Fatigue and retention properties of Bi3.25La0.75Ti3O12 films using LaNiO3 bottom electrodes

Fatigue-free Bi_3.25La_0.75Ti₃O₁₂ (BLT) thin films were grown on LaNiO₃ bottom electrodes grown in a microwave furnace at 700 °C for 10 min from the polymeric precursor method. It was found that LaNiO₃ (LNO) bottom electrode with pseudocubic structure strongly promote the formation of (00l) texture of BLT films. The remanent polarization (P_r) and the drive voltage (V_c) were 11 μC/cm² and 1.3 V respectively, and are better than the values found in the literature. The polarization of the Au/BLT/LNO/SiO₂/Si (100) capacitors with a thickness of 280 nm exhibited no degradation after 1 × 10¹⁰ switching cycles at an applied voltage of 5 V with a frequency of 1 MHz. After several tests the capacitors retain 77% of its polarization upon a retention time of 10⁴ s.     

硅衬底Bi4Ti3O12和Bi3.25La0.75Ti3O12铁电薄膜的慢正电子束研究

对硅衬底生长的Bi4Ti3O12和Bi3.25La0.75Ti3O12薄膜样品测量了慢正电子多普勒展宽谱,得到了S参数随正电子注入能量的变化。通过对S参数和W参数的分析,讨论了这类材料中的捕获态特征和结构特点,结果表明,薄膜与硅衬底界面的缺陷为空位-氧复合体,La的掺杂有助于阻止空位-氧复合体向界面的扩散。     

C-axis-oriented Bi3.25La0.75Ti3O12 ferroelectric thin film fabricated by chemical solution deposition

C-axis-oriented Bi_3.25La_0.75Ti₃O₁₂ (BLT) ferroelectric thin films were successfully prepared by chemical solution deposition. According to X-ray diffraction, it is found that the orientation degree increases with the increase of sintering temperature, and at the same time the grain morphology changes from equiaxed to plate-like. Due to the dense morphology and [Bi₂O₂]²⁺ layer of c-preferred orientation of BLT film sintered at 650 °C, it exhibits the lowest leakage current density at room temperature. Additionally, a linear relation between V^0.5 and log(J / T²) is found, suggesting the behavior of leakage current of BLT films obeys the Schottky emission model. P–E loops show that the c-axis-oriented BLT ferroelectric film exhibits low polarization and small coercive field.     

Comparison of Pb(Zr,Ti)O3 capacitors sandwiched with conductive La0.5Sr0.5CoO3 and non-conductive Bi3.25La0.75Ti3O12 layers

Ferroelectric capacitors of Bi_3.25La_0.75Ti₃O₁₂/PbZr_0.4Ti_0.6O₃/Bi_3.25La_0.75Ti₃O₁₂ (BLT/PZT/BLT) and La_0.5Sr_0.5CoO₃/PbZr_0.4Ti_0.6O₃/La_0.5Sr_0.5CoO₃ (LSCO/PZT/LSCO) are fabricated, respectively, on Si substrates in order to study the properties of PZT film sandwiched by conductive oxide and non-conductive oxide layers. It is found that the crystallinity of PZT film grown on LSCO electrode is much better than that on BLT film although the growth temperature of BLT/PZT/BLT is 100 °C higher than that of LSCO/PZT/LSCO. Remanent polarization of LSCO/PZT/LSCO capacitors measured at 10 V is 31.1 μC/cm², which is much higher than the value of 19.8 μC/cm² for BLT/PZT/BLT. Both kinds of the capacitors are fatigue-free up to 10¹⁰ switching cycles. The leakage current density measured at 5 V is about 4.7 × 10^− 6 A/cm² and 1.9 × 10^− 5 A/cm² for BLT/PZT/BLT and LSCO/PZT/LSCO, respectively. The differences for the two kinds of capacitors are discussed in the article.     

Impact of Pt bottom electrode on the properties of ferroelectric Bi3.25La0.75Ti3O12 capacitors

Lanthanum-modified bismuth titanate (Bi_3.25La_0.75Ti₃O₁₂) (BLT) films have been prepared on platinized silicon substrates using sol–gel method. Highly (001) or (111) oriented platinum layers are used as the bottom electrodes of ferroelectric BLT capacitors to study the effects of Pt orientation on the structural and physical properties of BLT films. X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements demonstrate that the microstructure and morphology of BLT films are not strongly affected by the Pt films. BLT film on highly (111) oriented Pt possesses much higher remanent polarization (∼ 8 μC/cm²) than that on highly (001) oriented Pt although the coercive fields of the two kinds of Bi_3.25La_0.75Ti₃O₁₂ films are almost equal.     

Phonon spectra of eulytite crystals Bi4M3O12 (M = Ge,Si): ab initio study

In this paper we present the results of ab initio DFT calculation of phonon spectra for bismuth ortho-germanate Bi₄Ge₃O₁₂ and bismuth ortho-silicate Bi₄Si₃O₁₂ crystals, in the center of the first Brillouin zone. First, the geometry optimization was performed using the analytical energy gradients, with respect to atomic coordinates and unit cell parameters. Vibrational frequencies and normal modes were calculated within the harmonic approximation by diagonalizing the mass-weighted Hessian matrix. The IR and Raman spectra of both crystals were simulated with the periodic ab initio Crystal 09 code and B3LYP hybrid functional and the two sets of Transverse-Optical and Longitudinal-Optical frequencies are generated, together with their intensities. Also, the influence of isotopic substitution for Bi, Ge and O in phonon modes and the picture with values of frequencies shift in each mode by isotopic substitution were calculated. The obtained results are discussed and the comparision between the computed spectra and experimental data is quite satisfactory, which justifies the model and simulation scheme used for the title systems.     

微波诱发溶胶-凝胶自燃烧法一步合成单相Bi3.25La0.75Ti3O12纳米粉体

将溶胶-凝胶法与微波自然烧法相结合,利用微波诱发自燃烧技术一步合成了Bi3.25La0.75Ti3O12(BLT)纳米粉体.根据相关络合反应及其反应平衡常数所进行的理论计算,确定了前驱体溶液的最佳pH值和柠檬酸(CA)/金属离子(M)的物质的量比.分别利用红外光谱(FTIR)、X射线衍射(XRD)和扫描电镜(SEM)对前驱体及合成的纳米粉体进行了表征,结果表明,微波诱发溶胶-凝胶自燃烧法能一步合成具有层状钙铁矿结构的单相BLT纳米粉体.当pH=6、n(CA)/n(M)=2.5以及氧化度Q=80 %时,合成的单相BLT纳米粉体的平均晶粒尺寸约为30nm.     

Annealing temperature and ultraviolet irradiation effect on the ferroelectric properties of Bi(3.25)La(0.75)Ti3O12 thin films

Bi(3.25)La(0.75)Ti3O12 thin films were prepared on Pt/Ti/SiO2/Si substrates by the metal organic decomposition method. The structural characterizations and the surface morphology observations were carried out applying X-ray diffraction and atomic force microscope, respectively. The annealing temperature and the ultraviolet irradiation effect on the ferroelectric properties were studied. It was found that the remnant polarization (Pr) and the coercive field (Ec) increased with the increase of the applied electric field (E) for all films. With the annealing temperature increasing from 670 degrees C to 750 degrees C, the increase tendency of Pr(E) and Ec (E) got enhanced from 670 degrees C to 720 degrees C, followed by weakened from 720 degrees C at 750 degrees C. These phenomena could be well explained by the different internal strain in films. The remnant polarization and the coercive field showed an obvious decrease when the top electrodes of the thin films were illuminated with UV light due to the screening effect of trapped charge carries.     

Leakage mechanisms in rare-earth (La,Nd) doped Bi4Ti3O12 ferroelectric ceramics

Dense Bi₄Ti₃O₁₂ (BTO), Bi_3.15La_0.85Ti₃O₁₂ (BLaT) and Bi_3.15Nd_0.85Ti₃O₁₂ (BNdT) ferroelectric ceramics were synthesized by solid–state reaction method. All ceramics are orthorhombic bismuth-layered perovskite structure with plate-like grains of random orientation. The influences of La and Nd doping on the ferroelectric properties and leakage mechanism were investigated. The remanent polarizations (2P _r) were determined to be 13.4, 23.9 and 32.6 μC/cm² for BTO, BLaT, and BNdT, respectively. The leakage current density decreased markedly with La and Nd doping. The dominant leakage mechanism in both BTO and BLaT ceramics has been found to be the ohmic mechanism and the space-charge-limited current mechanism in the low and high electric field region, respectively. While in BNdT ceramics a quasi-ohmic behavior was found in the high electric field region, following the ohmic behavior in the low electric field region and trapped filled limited behavior in the intermediate electric field region.     

Effects of oxygen partial pressure and ion doping on the ferroelectricity and microstructures of sputter-deposited Bi3.25La0.75Ti3O12 films

The effects of oxygen partial pressure during deposition and V and P doping on the microstructures and ferroelectricity of sputter-deposited Bi_3.25La_0.75Ti₃O₁₂ (BLT) films on Pt/SiO₂/Si(100) were studied. At the deposition pressure of 4 mTorr the O₂/(Ar+O₂) ratio in the range of 0.4–0.5 allowed the films to achieve a larger remnant polarization (2P_r). For the (Bi_3.25La_0.75)(Ti_3−xV_x)O₁₂ films, the 2P_r first increases with increasing the V concentration (x) up to 0.03, then gradually decreases in the range of x=0.05–0.1 and drastically decreases at x=0.15. The doping of V into the BLT films can simultaneously induce two contrary effects on the 2P_r, i.e., reducing the amount of oxygen vacancies and decreasing the grain size, which result in the improvement and degradation of 2P_r, respectively. The two effects are similar to those induced by the factor of oxygen partial pressure during deposition. The degradation of 2P_r for the P-doped BLT films can be ascribed to the dissociation of BiO bonds and reduction of grain size due to P doping.     

Dielectric enhancement of the trilayered Bi3.15Eu0.85Ti3O12/Bi3.15Nd0.85Ti3O12/Bi3.15Eu0.85Ti3O12 thin film deposited on Pt/Ti/SiO2/Si substrate

The trilayered Bi_3.15Eu_0.85Ti₃O₁₂/Bi_3.15Nd_0.85Ti₃O₁₂/Bi_3.15Eu_0.85Ti₃O₁₂ (BET/BNT/BET) thin film was deposited on Pt/Ti/SiO₂/Si(100) substrates by metal organic decomposition at annealing temperature of 650 °C, and the microstructure, chemical composition, leakage current, dielectric and ferroelectric properties were investigated by field emission scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, semiconductor characterization system, impedance analyzer and ferroelectric tester. The trilayered thin film is of crack-free and dense surface with some discrete cluster distribution, and typical Bi-layered perovskite polycrystalline phase. The dielectric constant ε _r and dissipation factor tanδ are 1,233 and 0.0215 at 100 kHz for the trilayered thin film. Comparing with the pure BET and BNT thin films, the dielectric constant of trilayered thin film is enhanced, which is due to the space charge and the intermediate superlattice. The trilayered thin film shows excellent dielectric properties and can be promisingly used for the high dielectric layer of silicon-based embedded capacitors in package substrate.     

Luminescent characteristics of LiSrBO3:M (M = Eu, Sm, Tb, Ce, Dy) phosphor for white light-emitting diode

LiSrBO₃:M (M = Eu³⁺, Sm³⁺, Tb³⁺, Ce³⁺, Dy³⁺) phosphors which have been developed for white light-emitting diodes (LEDs) were synthesized by a normal solid-state reaction. The emission and excitation spectra indicate that these phosphors can be effectively excited by near-ultraviolet light-emitting diodes (UVLED), and exhibit satisfactory red, green and blue performances, respectively, nicely fitting in with the widely applied UV chip. Under the condition of doping charge compensation Li⁺, Na⁺ and K⁺, the luminescence intensities of these phosphors were increased.     

Photoluminescence properties of novel KBaBP2O8:M (M = Pb2+ and Bi3+) phosphors

A series of novel inorganic phosphors KBa_1−xPb_xBP₂O₈ and K_1+xBa_1−2xBi_xBP₂O₈ (0.01 ⩽ x ⩽ 0.08) were synthesized by using a solid-state reaction technique at high-temperature and their photoluminescence properties were investigated. The dependence of the emission intensity on the Pb²⁺ and Bi³⁺ concentration for the KBa_1−xPb_xBP₂O₈ and K_1+xBa_1−2xBi_xBP₂O₈ was studied, in which the optimal concentration as well as the critical transfer distance R_c for Pb²⁺ and Bi³⁺ was obtained and determined. The as-prepared phosphors can be effectively excited with ultraviolet (UV), and exhibit UV − blue emission with large Stokes shift. The above work indicates these phosphors could be potential candidates for application in UV lamps industry.     

Synthesis and luminescent properties of SrZnO2:Eu3+,M+ (M = Li,Na, K) phosphor

In this paper, a series of novel luminescent materials, SrZnO₂:Eu³⁺,M⁺ (M = Li, Na, K) have been synthesized by conventional solid-state reaction. X-ray diffraction (XRD) patterns and photoluminescence (PL) spectra were carried out to characterize their structural and luminescent properties. It was found that under ultraviolet excitation with a wavelength of 301 nm, SrZnO₂:Eu³⁺ gives a red luminescence that was attributed to the transitions from ⁵D₀ excited states to ⁷F_J (J = 0–4) ground states of Eu³⁺ ions. The feature and the high intensity of hypersensitive transition ⁵D₀ → ⁷F₂ indicate that Eu³⁺ prefers to occupy a low symmetry site. The incorporation of alkali metal ions greatly enhanced the luminescence intensity and slightly changed the excitation and emission peak position, probably due to the influence of the coordination conditions for Eu³⁺ ions.     

High dielectric constant and low-loss dielectric ceramics of Ba5LnZnNb9O30 (Ln = La,Nd and Sm)

Polycrystalline Ba₅LnZnNb₉O₃₀ (Ln = La, Nd and Sm) ceramics were prepared as single-phase materials through conventional solid-state ceramics route. The structure was characterized by X-ray diffraction methods and scanning electron microscopy (SEM) and the dielectric properties were measured from − 120 °C to 150 °C. All three compounds are paraelectric phases adopting the filled tetragonal tungsten–bronze (TB) structure at room temperature, and the Curie temperature (at 1 MHz) were − 60, − 25 and − 5 °C for Ba₅LaZnNb₉O₃₀, Ba₅NdZnNb₉O₃₀, and Ba₅SmZnNb₉O₃₀ respectively. At 1 MHz their dielectric constant (ε_r) varies from 258 to 310, dielectric loss (tanδ) from 0.0033 to 0.0068, and the temperature coefficients of the dielectric constant (τ_ε) from − 1220 to − 1390 ppm °C^− 1.     

Ab initio study of AlCu2M (M = Sc,Ti and Cr) ternary compounds under pressures

The structural, electronic and elastic properties of the AlCu₂M (M = Sc, Ti and Cr) compounds in the pressure range of 0–100 GPa was investigated based on density functional theory. The calculated lattice parameters of the AlCu₂M compounds at zero pressure and zero temperature are in very good agreement with the existing experimental data. The bulk modulus, shear modulus and Young’s modulus increases with the increase of pressure, which indicates that higher materials hardness may be obtained when increasing pressures. The bulk modulus and Young’s modulus of AlCu₂Cr is the greatest under pressure. The shear modulus of AlCu₂Ti is the highest above 30 GPa, while that of the AlCu₂Sc is the strongest below 30 GPa. The calculated B/G values at zero and higher pressure indicated that they are ductile materials. The electronic densities of states and bonding charge densities have been discussed in details, revealing these compounds exhibit half-metallic behavior. In addition, the pressure dependences of Debye temperatures of AlCu₂M compounds have also been calculated. The results indicate that Debye temperatures increase with increasing pressure.     

Structure and magnetic properties of sputtered FePtM (M = Ti,Nb) thin films

FePt thin films doped with various Ti and Nb concentrations ranging from 2.9 to 9.1 at.% were prepared by r.f. magnetron sputtering. The structural and magnetic properties of Ti- and Nb-doped FePt thin films were investigated. Structural studies revealed that the long range ordering in FePt thin films depends on the doping concentration and annealing temperature of FePt thin films. The addition of Ti and Nb is found to enhance the grain refining in FePt thin films. The effects of doping concentration on the magnetic properties of FePt thin films were studied and discussed.     

VUV–UV spectroscopic properties of RE (RE = Ce, Eu and Tb)-doped KMLn(PO4)2 (M = Ca, Sr; Ln = Y, La, Lu)

The VUV excited luminescent properties of Ce³⁺, Eu³⁺ and Tb³⁺ in the matrices of KMLn(PO₄)₂ (M²⁺ = Ca, Sr; Ln³⁺ = Y, La, Lu) were investigated. The bands at about 155 nm in the VUV–UV excitation spectra are attributed to the host lattice absorption, which indicates that the optical band gap of KMLn(PO₄)₂ is about 8.0 eV. Ce³⁺-doped samples show typical Ce³⁺ emission in the range of 300–450 nm, and the energy transfer from host lattice to Ce³⁺ is efficient. For Eu³⁺-doped samples, the O²⁻–Eu³⁺ CTBs are observed to be at about 228 nm except KSrLu(PO₄)₂:Eu³⁺ (247 nm). As for Tb³⁺-doped samples, typical 4f → 5d absorption bands in the region of 175–250 nm were observed.     

The synthesis and selected properties of new double vanadates M2InV3O11, where M = Zn,Mg

New compounds Zn₂InV₃O₁₁ and Mg₂InV₃O₁₁ were first obtained as a result of solid-state reactions. The crystallographic system and the unit cell parameters of these compounds were determined, their melting temperatures and the way of melting were established, also IR investigations were conducted.