Enhanced magnetoelectric coupling in La-modified Bi<Subscript>5</Subscript>Co<Subscript>0.5</Subscript>Fe<Subscript>0.5</Subscript>Ti<Subscript>3</Subscript>O<Subscript>15</Subscript> multiferroic ceramics

Multiferroic properties of La-modified four-layered perovskite Bi_5?x La _x Fe_0.5Co_0.5Ti₃O₁₅ (0 ≤ x ≤ 1) ceramics were investigated, by analyzing the magnetodielectric effect, magneto-polarization response and magnetoelectric conversion. X-ray diffraction indicated the formation of pure Aurivillius ceramics, and Raman spectroscopy revealed the Bi ions displacement and the crystal structure variation. The enhancement of ferromagnetic and ferroelectric properties was observed in Bi_5?x La _x Fe_0.5Co_0.5Ti₃O₁₅ after La modification. The evidence for enhanced ME coupling was determined by magnetic field-induced marked variations in the dielectric constant and polarization. A maximum ME coefficient of 1.15 mV/cm·Oe was achieved in Bi_4.25La_0.75Fe_0.5Co_0.5Ti₃O₁₅ ceramic, which provides the possible promise for novel magnetoelectric device application.     

Effect of Bi and Sr doping on morphological and magnetic properties of LaCo<Subscript>0.6</Subscript>Fe<Subscript>0.4</Subscript>O<Subscript>3</Subscript> nanosized perovskites

Nanopowders of La _1?x Bi _x Co_0.6Fe_0.4O₃ (x = 0, 0.1, 0.2) and La _1?2x Bi _x Sr _x Co_0.6Fe_0.4O₃ (x = 0.1) multinary perovskites were synthesized by citrate sol–gel autocombustion method. Crystalline phase and the lattice parameters were obtained from X-ray diffraction pattern. The XRD result shows that all compounds have rhombhohedral crystal structure with \(\bar {\mathbf {R}\mathbf {3}}\)c space group and Bi (x = 0.2) have the presence of secondary peaks. Crystallite size, dislocation density, specific area and strain were calculated from XRD. The elemental composition and micrographs of grain were obtained from EDAX (energy dispersive X-ray analysis) and SEM (scanning electron microscopy), with an average grain size below 400 nm. Surface morphological studies using XPS (X-ray photoelectron spectroscopy) were used to find out the chemical states and surface proportion of oxygen present in samples. Finally, using the vibrating sample magnetometer the room temperature magnetic behaviour of compounds was studied and it was observed that the ferromagnetic behaviour of LaCo_0.6Fe_0.4O₃ was reduced by Bi and Sr doping.     

Magnetic properties of LaInO<Subscript>3</Subscript>-based perovskite-structure photoluminescent materials doped with Nd<Superscript>3+</Superscript>, Cr<Superscript>3+</Superscript>, and Mn<Superscript>3+</Superscript> ions

Single-phase ceramic samples of La_1–xNd_xInO₃ (0.007 ≤ x ≤ 0.05), LaIn_0.99M_0.01O₃, and La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺) solid solutions have been prepared by solid-state reactions, and their crystal structure, magnetic field dependences of their specific magnetization at 5 and 300 K, and temperature dependences of their molar magnetic susceptibility have been studied. It has been shown that the 300-K specific magnetization of the La_1–xNd_xInO₃ (x = 0.02, 0.05), La_0.95Nd_0.05In_0.995M_0.005O₃ (M = Cr³⁺ and Mn³⁺), and LaIn_0.99Mn_0.01O₃ solid solutions increases linearly with increasing magnetic field strength up to 14 T and that the magnitude of the 300-K specific magnetization of the La_0.993Nd_0.007InO₃ and LaIn_0.99Cr_0.01O₃ solid solutions increases linearly, but they have diamagnetic magnetization. At a temperature of 5 K, the magnetization of all the indates studied here increases nonlinearly with increasing magnetic field strength, gradually approaching magnetic saturation, without, however, reaching it in a magnetic field of 14 T. In the temperature range where the Curie–Weiss law is obeyed (5–30 K), the effective magnetic moments obtained for the Nd³⁺ ion (\({\mu _{effN{d^{3 + }}}}\)) in the La_1–xNd_xInO₃ solid solutions with x = 0.007, 0.02, and 0.05 are 2.95μ_B, 3.09μ_B, and 2.75μ_B, respectively, which is well below the theoretical value \({\mu _{effN{d^{3 + }}}}\)= 3.62μ_B. The effective magnetic moments of the Cr³⁺ and Mn³⁺ ions in the LaIn_0.99Cr_0.01O₃ and LaIn_0.99Mn_0.01O₃ solid solutions are 3.87μ^B and 5.11μ^B, respectively, and differ only slightly from the theoretical values \({\mu _{effC{r^{3 + }}}}\)= 3.87μ^B and \({\mu _{effM{n^{3 + }}}}\)= 4.9μ^B.     

Magnetic and ferroelectric properties of SmBi<Subscript>4</Subscript>Fe<Subscript>0.5</Subscript>Co<Subscript>0.5</Subscript>Ti<Subscript>3</Subscript>O<Subscript>15</Subscript> compounds prepared with different synthesis methods

The SmBi₄Fe_0.5Co_0.5Ti₃O₁₅ compounds were prepared by the insertion of the SmFe_0.5Co_0.5O₃ into the Bi₄Ti₃O₁₂ host and the conventional solid state reaction method, respectively. X-ray diffraction analysis indicates that the conventional solid state reaction method favors the formation of a single phase four-layer Aurivillius phase of SmBi₄Fe_0.5Co_0.5Ti₃O₁₅ more easily than that prepared by the insertion method. Magnetic and ferroelectric measurements demonstrate that the samples prepared by both methods exhibit coexistence of strong ferromagnetic and weak ferroelectric behaviors at room temperature. Compared with the Bi₅FeTi₃O₁₅, the ferromagnetism of the SmBi₄Fe_0.5Co_0.5Ti₃O₁₅ was dramatically enhanced by the partial substitution of Co for Fe and Sm for Bi. The SmBi₄Fe_0.5Co_0.5Ti₃O₁₅ samples exhibit large magnetic responses (2M _r ?~?643 memu/g and coercive fields 2H _c ?~?344 Oe) at room temperature.     

Fluorination of Bi<Subscript>1.8</Subscript>Fe<Subscript>1.2</Subscript>SbO<Subscript>7</Subscript> pyrochlore solid solutions

A technique has been developed for fluorinating the pyrochlore oxide Bi_1.8Fe_0.2FeSbO₇, and a compound with the composition Bi_1.8Fe_1.2SbO_7–x/2F_x has been obtained. The synthesized oxyfluoride also has the pyrochlore structure (sp. gr. Fd3m), with a lattice parameter a = 10.4443(1) Å (R _wp = 5.2). It has been shown that the charge balance upon fluorine substitution for oxygen is maintained not through partial reduction of Fe³⁺ to Fe²⁺ but through the incorporation of fluorine into oxygen vacancies. The magnetic behavior of the fluorinated pyrochlore phase is determined by the persisting frustration of the octahedral sublattice, which is responsible for the development of a spin glass state below T _f = 12 K. The fluorination-induced changes in the anion sublattice led to an increase in the antiferromagnetic exchange interaction between neighboring Fe³⁺ ions and changes in the dynamic properties of the spin glass phase.     

Improvement of the Magnetization of Barium Hexaferrites Induced by Substitution of Nd<Superscript>3+</Superscript> Ions for Fe<Superscript>3+</Superscript> Ions

Barium hexagonal ferrites (BaNd _x Fe_12?x O ₁₉) have been synthesized by initial high-energy milling of the precursors and calcining subsequently. The as-prepared samples are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometry (VSM). XRD and SEM examinations reveal that a high-crystallized hexagonal BaNd _x Fe_12?x O ₁₉ with lamellar morphology is obtained when the precursor is calcined at 1200^°C in air for 3 h. The hexagonal crystalline structure of BaFe₁₂ O ₁₉ is not changed after doping Nd³⁺ ions in BaFe₁₂ O ₁₉. However, lattice parameters a and b values increase with an increase in Nd content at first, then decrease. Nd substitution may improve the magnetic properties of BaNd _x Fe_12?x O ₁₉. BaNd_0.1Fe_11.9 O ₁₉, obtained at 1050^°C, has the highest specific saturation magnetization value (80.81 emu/g) and magnetic moment (16.21 μ _B); BaNd_0.2Fe_11.8 O ₁₉, obtained at 950^°C, has the highest coercivity value, 4075.19 Oe.     

Strong up-conversion luminescence and electrical properties of SrBi<Subscript>4</Subscript>Ti<Subscript>4</Subscript>O<Subscript>15</Subscript> multifunctional ceramics by Er<Superscript>3+</Superscript> doping

Novel green-emitting piezoelectric ceramics of SrBi_4?x Er _x Ti₄O₁₅ (SBT-xEr) were prepared. Strong up-conversion with bright green (524 and 548 nm) and a relatively weak red (660 nm) emission bands were obtained under 980 nm excitation at room temperature, which is attributed to the intra 4f–4f electronic transition of (²H_11/2, ⁴S_3/2)–⁴I_15/2 and the transition from ⁴F_9/2 to ⁴I_15/2 of Er³⁺ ions, respectively. Simultaneously, Er³⁺ doping promotes the electrical properties. At 0.8 mol%Er, the optimal electric properties with high Curie temperature of T _c?~527?°C, large remanent polarization of 2P _r?~14.92 μC/cm² and piezoelectric constant of d ₃₃?~17 pC/N was achieved. As a multifunctional material, Er³⁺ doped SBT showed a great potential to be used in 3D-display, bio-imaging, solid state laser and optical temperature sensor.     

Diffusion phase transition and impedance spectroscopy of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>/CuO co-doped BCZT lead-free ceramics

Perovskite type (Ba_0.85Ca_0.15?2x Bi_2x )(Zr_0.1Ti_0.9?x Cu _x )O₃ lead-free ceramics were prepared via a conventional solid-state reaction method. The phase structure, dielectric, ferroelectric properties and complex impedance were investigated in detail. XRD and dielectric measurements determined that single orthorhombic phase displayed in (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ at room temperature. With the introduction of Bi₂O₃/CuO, the phase structure exhibited the mixture of orthorhombic and tetragonal phases, and then turned to single tetragonal phase. In contrast to the sharp dielectric transition of (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ ceramics, a broad dielectric peak coupled with a slight decrease in Curie temperature was observed in (Ba_0.85Ca_0.15?2x Bi_2x )(Zr_0.1Ti_0.9?x Cu _x )O₃ ceramics with increasing x. The observed diffuse phase transition behavior was further confirmed by a couple of measurements with polarization loops and polarization current density curves. The structural and the composition fluctuations induced by ions doping should be responsible for the diffuse phase transition behavior. Furthermore, physical mechanisms of the conduction and relaxation processes were revealed by using impedance spectroscopy analyses. It was concluded that the conduction and relaxation processes were thermally activated, which was closely linked with the singly and doubly ionized oxygen vacancies.     

Electrical conductivity of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-Tm<Subscript>2</Subscript>O<Subscript>3</Subscript>-Nb<Subscript>2</Subscript>O<Subscript>5</Subscript> solid solutions

New solid solutions, Bi_2?x?y Tm _x Nb _y O_3+δ, with tetragonal and cubic structures have been synthesized in the Bi₂O₃-Tm₂O₃-Nb₂O₅ system, and their electrical conductivity has been measured at temperatures from 670 to 1020 K. The 1020-K conductivity of the tetragonal solid solution Bi_1.8Tm_0.15Nb_0.05O_3+δ is comparable to that of Bi_1.75Tm_0.25O₃, the best conductor in the Bi₂O₃-Tm₂O₃ system.     

Very high thermal stability with excellent dielectric,and non-ohmics properties of Mg-doped CaCu<Subscript>3</Subscript>Ti<Subscript>4.2</Subscript>O<Subscript>12</Subscript> ceramics

In this work, the nominal CaCu_3?xMg_xTi_4.2O₁₂ (0.00, 0.05 and 0.10) ceramics were prepared by sintering pellets of their precursor powders obtained by a polymer pyrolysis solution method at 1100 °C for different sintering time of 8 and 12 h. Very low loss tangent (tanδ)?<?0.009–0.014 and giant dielectric constant (ε′) ～?1.1?×?10⁴–1.8?×?10⁴ with excellent temperature coefficient (Δε′) less than ±?15% in a temperature range of ??60 to 210 °C were achieved. These excellent performances suggested a potent application of the ceramics for high temperature X8R and X9R capacitors. It was found that tanδ values decreased with increasing Mg²⁺ dopants due to the increase of grain boundary resistance (R_gb) caused by the very high density of grain, resulting from the substitution of small ionic radius Mg²⁺ dopants in the structure. In addition, CaCu_3?xMg_xTi_4.2O₁₂ ceramics displayed non-linear characteristics with the significant enhancements of a non-linear coefficient (α) and a breakdown field (E_b) due to Mg²⁺doping. The high values of ε′ (14012), α (13.64) and E_b (5977.02 V/cm) with very low tanδ value (0.009) were obtained in a CaCu_2.90Mg_0.10Ti_4.2O₁₂ ceramic sintered at 1100 °C for 8 h.     

Cu<Superscript>2+</Superscript> and Al<Superscript>3+</Superscript> co-substituted cobalt ferrite: structural analysis,morphology and magnetic properties

Cu–Al substituted Co ferrite nanopowders, Co_1?x Cu _x Fe_2?x Al _x O₄ (0.0 ≤ x ≤ 0.8) were synthesized by the co-precipitation method. The effect of Cu–Al substitution on the structural and magnetic properties have been investigated. X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, field emission scanning electron microscopy (FESEM) and vibrating sample magnetometer (VSM) are used for studying the effect of variation in the Cu–Al substitution and its impact on particle size, magnetic properties such as M _s and H _c . Cu–Al substitution occurs and produce a secondary phase, α-Fe ₂ O ₃. The crystallite size of the powder calcined at 800 ^°C was in the range of 19–26 nm. The lattice parameter decreases with increasing Cu–Al content. The nanostructural features were examined by FESEM images. Infrared absorption (IR) spectra shows two vibrational bands; at around 600 (v ₁) and 400 cm ^?1 (v ₂). They are attributed to the tetrahedral and octahedral group complexes of the spinel lattice, respectively. It was found that the physical and magnetic properties have changed with Cu–Al contents. The saturation magnetization decreases with the increase in Cu–Al substitution. The reduction of coercive force, saturation magnetization and magnetic moments are may be due to dilution of the magnetic interaction.     

Synthesis and luminescence properties of LiBaPO<Subscript>4</Subscript>:Bi<Superscript>3+</Superscript> yellow-emitting phosphor for solid-state lighting

Novel LiBaPO₄:Bi³⁺ yellow-emitting phosphor is synthesized by high temperature solid-state reaction method in air. With excitation 260 nm, LiBaPO₄:Bi³⁺ phosphor emits yellow light with the chromaticity coordinate (0.4272, 0.4657) and color rendering index 77.7. Emission band peaking at ~?588 nm of LiBaPO₄:Bi³⁺ phosphor in the range of 400–790 nm is attributed to the ³P₁ → ¹S₀ electron transition of Bi³⁺ ion. Excitation band monitored at 588 nm in the range of 220–300 nm is assigned to the ¹S₀ → ³P₁ electron transition of Bi³⁺ ion. The optimal Bi³⁺ ion concentration in LiBaPO₄:Bi³⁺ phosphor is ~?1.0 mol%. Time resolved spectra and fluorescence lifetime data confirm that there is only Bi³⁺ ion luminous center in LiBaPO₄:Bi³⁺ phosphor. The luminous mechanism is analyzed by configurational coordinate diagram of Bi³⁺ ion. The experiment results are helpful to develop other new Bi³⁺-doped optical materials for solid-state lighting.     

The magnetic properties of BiY<Subscript>2</Subscript>Fe<Subscript>5</Subscript>O<Subscript>12</Subscript> nanoparticles doped with Cr ions

BiY₂Cr _x Fe_5?x O₁₂ (x = 0, 0.05, 0.1, 0.2, 0.3) nanocrystals were synthesized by using a sol-gel method. Samples were characterized by the powder X-ray diffraction (XRD), the thermal gravity analysis (TGA) and the differential thermal analysis (DTA), the vibrating sample magnetometer(VSM) and Mössbauer spectrums. The average sizes of the particles were determined by the Scherrer’s formula. The special Ms and Mössbauer spectra of BiY₂Cr _x Fe_5?x O₁₂ nanocrystals are researched at room temperature. It is seen that the special Mss of samples are initially increased with increasing Cr³⁺ content (x < 0.1), and decreased with increasing content of Cr³⁺ ions (x > 0.1).     

Effects of Ge<Superscript>4+</Superscript> acceptor dopant on sintering and electrical properties of (K<Subscript>0.5</Subscript>Na<Subscript>0.5</Subscript>)NbO<Subscript>3</Subscript> lead-free piezoceramics

Lead-free (K_0.5Na_0.5)(Nb_1-xGe _x )O₃ (KNN-xGe, where x = 0-0.01) piezoelectric ceramics were prepared by conventional ceramic processing. The effects of Ge⁴⁺ cation doping on the phase compositions, microstructure and electrical properties of KNN ceramics were studied. SEM images show that Ge⁴⁺ cation doping improved the sintering and promoted the grain growth of the KNN ceramics. Dielectric and ferroelectric measurements proved that Ge⁴⁺ cations substituted Nb⁵⁺ ions as acceptors, and the Curie temperature (T_C) shows an almost linear decrease with increasing the Ge⁴⁺ content. Combining this result with microstructure observations and electrical measurements, it is concluded that the optimal sintering temperature for KNN-xGe ceramics was 1020°C. Ge⁴⁺ doping less than 0.4 mol.%can improve the compositional homogeneity and piezoelectric properties of KNN ceramics. The KNN-xGe ceramics with x = 0.2% exhibited the best piezoelectric properties: piezoelectric constant d₃₃ = 120 pC/N, planar electromechanical coupling coefficient k_p = 34.7%, mechanical quality factor Q_m = 130, and tanδ = 3.6%.     

New,thermally stable Gd<Subscript>11</Subscript>(GeO<Subscript>4</Subscript>)(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>O<Subscript>10</Subscript>-based upconversion phosphors

A series of Gd_11–x–y Yb _x Er _y GeP₃O₂₆ germanate phosphates differing in the ratio of the Yb³⁺ and Er³⁺ active ions have been synthesized, and their luminescence spectra have been measured. According to X-ray diffraction characterization results, all of the synthesized germanate phosphates are single-phase and have a triclinic structure (sp. gr. P1). We have measured upconversion luminescence spectra due to the Er^{3+ 2}H_11/2, ⁴S_3/2 → ⁴I_15/2 and ⁴F_9/2 → ⁴I_15/2 radiative transitions in the synthesized gadolinium ytterbium erbium germanate phosphates and determined the luminescence upconversion energy yield (B _en) in Gd_11–x–y Yb _x Er _y GeP₃O₂₆. The effects of the concentrations and ratio of the dopants in the Gd₁₁(GeO₄)(PO₄)₃O₁₀ germanate phosphate host on B _en and the ratio of the luminescence intensities in the red and green spectral regions (R/G) have been assessed.     

Perovskite M<Superscript>I</Superscript>M<Superscript>II</Superscript>O<Subscript>3</Subscript> as a matrix for incorporation of the actinide fraction of HLW

Perovskites of the compositions xLa₂O₃·Al₂O₃ and xLa₂O₃·Fe₂O₃ were prepared by cold pressing and sintering at temperatures of up to 1500°C, and their properties were studied. Perovskites based on lanthanum aluminate are more porous than those based on lanthanum ferrite, whereas the rate of radionuclide leaching from the former compounds is lower than from the latter compounds. The parameter x varied in a relatively wide range does not affect the leaching rate.     

Critical Behavior of La<Subscript>0.67</Subscript>Ba<Subscript>0.33</Subscript>Mn<Subscript>0.95</Subscript>Fe<Subscript>0.05</Subscript>O<Subscript>3</Subscript> Manganite

The critical behavior of perovskite manganite La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ at the ferromagnetic–paramagnetic has been analyzed. The results show that the sample exhibited the second-order magnetic phase transition. The estimated critical exponents derived from the magnetic data using various such as modified d’Arrott plot Kouvel–Fisher method and critical magnetization M(T _C, H). The critical exponents values for the La_0.67Ba_0.33Mn_0.95Fe_0.05O₃ are close to those expected from the mean field model β = 0.504 ± 0.01 with T _C = 275661 ± 0.447 (from the temperature dependence of the spontaneous magnetization below T _C ), γ = 1.013 ± 0.017 with T _C = 276132 ± 0.452 (from the temperature dependence of the inverse initial susceptibility above T _C ), and δ = 3.0403 ± 0.0003. Moreover, the critical exponents also obey the single scaling equation of M(H, ε) = |ε| ^β f _±(H/|ε| ^β+γ ).     

Upconversion Luminescence of Gd<Subscript>2</Subscript>O<Subscript>3</Subscript> Nanocrystals Doped with Er<Superscript>3+</Superscript> and Yb<Superscript>3+</Superscript> Ions

The upconversion luminescence (UCL) of nanocrystalline gadolinium oxide (Gd₂O₃) doped with Er³⁺ and Yb³⁺ ions has been studied in the temperature range of 90–400 K. The nanocrystals were synthesized by chemical vapor deposition and possessed a cubic crystalline structure with an average particle size within 48–57 nm. It is established that the USL intensity in the red (⁴F_9/2 → ⁴I_15/2 transition in Er3+ ion) and green (⁴S_3/2 → ⁴I_15/2 transition) spectral regions depends on the sample temperature and concentration of dopant ions, as well as on the additional structural defects (anion vacancies) created in the crystal lattice by the introduction of Zn²⁺ ions or irradiation with high-energy (10 MeV) electrons. The luminescence efficiency and spectrum of the upconversion phosphor are determined by energy transfer processes.     

Ionic conductivity of BaF<Subscript>2</Subscript> + ZnF<Subscript>2</Subscript> + CdF<Subscript>2</Subscript> + YbF<Subscript>3</Subscript> optical fluoride ceramic

The electrical conductivity of an optical fluoride ceramic in the quaternary system BaF₂ + ZnF₂ + CdF₂ + YbF₃ has been determined in the temperature range 338–722 K using impedance spectroscopy (5 to 5 × 10⁵ Hz). The 500-K ionic conductivity of the ceramic is σ = 3.3 × 10^–4 S/cm, which corresponds to the electrical characteristics of single crystals of the best conducting nonstoichiometric M_1–x R _x F_{2 + x} (M = Sr, Ba; R = La–Nd; x = 0.3–0.5) fluorite phases. We have observed nonmonotonic variation (breaks) in temperature-dependent σ, which is due to competing fluoride ion transport processes in different parts of the ceramic sample. The highly conductive state of the BaF₂ + ZnF₂ + CdF₂ + YbF₃ fluoride ceramic seems to be due to the formation of structural regions corresponding to a Ba_1–x Yb _x F_{2 + x} solid solution.     

New NaSrPO<Subscript>4</Subscript>:Sm<Superscript>3+</Superscript> phosphor as orange-red emitting material

Sm³⁺-activated NaSrPO₄ phosphors could be efficiently excited at 403 nm, and exhibited a bright red emission mainly including four wavelength peaks of 565, 600, 646 and 710 nm. The highest emission intensity was found for NaSr _1?x PO₄: xSm³⁺ with a composition of x = 0.007. Concentration quenching was observed as the composition of x exceeds 0.007. The decay time values of NaSr_1?x PO ₄ : xSm³⁺ phosphors range from around 2.55 to 3.49 ms. NaSr_1?x PO₄: xSm³⁺ phosphor shows a higher thermally stable luminescence and its thermal quenching temperature T ₅₀ was found to be 350°C, which is higher than that of commercial YAG:Ce³⁺ phosphor and ZnS:(Al, Ag) phosphor. Because NaSr_1?x PO₄: xSm³⁺ phosphor features a high colour-rendering index and chemical stability, it is potentially useful as a new scintillation material for white light-emitting diodes.