelectric polarization is decreased but coercive field is increased in the oriented ceramics.     

The Effect of La-Doped Bi4Ti3O12 Buffer Layer on Crystallinity and Ferroelectric Properties of PbZr0.58Ti0.42O3/Bi3.25La0.75Ti3O12 Multilayered Thin Films

PbZr_0.58Ti_0.42O₃ (PZT) ferroelectric thin films with Bi_3.25La_0.75Ti₃O₁₂ (BLT) buffer layer of various thickness were fabricated on Pt/TiO₂/SiO₂/p-Si(100) substrates by rf-magnetron sputtering method. The pure PZT film showed (111) preferential orientation in the XRD patterns, and the PZT/BLT films showed (110) preferential orientation with increasing thickness of the BLT layer. There were no obvious diffraction peaks for the BLT buffer layer, for its thin thickness in PZT/BLT multilayered films. There were the maximum number of largest-size grains in PZT/BLT(30 nm) film among all the samples from the surface images of FESEM. The growth direction and grain size had significant effects on ferroelectric properties of the multilayered films. The fatigue characteristics suggested that 30-nm-thick BLT was just an effective buffer layer enough to alleviate the accumulation of oxygen vacancies near the PZT/BLT interface. The comparison of these results suggests that the buffer layer with an appropriate thickness can improve the ferroelectric properties of multilayered films greatly.     

Electrical properties of Bi4Ti3O12 textured by screen printing

The focus of this work is to explore the electrical properties of bismuth titanate, Bi₄Ti₃O₁₂, textured through the process of screen printing. Textured BTO samples were produced using the templated grain growth technique and the electrical properties were measured both within and normal to the texture plane. The relative permittivity and polarization were determined as a function of electric field, temperature, and frequency. The electrical properties improved dramatically (P_r?=?25 ??C/cm², ??_r(??)?=?1800 at 1 MHz) compared to a randomly oriented sample (P_r?=?10 ??C/cm², ??_r(??)?=?850 at 1 MHz) when measured within the texture plane. A corresponding reduction of electrical properties normal to the texture plane was observed (P_r?=?2 ??C/cm², ??_r(??)?=?300 at 1 MHz). The electrical properties of bismuth titanate textured by screen printing compare favorably to other texture-inducing techniques such as tape casting and hot forging.     

Inverse Capacitance-Voltage Characteristics of Bi3.25La0.75Ti3O12 Thin Film Pulsed Laser Deposited on Thermally Oxidized n-Type Si Substrates

Comparative studies on the electrical properties of a metal-ferroelectric-insulator-semiconductor field effect transistor were conducted using pulsed laser ablated ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films deposited on SiO₂/Si substrates with different SiO₂ thicknesses. The SiO₂ layer was prepared on n-type Si substrates by dry oxidation at a temperature of 800°C. Small angle x-ray reflectivity studies were used to measure the SiO₂ thickness. The capacitance-voltage (C-V) measurements revealed that the films showed good interfacial properties. Shifts in flatband voltages were observable, but were effectively reduced by deposition of the ferroelectric films. Au/BLT/SiO₂/Si diodes with 8 nm SiO₂ layer showed to be stable with relatively large memory window values of about 0.3 V, 2.5 V, 5.0 V, and 7.0 V, at increasing bias voltages of ±5 V, ±7 V, ±10 V, and ±12 V, respectively.     

Oriented growth of Bi3.25La0.75Ti3O12 thin films on RuO2/SiO2/Si substrates by using the polymeric precursor method: Structural, microstructural and electrical properties

c-axis oriented Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were grown on a RuO₂ top electrode deposited on a (100) SiO₂/Si substrate by the polymeric precursor method. X-ray diffraction and atomic force microscope investigations indicate that the films exhibit a dense, well crystallized microstructure having random orientations with a rather smooth surface morphology. The electrical properties of preferred oriented Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films deposited on RuO₂ bottom electrode leaded to a large remnant polarization (P _r ) of 17.2 μC/cm² and (V _c ) of 1.8 V, fatigue free characteristics up to 10¹⁰ switching cycles and a current density of 2.2 μA/cm² at 5 V. We found that the polarization loss is insignificant with nine write/read voltages at a waiting time of 10,000 s. Independently of the applied electric field the retained switchable polarization approached a nearly steady-state value after a retention time of 10 s.     

Textured-Ba(Zr,Ti)O<Subscript>3</Subscript> piezoelectric ceramics fabricated by templated grain growth (TGG)

Ba(Zr_0.085Ti_0.915)O₃ (BZT) ceramics were grain-oriented (textured) in the <001>-orientation using the Templated Grain Growth (TGG) process. The piezoelectric response of the textured samples was enhanced when poled and measured in the <001>-textured direction. The d₃₃-coefficients for samples measured with a low drive field (<5 kV/cm) displayed values as high as ∼975 pC/N. These d₃₃-coefficients were at least three times greater than randomly-oriented BZT ceramics and equally greater than many lead-free piezoelectric ceramics reported in literature. This work successfully demonstrated that grain-oriented BZT ceramics display piezoelectric coefficients (d₃₃-coefficients) that are similar to currently used lead-based materials. This strategy may allow these ceramics to potentially replace some of the lead-based ceramics that are currently being used in various low-temperature and low-drive piezoelectric applications.     

The effect of Bi4Ti3O12 particles addition in lead-free Bi0.5(Na0.75K0.25)0.5TiO3 ceramics

We studied the effect of Bi₄Ti₃O₁₂ (BiT) platelet addition in Bi_0.5(Na_0.75K_0.25)_0.5TiO₃ (BNKT) ceramics by preparing two kinds of BNKT ceramics. One type of BNKT ceramic was fabricated by a conventional solid state reaction method (normal sample), while the other by addition of 15 wt% BiT platelets to BNKT powders (BiT-added sample). In the case of BiT-added BNKT ceramics, plate like grains were formed by the reaction of BiT platelets with Na₂CO₃, K₂CO₃, and TiO₂ during the sintering process. The grain size of BiT-added BNKT ceramics was 10 times larger than that of normal BNKT ceramic. The piezoelectric strain and d₃₃ values of BiT-added BNKT ceramics were 0.135% and 225 pm/V, respectively. These values were 35% higher than those of normal BNKT ceramics. The piezoelectric properties of BiT-added BNKT ceramics were enhanced by the higher domain activity due to a decrease in domain density at larger grain sizes.     

Fabrication and electrical properties of textured Na1/2Bi1/2TiO3-BaTiO3 ceramics by reactive-templated grain growth

The <001> fiber-textured Na_1/2 Bi_1/2TiO₃-BaTiO₃ (6 mol% BaTiO₃) ceramics were fabricated by reactive-templated grain growth (RTGG), using plate-like Bi₄Ti₃O₁₄ (BiT) particles prepared by a molten salt method as templates. The effects of sintering conditions on texture development and microstructure evolvement were both studied, and the mechanisms of grain orientation and densification were discussed. High Lotgering factor (≥96%) and high density (≥96% theoretic density) textured Na_1/2 Bi_1/2TiO₃-6BaTiO₃ ceramics were prepared by using the max templates concentration supplying 100% Bi in the final product, and sintering at 1200 °C for 10 h. The NBT-6BT obtained exhibited good piezoelectric performance with piezoelectric coefficient d ₃₃ ?=?241pC/N, and electromechanical coupling factor k _p ?=?41.2%, k _t ?=?66.5% at room temperature.     

Structure of sol-gel prepared ferroelectric Bi3.4La0.6Ti3O12

The Bi_3.4La_0.6Ti₃O₁₂ (BLT) thin film and powder have been prepared by a sol-gel method with annealing at 700^°C. Randomly oriented BLT thin film exhibits a large remanent polarization, 2P _r = 72 μC/cm², with a dc applied field strength of 320 kV/cm. Structure of sol-gel derived BLT powder has been investigated by neutron scatterings, and refined by a Rietveld method resulting a reasonable goodness of fit (wR _p = 6.7%, and R _p = 5.7%) using an orthorhombic (B2cb, a = 5.4221 Å, b = 5.4032 Å, and c = 32.8361 Å). Two different TiO₆ octahedra exhibit different polarization directions; (100) from Ti(1)O₆, and (011) from Ti(2)O₆, which explains the observed large 2P _r of the randomly oriented BLT thin film.     

Electrical and Ferroelectric Properties of the Bi3.9La0.1Ti2.9V0.1O12 (BLTV) Thin Films

On the SiO₂/Si(100) substrates, Bi_3.9La_0.1Ti_2.9V_0.1O₁₂ (BLTV) ferroelectric thin films were deposited to form a metal-ferroelectric-metal (MFM) structures and improved by the low temperature supercritical carbon dioxide fluid (SCCO₂) post-treatment process. The dielectric and ferroelectric characteristics of the as-deposited BLTV thin films were measured and investigated by the XPS, C-V, and J-E measurement. From the measured results, after the SCCO₂ post-treatment, the capacitance, leakage current density, coercive field, and remnant polarization of the BLTV thin films were all improved obviously. Finally, the mechanism concerning the dependence of electrical properties of the ferroelectric thin films was also investigated.     

Piezoelectric properties of (Na0.465K0.465Bi0.07)(Nb0.93Ti0.07)O3 ceramics with MnO2 addition

In this study, (Na_0.465K_0.465Bi_0.07)(Nb_0.93Ti_0.07)O₃ ceramics with MnO₂ addition were prepared by conventional mixed oxide method. The effects of MnO₂ addition on the structural and electrical properties of the specimens were investigated for the application of piezoelectric devices. As the results of X-ray diffraction analysis, all specimens showed the typical polycrystalline perovskite structure without presence of the second phase. Sintered densities increased with increasing the addition amount of MnO₂ and the specimen added with 0.06 mol% of MnO₂ showed the maximum value of 4.87 g/cm³. Average grain size increased and densification increased with an increasing of MnO₂ contents. The electromechanical coupling factor, dielectric constant, dielectric loss, d₃₃ and Curie temperature of the 0.06 mol% of MnO₂ doped (Na_0.465K_0.465Bi_0.07)(Nb_0.93Ti_0.07)O₃ specimens were 0.32, 1309, 0.016, 122 and 465 °C, respectively.