Bi3.25La0.75Ti3O12 Research Articles

Synthesis, consolidation and dielectric properties of BLT ceramics processed by M-PVA gel ignition technique

Polycrystalline samples of lanthanum modified bismuth titanate ceramics with composition Bi3·25La0·75Ti3O12 (BLT) were prepared at three different sintering temperatures (1050, 1100 and 1150°C) using M-PVA gel ignition technique. The samples were characterised for structural and electrical properties. A significant amount of as burnt BLT powder was found to be crystalline in nature having a yellowish colour. Very fine BLT nanoparticles were characterised by TEM analysis. Single phase with orthorhombic crystal structure was observed for all the samples, confirmed by X-ray analysis. Dielectric properties were studied as a function of frequency and temperature. More than 95% relative density was observed for all the three sintered samples. The sample sintered at 1100°C showed highest dielectric constant and relative density and lowest loss.

Mechanical stress modified ferroelectric aging behavior

Mechanical stress effect on aging behavior of Bi3.25La0.75Ti3O12 (BLT) and PbZr0.53Ti0.47O3 (PZT) films was investigated. It is found that the remnant polarization decreases with time while the coercive field increases in stress-free BLT films. For unconfined PZT films, both the remnant polarization and the coercive field decrease as time elapses. The applied tensile stress weakens the aging of remnant polarization of BLT films but strengthens the aging of coercive field, while the applied tensile stress possesses opposite effect. In contrary, the applied compressive stress simultaneously improves the aging behavior of both remnant polarization and coercive field of PZT films. Mechanical-stress-induced variation of domain wall mobility in different materials was suggested as the possible origin of these observations. This work indicates that the aging behavior modification using stress could be realized, and it is helpful for promoting the reliability of ferroelectric films for industrial applications.

Photocatalytic degradation of an azo dye using Bi3.25M0.75Ti3O12 nanowires (M= La, Sm, Nd, and Eu)

Abstract Bi3.25M0.75Ti3O12 (BMT, M = La, Sm, Nd, and Eu) nanowires were synthesized through simple hydrothermal route and their structural and photocatalytic properties were investigated. XRD results indicated that these compounds are of layered perovskites structure. In addition, the band gaps of Bi3.25La0.75Ti3O12 (BLT), Bi3.25Sm0.75Ti3O12 (BST), Bi3.25Nd0.75Ti3O12 (BNT), and Bi3.25Eu0.75Ti3O12 (BET) were estimated to be about 2.403, 2.594, 2.525, and 2.335 eV, respectively. Their photocatalytic activities were evaluated by photocatalytic degradation of methyl orange (MO) under visible light irradiation (λ > 420 nm). Bi3.25M0.75Ti3O12 (M = La, Sm, Nd, and Eu) showed markedly higher catalytic activity compared to traditional N doped TiO2 (N-TiO2) and pure bismuth titanate (Bi4Ti3O12, BIT) for MO photocatalytic degradation under visible light irradiation. The high photocatalytic performance of Bi3.25M0.75Ti3O12 photocatalysts could be attributed to the strong visible light absorption and the recombination restraint of the e−/h+ pairs resulting from doping of rare earth metal ions. Furthermore, BET nanowires exhibited the highest photocatalytic activity.

X-ray Absorption Spectroscopy Identification of Mn-doped Bi3.25La0.75Ti3O12 Ceramics

In this work, x-ray absorption spectroscopy was performed to characterize Mn-doped Bi3.25La0.75Ti3O12 (BLT) ceramics with various MnO2 dopants. The x-ray absorption near-edge structure (XANES) was analyzed in combination with first principle calculation of Mn K-edge to identify atomic position of Mn in BLT. The result confirms Mn4+ substituting on Ti4+-site in BLT. Further, the extended x-ray absorption fine structure (EXAFS) was examined where Mn K-edge of Mn-doped BLT was compared to that of Ti K-edge of BLT in R-space. The result shows radial distances between Mn4+ and O2− ions in ab-axis are almost equal and decrease with increasing Mn-doping contents. This is strong evidence that Mn4+ substituting on Ti4+ site can be reduced the orthorhombicity, which increase the polarization domains size and enhance remnant polarization, speed up the polarization domains movement and lessen coercive field.

Electric Properties and Interface Charge Trap Density of Ferroelectric Gate Thin Film Transistor Using (Bi,La)4Ti3O12/Pb(Zr,Ti)O3 Stacked Gate Insulator

We successfully fabricated ferroelectric gate thin film transistors (FGTs) using solution-processed (Bi,La)4Ti3O12 (BLT)/Pb(Zr,Ti)O3 (PZT) stacked films and an indium–tin oxide (ITO) film as ferroelectric gate insulators and an oxide channel, respectively. The typical n-type channel transistors were obtained with the counterclockwise hysteresis loop due to the ferroelectric property of the BLT/PZT stacked gate insulators. These FGTs exhibited good device performance characteristics, such as a high ON/OFF ratio of 106, a large memory window of 1.7–3.1 V, and a large ON current of 0.5–2.5 mA. In order to investigate interface charge trapping for these devices, we applied the conductance method to MFS capacitors, i.e., Pt/ITO/BLT/PZT/Pt capacitors. As a result, the interface charge trap density (Dit) between the ITO and BLT/PZT stacked films was estimated to be in the range of 10-11–10-12 eV-1 cm-2. The small Dit value suggested that good interfaces were achieved.

Electrical and Physical Properties of the Bi3.25La0.75Ti3O12 Ferroelectric Thin Films Prepared by Conventional Temperature Annealing Process

We have investigated the structure and ferroelectric properties of the Bi3.25La0.75Ti3O12 (BLT) thin films on SiO2/Si substrate fabricated by sol-gel method. We used the BLT films were annealed at various temperatures of 600, 650, and 700°C for one hour by conventional furnace annealing (CTA). The temperature dependence of leakage currents densities of ferroelectric BLT thin films. The crystalline structure of the prepared BLT thin films was analyzed by X-ray diffraction (XRD). Field emission scanning electron microscopy (FESEM) was used to observe the film thickness and the surface morphology including grain size and porosity. The leakage current density and capacitance of thin film were measured by HP4156C.

Study on Dielectric Relaxation in BiFeO<sub>3</sub>/Bi<sub>3.25</sub>La<sub>0.75</sub>Ti<sub>3</sub>O<sub>12</sub> Film

BiFeO3 (BFO) film is considered as relaxor ferroelectric film with a leakage current, and Bi3.25La0.75Ti3O12 (BLT) film is regarded as ferroelectric film with a leakage current. Maxwell- Wagner (M-W) theory has been used to study the dielectric relaxation behavior of BiFeO3 (BFO)/Bi3.25La0.75Ti3O12 (BLT) films grown on Pt/Ti/SiO2/Si substrate. Results show that the characteristics of BFO film significantly affect the dielectric relaxation behavior of the BFO/BLT film. The theoretical results agree well with the experimental data when the temperature is above 400K. It is inferred that the polycrystalline orientation of BFO film leads to the presence of disorganized polar nanoregions (PNRs) in BFO film. And BFO film exhibits relaxation characteristics at high temperatures.

Effects of Ion Doping at Different Sites on Electrical Properties of Ferroelectric Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> Ceramics

Pure, La3+doped at A site, V5+doped at B site, and La3+and V5+co-doped ferroelectric Bi4Ti3O12(BTO), Bi3.25La0.75Ti3O12(BLT), Bi4Ti2.98V0.02O3(BTV) and Bi3.25La0.75Ti2.98V0.02O12(BLTV) were successfully prepared by conventional sintering technique. The structures of the ceramics were investigated by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. X-ray diffraction indicated that assemblages of all sintered ceramics consist of a single phase of Bi4Ti3O12, implying that the A-site La3+and B-site V5+substitutions in this case do not affect the layered structure. Among these ceramics, BLTV ceramic exhibited the best electrical properties. The leakage current density of BLTV ceramic was only 1.3×10-4Acm-2at 40 KVcm-1, two orders of magnitude lower than BTO ceramic. Besides, a saturated ferroelectric hysteresis loops with largest remnant polarization 2Pr of 30.6μC/cm2was observed for this sample. These suggested that the co-doped Bi4Ti3O12ceramic by La3+and V5+at A and B sites showed advantages in application over the pure BTO, doped BLT and BTV ceramic, respectively.

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

PbZr0.58Ti0.42O3 (PZT) ferroelectric thin films with Bi3.25La0.75Ti3O12 (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.

The crystalline orientation and ferroelectric properties of Bi3.25La0.75Ti3O12 thin films mediated by the intermediate layer of LaNiO3

c-Axis-oriented and (117)-oriented Bi3.25La0.75Ti3O12 (BLT) thin films are successfully controlled by the intermediate layer of LaNiO3 (LNO) with chemical solution deposition (CSD), respectively. X-ray diffraction (XRD) demonstrates that the structure and orientation of LNO thin films have a strong effect on the orientation of BLT thin films. Scanning electron microscopy suggests that BLT thin films on LNO electrode exhibit crack-free, uniform size grains and dense microstructure. A crystalline orientation dependent remanent polarization is observed in BLT thin films, and it is found that the remanent polarization (2Pr) of (117)-oriented films is larger than that of c-axis-oriented films. Our research directly demonstrates that the vector of the main spontaneous polarization in these layered perovskite materials (BLT) is along a-axis.

Dielectric Functions of Niobium Doped Bi3.25La0.75Ti3O12 Thin Films Using Spectroscopic Ellipsometry

Ferroelectric thin films of Nb doped Bi3.25La0.75Ti3O12 (BLT) were prepared by chemical solution deposition method onto Pt/Ti/SiO2/Si(100) substrates using spin coating technique. From the X-ray diffraction analysis it was found that films were polycrystalline with single phase. The optical properties of the Nb doped BLT thin films were investigated at room temperature in the 0.72–6.2 eV energy range using spectroscopic ellipsometry (SE). Double Tauc–Lorentz (DTL) dispersion relation was successfully fitted in the uv/visible region. Value of the full width at half maxima (Г) in dielectric function plots increased with Nb doping. This increase in FWHM may be attributed to the increase in the trap density in forbidden band which consequently decreases the value of Eg. The optical band gap energy (E g d) was found to decrease with increase in Nb doping concentration. This decrease in E g d with doping may be due to the changes in the defect concentration present in the structure.

Study of Ferroelectric Bi3.25La0.75Ti3O12 Thin Films Deposited by Sol-Gel Method

Powders and thin films of ferroelectric Bi3.25La0.75Ti3O12 (BLT) have been prepared from a sol-gel precursor heated at various temperatures, up to 600°C. The BLT precursor and the BLT powders have been characterized by thermal analyses, X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM). Then, the precursor has been used to deposit thin films of ferroelectric BLT on specific silicon substrates, using a specific spin coating process. The thin films have been characterized by XRD, SEM and ellipsometry. Electrical polarization analyses have been finally performed on these films, and performing remnant polarization has been obtained.

Effect of annealing pressure on structure and properties of ferroelectric Bi3.25La0.75Ti3O12 thin films prepared by sol–gel method

The effect of annealing pressure was investigated for Bi3.25La0.75Ti3O12 (BLT) thin films prepared on Pt/TiO2/SiO2/p-Si(100) substrates by sol–gel method. The amorphous films were annealed at 750 °C for 30 min under different oxygen pressures varying from 10−4 to 3 atm. The largest Pr of 17.8 μC/cm2 with the Ec of 73.6 kV/cm was obtained for the film annealed under 0.1 atm PO2. Then the structure, crystallization degree, and morphology were characterized by X-ray diffraction (XRD), Raman spectroscopy, and field-emission scanning electron microscope (FSEM) to clarify the effect of annealing pressure on the ferroelectric properties. The XRD and Raman spectroscopy results indicated a clear decreasing of the crystallization degree of the films annealed under 10−4 and 3 atm PO2. FSEM results showed the different growth orientation of grains under different oxygen pressures. This study indicated some important effects of annealing pressure on the physical properties of BLT thin films.

A comparative study on Bi4Ti3O12 and Bi3.25La0.75Ti3O12 ferroelectric thin films derived by metal organic decomposition

The crystal orientations and electrical properties of Bi4Ti3O12 (BIT) and Bi3.25La0.75Ti3O12 (BLT) ferroelectric thin films were studied and compared. Stoichiometric BIT and BLT samples were deposited on Pt(111) substrates and crystallized at 750 °C to get mixed orientations. The BIT sample exhibited a/b axes orientation with (117) component, while the BLT sample was more c-axis oriented. The 2Pr values of such BIT and BLT were 34.3 μC/cm2 and 25.7 μC/cm2, respectively. Nevertheless, BLT has much better leakage current and polarization saturation properties. In order to obtain c-axis oriented BIT thin films, excess bismuth was used. BIT with 15% excess bismuth processed at 750 °C was purely c-axis oriented and only possessed a 2Pr value of 4.9 μC/cm2, while that of 15% excess bismuth BLT sample was 18.3 μC/cm2. This can be attributed to the large polarization anisotropy in BIT, and this anisotropy is reduced by lanthanum doping.

Bi<sub>4</sub>Ti<sub>3</sub>O<sub>12</sub> and Bi<sub>3.25</sub>La<sub>0.75</sub>Ti<sub>3</sub>O<sub>12</sub> Thin Films Prepared by RF Magnetron Sputtering

Bi4Ti3O12 (BTO) and Bi3.25La0.75Ti3O12 (BLT) ferroelectric thin films were deposited on Pt/Si substrates by RF magnetron sputtering with Bi4Ti3O12 (BTO) and Bi3.25La0.75Ti3O12 (BLT) targets with 50-mm diameter and 5-mm thickness. The microstructure and ferroelectric properties of thin films were investigated. The grain growth behavior and ferroelectric properties such as remanent polarization were different in these two kinds of film, the effects of La doping in the BLT thin film were very obvious.

Fabrication of IGZO and In2O3-channel Ferroelectric-gate Thin Film Transistors

AbstractWe have fabricated and characterized ferroelectric-gate TFTs using In-Ga-Zn-O (IGZO) or In2O3 as a channel material. The ferroelectric gate insulator used in this work is (Bi,La)4Ti3O12 (BLT). We observed normal n-channel transistor operation for both IGZO and In2O3-channel TFTs. However, a charge injection type hysteresis was observed for IGZO channel TFTs in drain current – gate voltage (ID-VG) characteristics. Post fabrication anneal at 300oC reduced the charge-injection-tyoe hystereesis and the subthreshold swing was also improved from 0.27 to 0.19 V/decade. On the other hand, when the In2O3 was used as a channel, hysteresis due to the ferroelectric gate insulator was clearly observed in ID-VG characteristics. A memory window of 2V, a subthreshold voltage swing of 0.35V/decade, a field-effect mobility of 1.6 cm2/Vs, and a on/off drain current ratio of more than 10^6 were obtained.

THE EFFECT OF A-SITE La AND Nd SUBSTITUTION ON THE RESIDUAL STRESS OF Bi4Ti3O12 THIN FILMS FABRICATED BY SOL-GEL METHOD

ABSTRACT In this paper, thin films of Bi4Ti3O12 (BTO), Bi3.25La0.75Ti3O12 (BLT) and Bi3.15Nd0.85Ti3O12 (BNT) were fabricated on Pt/Ti/SiO2/Si substrates by sol-gel method. The structures and ferroelectric properties of the polycrystalline films are studied and the correlation between substitution and residual stress are discussed in detail. The results show that, the ferroelectric and fatigue properties of the BLT and BNT films are improved greatly, compared with those of the BTO thin film. The Pr values of BLT and BNT are 13.14 and 21.23 μC/cm2, respectively. X-ray diffraction result shows that the measured residual stress is tensile stress for all films. After A-site substitution, the value of tensile stress for the BTO films has increased and the stress value is maximal for the BNT film. The calculated intrinsic residual stress values are 288.4, 418.4 and 608.2 MPa for BTO, BLT and BNT, respectively.

MAXWELL—WAGNER MECHANISM INDUCED DIELECTRIC RELAXOR IN BiFeO3/Bi3.25La0.75Ti3O12 FILM

Maxwell—Wagner (M-W) theory was used to explain the dielectric relaxor behavior of BiFeO3(BFO)/Bi3.25La0.75Ti3O12(BLT) film grown on Pt/Ti/SiO2/Si substrate. The BFO film was considered to be ferroelectric film, and its temperature dependence of dielectric constant was calculated by Landau theory. BLT film was of dielectric-relaxor behavior and its temperature dependence of dielectric constant was given by Smolenski theory. The leakage currents for the BFO and BLT films were assumed to obey Poole–Frenkel emission and Schottky emission, respectively. The temperature dependent dielectric constant and loss of the BFO/BLT film were characterized, which agrees with the experiment. The enhancement of the polarization in BFO/BLT film may induced by the current leakage restraining in BFO film.

CO-EFFECT OF ANNEALING TEMPERATURE AND AMBIENT ON FERROELECTRIC PROPERTIES OF Bi3.25La0.75Ti3O12 FILMS

ABSTRACT Co-effect of crystallization ambients (O2 and N2 mixed gas) and temperatures (600–800°C) on crystal structures and ferroelectric properties of the sol-gel deposited Bi3.25La0.75Ti3O12 (BLT) films is studied in this work. As the annealing temperature increases, the films get full crystallization and show different orientation. The film annealed in N2 at 650°C is a-axis oriented, and get large Pr but bad fatigue property, which is caused by the charged oxygen vacancies in the films annealed in the oxygen-deficient ambients. The film annealed in 20% O2 at 750°C is random oriented and exhibits excellent ferroelectric properties in terms of the largest Pr value of 11.5 μC/cm2 and the lowest Ec value of 83.3 kV/cm under a voltage of 12 V. Moreover, the film shows good fatigue endurance after 109 switching cycles. The crystllization and growth of the BLT films are sensitive to annealing ambients and temperatures. Therefore, the appropriate annealing ambient and temperature can improve the properties of the ferroelectric films greatly.

Electrical Properties of Au/(Bi,La)4Ti3O12/Pt/SrTa2O6/Si Field-Effect Transistor

The metal-ferroelectric-metal-insulator-semiconductor field-effect transistor using the Au/(Bi,La)4Ti3O12(BLT)/Pt/SrTa2O6(STA)/Si structure is prepared. The STA and BLT films are spun-casted by the sol-gel method. The equivalent oxide thickness value of the STA thin film is 5.2 nm and negligibly small hysteresis loops have been observed for the Au/STA/Si structure. The leakage current density is lower than 10− 7 A/cm2 under 6 V. The remanent polarization of the 420 nm-thick BLT film was 35.2 μ C/cm2 at 450 kV/cm. The Au/BLT/Pt/STA/Si MFMIS-FET was fabricated with different area ratio (AI/AF) from 1 to 8. From the drain current–gate voltage characteristics at the drain voltage of 0.2 V, the memory window is only 0.5 V for the device with AI/AF = 1 but it is increased to 1.8 V as the AI/AF is increased to 8. For the AI/AF ratio of 4, the drain current of 1.2× 10− 5 A rapidly drops after 1.4× 104 s to 4× 10− 6 A. The retention time improves as the AI/AF ratio is increased to 8 and it has been found to drop after 8.5× 104 seconds.