Effect of BiFeO3 doping on ferroelectric properties of Na0.5Bi0.5TiO3–BaTiO3 based thin film derived by sol–gel method

0.94Na_0.5Bi_0.5TiO₃–0.06BaTiO₃ (NBT–6BT) and (0.94 ? x)Na_0.5Bi_0.5TiO₃–0.06BaTiO₃–xBiFeO₃ (NBT–6BT–xBFO, x = 0.03, 0.05 and 0.08) thin films were deposited on Pt/Ti/SiO₂/Si substrates by a sol–gel process. Relative permittivity and remnant polarization were maximized at 5 % BFO substitution. Compared with 0.94NBT–0.06BT, the leakage current density of 0.89NBT–0.06BT–0.05BFO at 600 kV/cm is reduced by one order of magnitude. Enhanced ferroelectricity was also achieved in 0.89NBT–0.06BT–0.05BFO, the remnant polarization (2P _r) values of 0.89NBT–0.06BT–0.05BFO and 0.94NBT–0.06BT are 46 and 24 µC/cm².     

Thermoanalytical study of the synthesis of Na<Subscript>0.5</Subscript>Bi<Subscript>0.5</Subscript>TiO<Subscript>3</Subscript> ferroelectric

The study presents results of examination on Na_0.5Bi_0.5TiO₃ (NBT) ferroelectric synthesis through intermediate binary compound Bi₄Ti₃O₁₂ (BIT). The first stage of the study related to obtaining BIT from oxide precursors, i.e. Bi₂O₃ and TiO₂. The second stage included obtaining NBT from Bi₄Ti₃O₁₂, Na₂CO₃ and TiO₂. Two polymorphic modifications of TiO₂ (anatase, rutile) and diversified initial homogenization of raw material batches were applied during examination.     

Diffuse X-ray scattering in the lead-free piezoelectric crystals Na1/2Bi1/2TiO3 and Ba-doped Na1/2Bi1/2TiO3

X-ray diffuse scattering has been measured by single-crystal X-ray diffraction on the lead-free piezoelectric perovskites Na_0.5Bi_0.5TiO₃ (NBT) and (Na_0.5Bi_0.5)_0.89Ba_0.11TiO₃ (NBT–Ba_0.11). Evidence of a pronounced local structure or included phase different from the rhombohedral average symmetry (space group R3c), or of a modulated structure with a characteristic period of 40 Å, is presented for NBT from high-resolution synchrotron X-ray mapping and CCD diffractometer investigations. The additional scattering shows pronounced anisotropy and produces satellite peaks displaced by 0.2 in the h and k indices for reflections such as {640} indexed on the pseudo-cubic unit cell with a = 7.761(2) Å. By contrast, weaker, less anisotropic diffuse scattering is observed for tetragonal NBT–Ba_0.11 (space group P4mm), which is directed along the pseudo-cubic 〈110〉. The lack of satellite peaks and pronounced anisotropic diffuse scattering in the tetragonal phase of phase NBT–Ba₀.₁₁ lends support to the idea that the massive tetragonal to rhombohedral phase transition in NBT at around 503–573 K, which is absent in NBT–Ba₀.₁₁, may be the key to understanding the local structure found repeatedly at room temperature in this complex material.     

Synthesis and magnetoelectric studies on Na0.5Bi0.5TiO3–BiFeO3 solid solution ceramics

Polycrystalline ceramics of 1 ? x[Na_0.5Bi_0.5TiO₃] ? x[BiFeO₃] (NBT–BFO) were synthesized by the modified Pechini's method to study their magnetic and magnetoelectric properties. A series of solid solutions exhibiting magnetoelectric output were formed when two iso-structural compounds Na_0.5Bi_0.5TiO₃ (NBT) and BiFeO₃ (BFO) were combined. Polarization-electric field hysteresis loops revealed that the maximum polarization (～23 μC/cm² for x = 0.1) decreased continuously with the increase of BFO content, following a hard doped effect. Piezoelectric charge coefficient (d₃₃) = 41 pC/N was obtained for the ceramics with x = 0.1 and the value continues to decrease with the composition. Magnetic hysteresis loops represent the canted antiferromagnetic nature for x ≤ 0.6 and ferromagnetic-like behavior for the BFO-rich compositions. Magnetoelectric coupling was determined by measuring the magnetoelectric voltage coefficient which is ～12.4 mV/cm-Oe at an ac magnetic field of 10 Oe (1 kHz), for x = 0.1 sample.     

Enhancement of Photocatalytic Activity of Sodium Bismuth Titanate by Doping with Copper,Silver, and Tin Ions

Perovskite type oxides, sodium bismuth titanate (Na_0.5Bi_0.5TiO₃), and Ag⁺, Cu²⁺, and Sn²⁺ doped Na_0.5Bi_0.5TiO₃ were prepared by pechini and ion exchange methods, respectively. Photocatalytic activities of these catalysts were tested by decomposition of methylene blue (MB) under visible light irradiation. Results showed that the photocatalytic activity of metal ion doped Na_0.5Bi_0.5TiO₃ was higher than undoped Na_0.5Bi_0.5TiO₃. Relatively high photocatalytic performance of Ag⁺‐doped Na_0.5Bi_0.5TiO₃ is mainly ascribed to the efficient separation of electron‐hole (e^–, h⁺) pairs, lower bandgap energy and the creation of active hydroxyl radicals ( ^? OH). Further, the Ag⁺‐doped Na_0.5Bi_0.5TiO₃ catalyst showed good reusability up to four cycles. A possible mechanism for the enhanced photocatalytic performance was proposed. The synthesized photocatalysts were characterized by XRD, SEM, EDS, XPS, FT‐IR, and UV/Vis DRS techniques.     

Tunable luminescence and energy transfer process between Tb3+ and Eu3+ in GYAG:Bi3+, Tb3+, Eu3+ phosphors

A series of Eu³⁺ ions co-doped (Gd_0.9Y_0.1)₃Al₅O₁₂:Bi³⁺, Tb³⁺ (GYAG) phosphors have been synthesized by means of solvothermal reaction method. The XRD pattern of GYAG phosphor sintered at 1500 °C confirms their garnet phase. The luminescence properties of these phosphors have been explored by analyzing their excitation and emission spectra along with their decay curves. The excitation spectra of the GYAG:Bi³⁺, Tb³⁺, Eu³⁺ phosphors consists of broad bands in the shorter wavelength region due to 4f⁸ → 4f⁷5d¹ transition of Tb³⁺ ions overlapped with 6s² → 6s¹6p¹ (¹S₀ → ³P₁) transition of Bi³⁺ ions and the charge transfer band of Eu³⁺–O^2?. The present phosphors exhibit green and red colors due to ⁵D₄ → ⁷F₅ transition of Tb³⁺ ions and ⁵D₀ → ⁷F₁ transition of Eu³⁺ ions, respectively. The emission was shifted from green to red color by co-doping with Eu³⁺ ions, which indicate that the energy transfer probability from Tb³⁺ to Eu³⁺ ions are dependent strongly on the concentration of Eu³⁺ ions.     

Synthesis and visible-light photocatalysis capability of BiFeO3–(Na0.5Bi0.5)TiO3 nanopowders by a sol–gel method

Multiferroic BiFeO₃–(Na_0.5Bi_0.5)TiO₃ (BFO–NBT) nanopowders were successfully synthesized by a sol–gel method, and the visible-light photocatalytic and magnetic properties of BFO–NBT nanopowders were investigated. X-ray diffraction results indicated that the adding of NBT and the excess of natrium source could suppress the formation of secondary phases and made it easier to obtain single perovskite phase. High photoactivity of this catalyst for Rhodamine B (RhB) degradation under visible-light irradiation was detected, which is due to narrow band gap energy of 2.08 eV, higher surface area and pure phase compounds with no or less amounts of impurities. The BFO–NBT nanopowders showed a weak ferromagnetic order at room temperature, which should be attributed to the size-confinement effects of the nanostructures. It is suggested that BFO–NBT is a kind of new narrow band gap semiconductor visible-light photocatalyst with broad application prospects, in addition to potential applications for novel magnetoelectric devices.     

Thermoelectric properties of the LaCoO3-LaCrO3 system using a high-throughput combinatorial approach

A combinatorial film of the LaCo_1-xCr_xO₃ system was fabricated using the LaCoO₃ and LaCrO₃ targets at the NIST Pulsed Laser Deposition (PLD) facility. As the ionic size of Cr³⁺ is greater than that of Co³⁺, the unit cell volume of the series increases with increasing x. Using a custom screening tool, the Seebeck coefficient of LaCo_1-xCr_xO₃ approaches a measured maximum of 286 μV/K, near to the cobalt-rich end of the film library (with x ≈ 0.49). The resistivity value increases continuously with increasing x. The measured power factor, PF, of this series, which is related to the efficiency of energy conversion, also exhibits a maximum at the composition of x ≈ 0.49, which corresponds to the maximum value of the Seebeck coefficient. Our results illustrate the efficiency of applying the high-throughput combinatorial technique to study thermoelectric materials.     

Structural and electrical properties of (1−x)(Na1/2Bi1/2)TiO3-xPb(Mg1/3Nb2/3)O3 solid solution

Structural, dielectric and piezoelectric properties of (1−x)(Na_1/2Bi_1/2)TiO₃-xPb(Mg_1/3Nb_2/3)O₃ (NBT-xPMN) solid solution have been investigated. An addition of PMN into NBT transformed the structure of sintered samples from rhombohedral to pseudocubic phase where x is larger than 0.1. In calcined powders, however, the intermediate structure were observed between rhombohedral and cubic phases near x=0.1. The formation of solid solution between NBT and PMN modified the dielectric and piezoelectric properties of NBT to be suitable for high temperature dielectric and piezoelectric material. With increasing the content of PMN, the temperature-stability of ε_r(T) increased and the high temperature dielectric loss decreased. In addition, the piezoelectric property of NBT-xPMN was enhanced, for the decrease of coercive field and conductivity promoted the domain reversal under the high electric field of the poling process.     

Structural and magnetic properties of TbxY3−xFe5O12 (0 ≤ x ≤ 0.8) thin film prepared via sol–gel method

Terbium-doped yttrium iron garnet (Tb_xY_3−x Fe₅O₁₂; x = 0.0, 0.2, 0.4, 0.6 and 0.8) nanoparticles thin films have been prepared onto quartz substrate by sol–gel method followed by spin coating process. Annealing of the films was processed at 900 °C in air for 2 h. The structures were investigated by using an X-ray diffractometer (XRD) and a field emission scanning electron microscope (FE-SEM). The magnetic properties were studied by a vibrating sample magnetometer (VSM). The XRD patterns of the films were consistent with a single phase garnet structure. The lattice parameter was initially increased with Tb³⁺ concentration due to the larger size of the Tb³⁺ ion compared to Y³⁺ ion, but a decrease in lattice parameter was observed at higher Tb³⁺ concentration due to the effect of film’s thickness. FE-SEM micrographs reveal that the particles were highly agglomerated. The grain’s sizes for all films were in the range of 40–59 nm. The magnetic measurements at room temperature (25 °C) show that the saturation magnetization (M_s) of the films was reduced with the increase in Tb³⁺ ions, which due to the antiparallel alignment between Tb³⁺ ions and Fe³⁺ ions. The films illustrate normal shapes of hysteresis loops except Tb_0.2Y_2.8Fe₅O₁₂ and Tb_0.4Y_2.6Fe₅O₁₂ films exhibiting two steps increments before being saturated. The coercivity values (H_c) demonstrate non linear dependency with the terbium concentration (x).     

Structure and spectroscopic properties of (Y,Eu)(PO3)3 polyphosphate red phosphors

A series of orange-red emitting phosphor Y(PO₃)₃: xEu³⁺ (x = 0.1–1.0) was prepared by a solid-state reaction route. The phosphors were characterized by X-ray diffraction (XRD) and photoluminescence (PL) as well as decay lifetimes. Studies revealed the phase transfer from monoclinic to orthorhombic when Y³⁺ is totally replaced by Eu³⁺, and expansion of the unit cell occurs with increasing Eu³⁺ doped content. The PL spectra show that the phosphors Y(PO₃)₃: xEu³⁺ can be effectively excited by near ultraviolet (n-UV) light, and exhibit strong red-orange emission with no concentration quenching. The profile of PL spectra changes significantly at high Eu³⁺ content (x ≥ 0.80), which is due to the variation of preference for substitution of Eu³⁺. The luminescence due to the ⁵D₀ → ⁷F_J (J = 1, 2) transitions at 77 K exhibits its own spectral features for different crystallographic site. It is found that Eu³⁺ ions occupy the centers of octahedral polyhedron and form C_i/C₁ point group in Y(PO₃)₃.     

Enhanced energy-storage performance and thermal stability in Bi0.5Na0.5TiO3-based ceramics through defect engineering and composition design

Dielectric ceramics have been widely used in advanced microelectronics systems due to their inherent rapid charging/discharging capabilities and superb power density. However, concurrently attaining high energy storage density (W_rec), superior efficiency (η), and excellent thermal stability are arduous tasks for actual applications in dielectric ceramics. Herein, the introduction of predictable defects A-site vacancies (V_A) and oxygen vacancies (V_O) into the morphotropic phase boundary (MPB) of (Bi_0.45La_0.05Na_0.5)_0.94Ba_0.06TiO₃ (BLNBT) ceramics leads to a pinning effect in the grain boundary to improve the breakdown strength and energy storage performance. According to this strategy, the novel Sr_0.8Bi_0.1□_0.1Ti_0.8Zr_0.2O_2.95 (SBTZ)-modified BLNBT ceramics are designed and manufactured, which include SBTZ with a high relaxation behavior gene and BLNBT with an inherently high maximum polarization gene. As a result, a large W_rec of 3.84 J/cm³ with an excellent η of 90.8%, and outstanding charge/discharge capabilities (C_D ～ 584.99 A/cm², P_D ～ 40.94 MW/cm³ and τ_0.9 ～ 95 ns) in the 0.75BLNBT-0.25SBTZ ceramic are achieved. Notably, the corresponding ceramic shows a slight degradation of W_rec with a variation of less than 8% (RT ～ 200 °C), while the η remains at over 90%. The predictable defect engineering strategy proposed in this work is an effective way to develop new Bi_0.5Na_0.5TiO₃-based systems with good energy storage performances.     

LiBa0.95-yBO3∶0.05Tb3+,yBi3+荧光粉的制备及荧光性质

以硼酸和碳酸盐为原料,用高温固相法制备了可被(近)紫外光(369、254 nm)有效激发的Tb³⁺单掺杂Li Ba1-xBO3∶xTb³⁺(物质的量分数x=0.02、0.03、0.04、0.05、0.06、0.07)及Bi³⁺和Tb³⁺共掺杂LiBa_0.95-yBO₃∶0.05Tb³⁺,y Bi³⁺(物质的量分数y=0.02、0.03、0.04、0.05、0.06、0.07)的2个系列荧光粉,产物的结构和形貌分别用粉末X射线衍射(PXRD)和扫描电子显微镜进行表征。PXRD测定结果表明2个系列的产物均为纯相LiBaBO3。通过对第一系列产物荧光光谱的测定,筛选出发光强度最好的产物,据此确定铽离子的最佳掺杂量;在此基础上制备出铋离子掺杂量不同的第二系列荧光粉。荧光光谱测定的实验结果表明,Tb³⁺/Bi³⁺共掺杂的荧光粉的发光强度好于Tb³⁺单掺杂的荧光粉,这说明Bi³⁺对Tb³⁺有敏化作用;而且随着Bi³⁺掺杂量的增加,产物的荧光强度表现出先增加后减小的趋势,当Bi³⁺的掺杂量y=0.03时,产物的荧光强度达到最大。Bi³⁺和Tb³⁺之间存在偶极-四极相互作用而进行能量传递。系列荧光粉的CIE坐标显示其发光颜色在一定程度上呈现出由绿色光到白光的渐变趋势。     

Mono- and Mixed Metal Complexes of Eu3+, Gd3+, and Tb3+ with a Diketone,Bearing Pyrazole Moiety and CHF2-Group: Structure,Color Tuning,and Kinetics of Energy Transfer between Lanthanide Ions

Three novel lanthanide complexes with the ligand 4,4-difluoro-1-(1,5-dimethyl-1H-pyrazol-4-yl)butane-1,3-dione (HL), namely [LnL₃(H₂O)₂], Ln = Eu, Gd and Tb, were synthesized, and, according to single-crystal X-ray diffraction, are isostructural. The photoluminescent properties of these compounds, as well as of three series of mixed metal complexes [Eu_xTb_1-xL₃(H₂O)₂] (Eu_xTb_1-xL₃), [EuxGd_1-xL₃(H₂O)₂] (Eu_xGd_1-xL₃), and [Gd_xTb_1-xL₃(H₂O)₂] (Gd_xTb_1-xL₃), were studied. The Eu_xTb_1-xL₃ complexes exhibit the simultaneous emission of both Eu³⁺ and Tb³⁺ ions, and the luminescence color rapidly changes from green to red upon introducing even a small fraction of Eu³⁺. A detailed analysis of the luminescence decay made it possible to determine the observed radiative lifetimes of Tb³⁺ and Eu³⁺ and estimate the rate of excitation energy transfer between these ions. For this task, a simple approximation function was proposed. The values of the energy transfer rates determined independently from the luminescence decays of terbium(III) and europium(III) ions show a good correlation.     

Structural and Spectroscopic Effects of Li+ Substitution for Na+ in LixNa1-xCaGd0.5Ho0.05Yb0.45(MoO4)3 Scheelite-Type Upconversion Phosphors

A set of new triple molybdates, Li_xNa_1-xCaGd_0.5(MoO₄)₃:Ho³⁺_0.05/Yb³⁺_0.45, was successfully manufactured by the microwave-accompanied sol–gel-based process (MAS). Yellow molybdate phosphors Li_xNa_1-xCaGd_0.5(MoO₄)₃:Ho³⁺_0.05/Yb³⁺_0.45 with variation of the Li_xNa_1-x (x = 0, 0.05, 0.1, 0.2, 0.3) ratio under constant doping amounts of Ho³⁺ = 0.05 and Yb³⁺ = 0.45 were obtained, and the effect of Li⁺ on their spectroscopic features was investigated. The crystal structures of Li_xNa_1-xCaGd_0.5(MoO₄)₃:Ho³⁺_0.05/Yb³⁺_0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) at room temperature were determined in space group I4₁/a by Rietveld analysis. Pure NaCaGd_0.5Ho_0.05Yb_0.45(MoO₄)₃ has a scheelite-type structure with cell parameters a = 5.2077 (2) and c = 11.3657 (5) Å, V = 308.24 (3) ų, Z = 4. In Li-doped samples, big cation sites are occupied by a mixture of (Li,Na,Gd,Ho,Yb) ions, and this provides a linear cell volume decrease with increasing Li doping level. The evaluated upconversion (UC) behavior and Raman spectroscopic results of the phosphors are discussed in detail. Under excitation at 980 nm, the phosphors provide yellow color emission based on the ⁵S₂/⁵F₄ → ⁵I₈ green emission and the ⁵F₅ → ⁵I₈ red emission. The incorporated Li⁺ ions gave rise to local symmetry distortion (LSD) around the cations in the substituted crystalline structure by the Ho³⁺ and Yb³⁺ ions, and they further affected the UC transition probabilities in triple molybdates Li_xNa_1-xCaGd_0.5(MoO₄)₃:Ho³⁺_0.05/Yb³⁺_0.45. The complex UC intensity dependence on the Li content is explained by the specificity of unit cell distortion in a disordered large ion system within the scheelite crystal structure. The Raman spectra of Li_xNa_1-xCaGd_0.5(MoO₄)₃ doped with Ho³⁺ and Yb³⁺ ions were totally superimposed with the luminescence signal of Ho³⁺ ions in the range of Mo–O stretching vibrations, and increasing the Li⁺ content resulted in a change in the Ho³⁺ multiplet intensity. The individual chromaticity points (ICP) for the LiNaCaGd(MoO₄)₃:Ho³⁺,Yb³⁺ phosphors correspond to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates.     

Significantly Improved Colossal Dielectric Properties and Maxwell—Wagner Relaxation of TiO2—Rich Na1/2Y1/2Cu3Ti4+xO12 Ceramics

In this work, the colossal dielectric properties and Maxwell—Wagner relaxation of TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ (x = 0–0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na_1/2Y_1/2Cu₃Ti₄O₁₂ is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (R_gb). The colossal permittivities of ε′ ~ 0.7–1.4 × 10⁴ with slightly dependent on frequency in the frequency range of 10²–10⁶ Hz are obtained in the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016–0.020 at 1 kHz due to the increased R_gb. The semiconducting grain resistance (R_g) of the Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics increases with increasing x, corresponding to the decrease in Cu⁺/Cu²⁺ ratio. The nonlinear electrical properties of the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics are explained by the Maxwell–Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.     

Preparation of (1? x %)(Na0.5Bi0.5)TiO3– x %SrTiO3 thin films by a sol–gel method for dielectric tunable applications

(1−x%)(Na_0.5Bi_0.5)TiO₃–x%SrTiO₃ (NBTSx) thin films were deposited on Pt/TiO₂/SiO₂/Si substrates by a spin-on sol–gel method and rapid thermal annealing. The stock solutions were prepared using sodium acetate, bismuth acetate, strontium acetate, and titanium n-butoxide as precursors, ethanol, and acetic acid as solvents and acetylacetone as the chelating agent. The thermal treatment conditions were determined by thermal analyses of the dry gel powders derived from the stock solutions. Structure and dielectric tunable properties of the films were studied as functions of Sr concentration. NBTSx films exhibit the perovskite structure of a pseudo-cubic symmetry with the lattice parameters increasing with increasing Sr concentration. It was found that the substitution of Sr in Na_0.5Bi_0.5TiO₃ may greatly reduce the dielectric loss while decrease the tunability at the same time. The best figure of merit was achieved in NBTS80 films. The results were discussed and compared with related materials.     

Warm white light from Y4MgSi3O13:Bi, Eu nanophosphor for white light-emitting diodes

Y₄MgSi₃O₁₃:Bi³⁺, Eu³⁺ nanophosphors have been prepared by a facile sol–gel method. The products have been characterized by X-ray diffraction, field-emission scanning electron microscopy and fluorescence measurements. The results show that the nanophosphors are of single phase hexagonal Y₄MgSi₃O₁₃ with size-distribution of 50–90 nm in diameter. White-light emission has been obtained from Bi³⁺ and Eu³⁺ co-doped Y₄MgSi₃O₁₃ nanophosphors upon excitation of 350 nm ultraviolet light. It is noted that Bi³⁺ ions can occupy two different Y³⁺ sites and generate different emissions from the ³p₁ → ¹s₀ transition. Warm white light has been obtained from Y₄MgSi₃O₁₃:Bi³⁺, Eu³⁺ nanophosphors according to Commission International de I’Eclairage (CIE) chromaticity coordinates and color temperature (T_c) with appropriately adjusted contents of Bi³⁺ and Eu³⁺. The results indicate that Y₄MgSi₃O₁₃:0.08Bi³⁺, 0.04Eu³⁺ (x = 0.31, y = 0.31, T_c = 6907 K) are potential nanophosphors for white light-emitting diodes (LEDs) applications.     

Synthesis of New LnxBi2–xSe3 (Ln: Sm3+, Eu3+, Gd3+, Tb3+) Nanomaterials and Investigation of Their Optical Properties

New Ln_xBi_2–xSe₃ (Ln: Sm³⁺, Eu³⁺, Gd³⁺, Tb³⁺) based nanomaterials were synthesized by a co‐reduction method. Powder XRD patterns indicate that the Ln_xBi_2–xSe₃ crystals (Ln = Sm³⁺, Eu³⁺, x = 0.00–0.44 and Ln = Gd³⁺, Tb³⁺, x = 0.00–0.50) are isostructural with Bi₂Se₃. The cell parameter c decreases for Ln = Eu³⁺, Gd³⁺, Tb³⁺ upon increasing the dopant content (x), while a slightly increases. Changes in lattice parameters could be related to the radii of cations. SEM images show that doping of the lanthanide ions in the lattice of Bi₂Se₃ generally results in nanoflowers. For the terbium compound two kinds of morphologies (nanoflowers and nanobelts) were observed. UV/Vis absorption and emission spectroscopy reveals mainly electronic transitions of the Ln³⁺ ions. Emission spectra show intense transitions from the excited to the ground state of Ln³⁺ and energy transfer from the Bi₂Se₃ lattice. Emission spectra of europium‐doped materials, in addition to the characteristic red emission peaks of Eu³⁺, show an intense blue emission band centered at 432 nm, originating from the 4f⁶5d¹ to 4f⁷ configuration in Eu²⁺. EPR measurements confirm the existence of Eu²⁺ in the materials. Interestingly, for all samples starting at low Ln³⁺ concentration, the emission intensity rises to a maximum at a Ln³⁺ concentration of x = 0.2 and falls again steadily to a minimum at x = 0.45.     

Fabrication and properties of xBiFeO3-(1 − x)Bi4Ti3O12 system by sol–gel process

The thin films of mixture of xBiFeO₃-(1 − x)Bi₄Ti₃O₁₂ (x = 0.4, 0.5, and 0.6) system were prepared by a sol–gel process. The thicknesses of the thin films were 540, 500, and 570 nm, respectively. The crystal structure of all thin films annealed at 650 °C was analyzed by X-ray diffraction. It was found that the thin films at x = 0.4 and 0.5 mainly consisted of a Bi₄Ti₃O₁₂ phase while Bi₅Ti₃FeO₁₅ was the major phase of the thin film at x = 0.6. The thin film (x = 0.6) showed better ferroelectric properties in remnant polarization and polarization fatigue than those observed in the thin films (x = 0.4 and 0.5). The values of remnant polarization 2P _r and coercive field 2E c of the thin film at x = 0.6 were 36 μC/cm² and 192 kV/cm at an applied electric field of 260 kV/cm, respectively. There was almost no polarization fatigue up to 10¹⁰ switching cycles. Also weak ferromagnetism was observed in the thin film at x = 0.6.