Effect of Dy-substitution on structural,electrical and magnetic properties of multiferroic BiFeO3 ceramics

The polycrystalline samples of dysprosium (Dy)-modified bismuth ferrite (i.e., Bi_1−xDy_xFeO₃; x=0–0.2 with the interval of 0.05) (BDFO) were synthesized using a high-temperature solid-state reaction method. Preliminary X-ray structural analysis showed that the reported crystal structure of BiFeO₃ (rhombohedral) is invariant even with Dy-substitution at the Bi-site upto x=0.2. The scanning electron micrograph of the compounds showed (i) the uniform distribution of grains on the sample surface with high density and (ii) reduction of grain size on increasing Dy content in BiFeO₃ (BFO). Studies of impedance, electrical modulus and electric conductivity of the materials in wide frequency (10–1000 kHz) and temperature (30–500 °C) ranges using a complex impedance spectroscopy technique have provided new and interesting information on the contribution of grains, grain boundary and interface in these parameters. Detailed studies of impedance spectroscopy clearly exhibit the dielectric relaxation of non-Debye type. The ac conductivity of the Dy-substituted BFO obeyed Jonscher's universal power law. An increase in Dy-content in BDFO results in the increase of spontaneous magnetization of BFO due to the collapse of spin cycloid structure.     

Structural,electrical, magnetic and magnetoelectric properties of Co-doped BaTiO3 multiferroic ceramics

In this work, BaTi_1-xCo_xO₃ (BTCO) ceramics with x?=?0, 2.5, 5, 7.5 and 10?mol% have been synthesized and their structural, electrical, magnetic and magnetoelectric have been investigated. Rietveld refinement of XRD data reveals that pure BTO has pure tetragonal phase. On the other hand, between 2.5?≤?x?≤?7.5, BTCO shows both tetragonal as well as hexagonal phases. At x?=?10?mol%, BTCO shows only hexagonal phase. The grain size of the BTCO samples is found to increase with Co doping concentration. The ferroelectric polarization and relative permittivity of BTCO samples reduce with an increase in the Co concentration. A standard magnetization equation is used for fitting the magnetic hysteresis (M-H) curve, thus deconvoluting the ferromagnetic (FM) and paramagnetic (PM) components. The saturation magnetization (M_s) gradually increases from x?=?2.5 to x?=?10?mol%, the value being 0.8 memu/g and 8.92 memu/g respectively. The origin of magnetization is due to the oxygen vacancies and their associated exchange interaction. The magnetodielectric coefficient (MD) shows a reducing trend from 1.80 to 0.18 for x?=?2.5 to x?=?10?mol% respectively. The magnetoelectric coefficient $({\alpha }_{\mathit{ME}})$ for x?=?2.5?mol% is 3.399?mV/cm. Oe, while for x?=?10?mol% it is 0.896?mV/cm. Oe.     

Optical and ferromagnetic properties of hydrothermally synthesized CeO2/CuO nanocomposites

Nanostructured CeO₂/CuO composites are synthesized using a facile hydrothermal reaction. Results signify that Cu ions prefer to enter into CeO₂ lattice forming solid solution at low concentration, and would be transformed into CuO phase at moderate concentration. Moreover, the addition of CuO species into CeO₂ promotes the reduction of Ce⁴⁺ and the creation of oxygen vacancy (V_O) defects. Raman analyses confirm V_O concentration initially increases and then decreases with the increasing CuO phase and the sample Ce1Cu2 exhibits the highest defect concentration. The room temperature ferromagnetic behavior is observed firstly in CeO₂/CuO nonmagnetic system and the maximal saturation magnetization appears in Ce1Cu2. The emergent ferromagnetism appears to be relevant to the extensive V_O defects, which can be interpreted by the indirect double-exchange model. The synthetic interaction between CeO₂ and CuO results in the redshift of the bandgap in prepared CeO₂/CuO nanocomposites.     

Dispersion studies of La substitution on dielectric and ferroelectric properties of multiferroic BiFeO3 ceramic

Lanthanum La-substituted multiferroic Bi_1−xLa_xFeO₃ ceramics with x = 0.0, 0.05, 0.10, 0.15, 0.20 and 0.25 have been prepared by solution combustion method. The effect of La substitution for the dispersion studies on dielectric and ferroelectric properties of Bi_1−xLa_xFeO₃ samples have been studied by performing x-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), density, dc resistivity and dielectric measurements as well as characterizing the polarization-field hysteresis loop. The results of prepared samples are compared with those of bismuth ferrite (BiFeO₃). In the measuring frequency of 10 KHz to 1 MHz, the dielectric constants and dielectric losses for samples x = 0.20, 0.25 are almost stable and exhibited lowest dielectric loss close to 0.1. The resistivity of Bi_1−xLa_xFeO₃ samples reaches a maximum value of 10⁹ ohm-cm, which is about three times higher than that for pure BiFeO₃. The results also show that stabilization of crystal structure and nonuniformity in spin cycloid structure by La substitution enhances the resistivity, dielectric and ferroelectric properties. Furthermore, the substitution of rare earth La for Bi helps to eliminate the impurity phase in BiFeO₃ ceramic.     

Effects of Nd3+ and high-valence Nb5+ co-doping on the structural,dielectric and magnetic properties of BiFeO3 multiferroics

Bi_0.90Nd_0.10Fe_1?xNb_xO₃ (0 ≤ x ≤ 0.05) multiferroics have been studied to reveal the effect of Nb doping on the physical properties of the neodymium modified BiFeO₃. These samples have been synthesized via conventional solid state reaction method. The structural characterization was performed by XRD technique and Rietveld refinement. Rietveld refinement results confirmed that all samples crystallized in rhombohedral symmetry. In the vicinity of anti-ferromagnetic Neel-temperature (T_N), an anomaly was observed in dielectric constant (?′) and loss tangent (tan δ) which indicates the existence of magnetoelectric coupling. It is observed that with Nb doping dielectric constant was reduced and Neel temperature shifted towards higher temperature. The impedance (Nyquist plots) and modulus spectroscopy revealed that materials possess non-Debye type of relaxation. The doping of donor ion is able to suppress the existence of oxygen vacancies which results in increase in resistivity. The B-site doping by higher valence ion suppresses the existing modulated spin structure by structural distortion, results in released net magnetization. The room temperature remanent magnetization increased with Nb doping and all powder samples possess weak ferromagnetism. The possible reasons for the notable magnetic and dielectric performance of prepared samples were discussed.     

Room temperature ferromagnetic behavior,linear and nonlinear optical properties of KNbO3 microrods

Microrods of potassium niobate (KNbO₃) were synthesized at 700, 800 and 900 °C by solid state reaction method and their structural, morphological, linear optical, nonlinear optical and magnetic properties were studied. X-ray diffraction and Rietveld refinement reveal that all the prepared KNbO₃ samples belong to single phase orthorhombic structure with space group of Cm2m. Fourier transform infrared and Raman spectral analyses confirmed the Nb-O symmetric stretching vibrational modes of NbO₆ octahedron. The grain growth direction (001) and inter planar spacing (0.38 nm) of KNbO₃ were determined by high resolution transmission electron microscopy. Field emission scanning electron microscopy images revealed that KNbO₃ are formed with nearly rod shape morphology with average diameter varying from 471 to 678 nm and length lies between 1.2 and 2.3 µm. X-ray photoelectron spectroscopy and energy dispersive X-ray spectroscopy studies confirmed the presence of K, Nb and O elements in the KNbO₃ matrix. UV–visible diffuse reflectance spectra showed that the band gap of KNbO₃ microrods varies between 3.18 and 3.22 eV. The existence of blue (492 nm) and green (521 nm) emissions evidently showed the presence of oxygen vacancy in the samples. All the synthesized KNbO₃ microrods exhibited relatively high SHG efficiency as compared with that of the standard KDP. Vibrating sample magnetometer analysis showed the existence of ferromagnetic behavior at room temperature. The saturation magnetization (M_s) of KNbO₃ microrods lies between 0.015 and 0.012 emu g^?1 and coercive field (H_c) varies in the range from 489 to 420 Oe.     

Lower power dependent upconversion multicolor tunable properties in TiO2:Yb3+/Er3+/ (Tm3+)

Multicolor tunable upconversion luminescence materials could be applied to polychromatic LED and anti-counterfeit due to their superiority in abundant color and security feature. However, the harsh terms to achieve emission tuning associated with the drawbacks, including changing the concentration or types of doping ions, higher temperature, and higher excitation power, limit the range of its application. In this paper, a convenient and versatile approach for multicolor-emitting is realized via simply lower power modulating in TiO₂:Yb³⁺/ Er³⁺ and TiO₂: Yb³⁺/Er³⁺/Tm³⁺. The emission color is tuned from pink to yellowish green in TiO₂:Yb³⁺/ Er³⁺ and tuned from white to yellowish green in TiO₂: Yb³⁺/Er³⁺/Tm³⁺. It's found that there is no apparent temperature variation at lower power. Meanwhile, the mechanism of the emission and the multicolor tunability is discussed.     

Effect of electric poling on structural,magnetic and ferroelectric properties of 0.8PbFe0.5Nb0.5O3-0.2BiFeO3 multiferroic solid solution

The effect of electric poling on structure, magnetic and ferroelectric properties of 0.8PbFe_0.5Nb_0.5O₃-0.2BiFeO₃ (0.8PFN-0.2BFO) multiferroic was studied through XRD, Raman, magnetic and ferroelectric measurements. Single step solid state reaction method was adopted to synthesize single phase 0.8PFN-0.2BFO multiferroic at lower calcination and sintering temperature. Room temperature (RT) XRD pattern before and after poling confirmed the monoclinic structure with Cm space group. Rietveld refined XRD for poled and unpoled sample shows the influence of electric poling on Fe-O1, Fe-O2, Nb-O and Bi-O modes. There is a small variation in the lattice parameters after electric poling. The structural properties were also studied in detail for the poled and unpoled 0.8PFN-0.2BFO using Raman spectroscopy. Raman measurements were carried out over a wide range of temperature (250–550 K) for both poled and unpoled samples. At RT unpoled 0.8PFN-0.2BFO multiferroic exhibit 8 active modes at 211, 263, 440, 484, 571, 706, 785 and 1120 cm^-1 in the frequency range 100–1200 cm^-1. The Raman peaks exhibits significant changes in intensity as well as shape of the spectra at the characteristic temperature T_C (470 K) and T_N (310 K). Poled Raman spectra show major changes in the Fe/Nb-O modes intensities around T_N and are due to dynamic nature of spin phonon coupling. Changes observed in the temperature dependent magnetic measurements i.e. ZFC/FC and M − H loop evidence the existence of converse magneto-electric coupling (CME) and this is due to the poling effects on Fe-O, Nb-O active modes. Due to rotation of the oxygen octahedral the electric field induced strain will originate in the system. P-E loops after poling show an increase in remnant polarisation and coercive field due to an improvement in domain ordering. The potential tunability of magnetisation with electric poling is an ideal tool for realisation of application in practical devices.     

Effect of non-magnetic Al3+ doping on structural,optical, electrical,dielectric and magnetic properties of BiFeO3 ceramics

Pure BiFeO₃ (BFO) and Al doped BFO samples were synthesized via citrate precursor method and sintered at 500 °C for two hours. Effect of Al doping on the structural, optical, electrical, dielectric and magnetic properties were investigated. X-ray diffraction (XRD) confirmed the distorted rhombohedral structure without any merging of peaks which indicates no structural transformation. Average crystallite size was found to be in the range 28–39 nm. Field emission scanning electron microscopy (FESEM) images illustrated the dense, agglomerated, spherically shaped with reduced grain size nanoparticles. Increased value of dielectric constant with low dielectric tangent loss was observed for the Al doped BFO samples. The value of dielectric constant was found to be 51 at 100 kHz for x = 0.1 sample. Temperature dependent dielectric constant showed a dielectric anomaly, indicating the antiferromagnetic transition. The remanent polarization and the corresponding coercive field for x = 0.1 was found to be 0.0625 µC/cm² and 56.154 kV/cm at an operating voltage of 1000 V. The improved electrical properties with low leakage current density were ascribed to the stabilization of the pervoskite structure and reduced oxygen vacancies.     

Improving sintering behavior of MWCNT/BaTiO3 ceramic nanocomposite with Bi2O3-B2O3 addition

The present research systematically investigated the novel low-temperature fabrication of a multi-walled carbon nanotube (MWCNT)/barium titanate nanocomposite using a two-step mixing technique. The synthesis was conducted using different amounts of MWCNT (0.25%, 0.5%, 1%, 2%, 4%, and 8% wt) with different compositions of (Bi₂O₃ + B₂O₃) as a sintering aid. Scanning and transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, three-point bending strength, Vickers hardness indentation and Archimedean technique were used to characterize the as-synthesized specimens. It was found that the appropriate content of sintering aid (Bi₂O₃+B₂O₃) strongly decreased the sintering temperature from 1200 °C to 950 °C. The results also revealed that any sintering aid with the optimum composition that included 30% (mol) Bi₂O₃ was optimal for a sintering aid content of 6% (wt). Consequently, the highest values of the flexural strength and fracture toughness were achieved by applying the optimal amounts of MWCNT (1% wt) and sintering aid (6% wt).     

Structural,magnetic, vibrational and impedance properties of Pr and Ti codoped BiFeO3 multiferroic ceramics

Single-phase (Bi_1−xPr_x)(Fe_1−xTi_x)O₃ ceramics (x=0.03, 0.06, and 0.10 as BPFT-3, BPFT-6 and BPFT-10, respectively) were synthesized by conventional solid state reaction method. The effect of varying Pr and Ti codoping concentration on the structural, magnetic, dielectric and optical properties of the BPFT ceramics have been investigated. X-ray diffraction indicated pure rhombohedral phase formation for BPFT-3 and BPFT-6 ceramics, however, a structural phase transition from a rhombohedral to an orthorhombic phase has been observed for BPFT-10 ceramic. The maximum remnant magnetization of 0.1824 emu/g has been observed in BPFT-6. With increasing codoping concentration the room temperature dielectric measurements showed enhancement in dielectric properties with reduced dielectric loss. UV–vis diffuse reflectance spectra demonstrated the strong absorption of light in the visible region for a band gap variation 2.31–2.34 eV. Infrared spectroscopy indicated the shifting of Bi/Pr–O and Fe/Ti–O bonds vibrations and change in Fe/Ti–O bond lengths. Decrease in the conductivity on increasing Pr and Ti concentration in BFO is attributed to an enhancement in the barrier properties leading to suppression of lattice conduction path arising due to lattice distortion as confirmed from impedance analysis.     

Structural and ferroelectric properties of hafnium substituted BiFeO3 multiferroics synthesized via auto combustion technique

A series of BiFe_1-xHf_(3/4)xO₃ ( 0%, 5%, 10%, 15% and 20%) nanoparticles were synthesized by simple auto combustion technique using citric acid as a fuel. Thermogravimetric (TGA), differential thermogravimetric (DTA), structural, magnetic, dielectric and ferroelectric analyses were investigated. Thermogravimetric analysis provides information of temperature at which phase develops (600?°C). DTA predicts ferroelectric to paraelectric transformation temperature which is found to be 822?°C. X-ray diffraction (XRD) results confirm formation of distorted rhombohedral structure for all compositions along with few traces of Bi₂₅FeO₄₀. The tolerance factor is increased from 0.845 to 0.853 due to larger ionic radius of Hf⁴⁺ substitution on Fe site. Crystallite size (D) is found in the range of 24.2–30.48?nm. Saturation magnetization (Ms) is increased to 16 times and remanent magnetization (Mr) is increased to 8 times than that of pure BiFeO₃. This increment in magnetic parameters is due to reduction of oxygen vacancies, small crystalline size (less than 62?nm), structural distortion and unbalancing condition for antiferromagnetic magnetic moments of Fe³⁺ ions. Dielectric parameters depict decrement behavior with increasing of applied field up to 3?GHz. For Fe_1-xHf_(3/4)xO₃, lower value of dielectric permittivity for all compositions is due to reduction of polarization and less growth of grains but more growth of grain boundaries because of mismatching of Hf and Fe³⁺ ions. P-E hysteresis loop changes from round shape to elliptical shape and it confirms less lossy nature of ferroelectric loops. Higher values of Ms as well as Mr but lower values of dielectric constant as well as remanent polarization for these nanoparticles make them useful for MeRAM (magnetoelectric random access memory) and high resonant applications.     

Photocatalytic,magnetic, and electrochemical properties of La doped BiFeO3 nanoparticles

We successfully prepared La_1?xBi_xFeO₃ (L_xB_1?xFO, x?=?0.01–0.1) nanoparticles using a sol-gel technique, and studied their photocatalytic, magnetic, and electrochemical properties. Structural refinement studies of the prepared nanoparticles revealed a gradual structural transition from rhombohedral to orthorhombic. The average grain size was observed to decrease with increasing the concentration of La. The photocatalytic degradation of Rhodamine B (RhB) in the presence of the prepared nanoparticles was studied under visible light irradiation. The L_0.06B_0.94FO nanoparticles showed higher degradation efficiency compared to pure BiFeO₃ (BFO) nanoparticles. Magnetic studies showed that La doping improved the magnetization of BFO due to the reduction in grain size and destruction of cycloid coupling of spins. Higher specific capacitance values were obtained for La doped BFO (LBFO) nanoparticles compared to BFO nanoparticles. A maximum specific capacitance of 219?F?g^?1 was obtained at a current density of 1?A?g^?1 for LBFO nanoparticles.     

MgTiO3/TiO2/MgTiO3: An ultrahigh-Q and temperature-stable microwave dielectric ceramic through cofired trilayer architecture

A cofired trilayer ceramic architecture showing as MgTiO₃/TiO₂/MgTiO₃ was designed to realize temperature-stable and ultrahigh-Q microwave dielectrics in the typical MgTiO₃-TiO₂ system. The effects of TiO₂ content on the microwave dielectric properties of cofired trilayer ceramics were studied. Through the design of cofired trilayer architecture, the chemical reactions between MgTiO₃ and TiO₂ were limited within a narrow region of MgTiO₃/TiO₂ interfaces (~ 15?µm in width), which could be beneficial for optimizing the microwave dielectric properties. Excellent characteristics of ε_r ~ 18.38, Q×f value ~ 169,900?GHz and τ_f ~ ??1?ppm/°C were gained for the MgTiO₃/TiO₂/MgTiO₃ ceramic architectures stacked with 1.63?vol% TiO₂. The current work could serve as new strategies to develop high-performance dielectric resonators and multilayers for 5G wireless communication applications.     

Tuning magnetic properties of BiFeO3 thin films by controlling Mn doping concentration

Mn-doped BiFeO₃ (BiFe_1–xMn_xO₃, x = 0, 0.03, 0.05, 0.10, 0.15 and 0.20) polycrystalline multiferroic thin films were successfully synthesized using the facile sol-gel spin-coating method. The crystal structures, surface features, elements valences, and magnetic properties of as-prepared samples were systematically explored. X-ray diffraction and Raman spectroscopy studies revealed the substitutions of Mn into the Fe site and a rhombohedral-to-orthorhombic phase transition. The Field Emission Scanning Electron Microscopy showed a decrease in the average particle sizes and an improvement of surface morphology with increasing the concentration of the substitutes. Energy-dispersive X-ray spectroscopy confirmed the doping concentration of Mn²⁺ in the samples. X-ray photoelectron spectroscopy indicated the co-existence of Mn²⁺/Mn³⁺ ions in the doped films. The remnant magnetization value of BiFe_0.90Mn_0.10O₃ thin film was found to be approximately six times than that of pure BiFeO₃ thin film under a magnetic field of 10 kOe. The enhanced magnetic property of BiFe_0.90Mn_0.10O₃ thin film was mainly ascribed to the structural distortion of spin cycloid and the enhancement of super-exchange interaction between the Fe³⁺ (Mn²⁺) and O^2- ions.     

Structural,vibrational, optical,magnetic and dielectric properties of Bi1−xBaxFeO3 nanoparticles

Bi_1−xBa_xFeO₃ (x=0.05, 0.10 and 0.15) nanoparticles were synthesized by the sol–gel method. X-ray diffraction and Raman spectroscopy results showed the presence of distorted rhombohedral structure of Bi_1−xBa_xFeO₃ nanoparticles. Rietveld refinement and Williamson–Hall plot of the x-ray diffraction patterns showed the increase in lattice parameters, unit cell volume and the particle size. Infrared spectroscopy and Raman analysis revealed the shifting of phonon modes towards the higher wavenumber side with increasing Ba concentration. These samples exhibited the optical band gap in the visible region (2.47–2.02 eV) indicating their ability to absorb visible light. Magnetic measurement showed room temperature ferromagnetic behavior, which may be attributed to the antiferromagnetic core and the ferromagnetic surface of the nanoparticles, together with the structural distortion caused by Ba substitution. The magnetoelectric coupling was evidenced by the observation of the dielectric anomaly in the dielectric constant and the dielectric loss near antiferromagnetic Neel temperature in all the samples.     

Improvement of Al3+ ion conductivity by F doping of (Al0.2Zr0.8)4/3.8NbP3O12 solid electrolyte for mixed potential NH3 sensors

New Al³⁺ ion conducting solid electrolytes (Al_0.2Zr_0.8)_4/3.8NbP₃O_12-xF_2x(0?≤x?≤?0.4) with Nasicon-structure are successfully prepared by solid state reaction method. The influences of the doped F^- content on the properties of the (Al_0.2Zr_0.8)_4/3.8NbP₃O_12-xF_2x samples are investigated using X-ray powder diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The results show that F^- doping can effectively improve the sinterability and the total conductivity of the (Al_0.2Zr_0.8)_4/3.8NbP₃O_12-xF_2x samples. Among the solids series, (Al_0.2Zr_0.8)_4/3.8NbP₃O_11.7F_0.6 shows the highest conductivity of 1.53?×?10^?3 S?cm^?1at 500?°C, which is approximately 7.9 times higher than that of the undoped (Al_0.2Zr_0.8)_4/3.8NbP₃O₁₂. The ion transference number of the samples is higher than 0.99 at 300–700?°C. On the basis of the promising properties, a mixed-potential type NH₃ sensor based on (Al_0.2Zr_0.8)_4/3.8NbP₃O_11.7F_0.6 electrolyte and In₂O₃ sensing electrode has been developed. The sensing performance of the sensor is evaluated. The mixed-potential type sensor can work at relatively low temperatures of 200–350?°C and an excellent sensitivity of 99.71?mV/decade at 250?°C is obtained. The sensor also displays excellent stability and reproducibility, accompanied by low cross-sensitivities to CO₂, CH₄ and H_2.     

Dielectric properties of Bi-doped Ba0.8Sr0.2TiO3 ceramic solid solutions

Bismuth-doped barium–strontium–titanate ceramics of the formula (Ba_0.8Sr_0.2)_(1−1.5y)Bi_yTiO₃ were prepared using a conventional solid-state reaction method. The structure, dielectric properties, and ferroelectric relaxor behaviour of all compositions were thoroughly investigated. The findings revealed a broad dielectric anomaly and a shift in dielectric maxima towards higher temperatures with increasing frequency. The diffuseness degree indicator γ was about 1.68, and dielectric relaxation was noted to follow the Vogel–Fulcher relationship, with T_f=185 K, f₀=1.18×10¹⁰ Hz, and Ea=0.35 eV, which further supported the spin-glass-like properties of BBSTs. The latter were also noted to display significant ferroelectric relaxor behaviour that could be attributed to the presence of Bi³⁺ doping ions. The degree of relaxation behaviour was noted to increase with the increase in bismuth concentration. Raman spectra were investigated as a function of temperature, and the findings confirmed the results from X-ray and dielectric measurements. Among the compositions assayed in this solid solution, 10% Bi-doped Ba_0.8Sr_0.2TiO₃ yielded promising relaxor properties that make it a strong candidate for future industrial application in the production of efficient and eco-friendly relaxor ferroelectric materials.     

Synthesis and multiferroism in mechanically processed BiFeO3–PbTiO3 ceramics

In this study, (1 − x)BiFeO₃–(x)PbTiO₃ multiferroic ceramics, with x = 0, 0.1, 0.2, 0.25, 0.3 and 0.4, were processed through high-energy ball milling followed by reactive sintering in air atmosphere. The optimization of the procedure for the preparation of highly-dense (1 − x)BiFeO₃–(x)PbTiO₃ ceramics was carefully investigated and structural/microstructural effects on ferroic properties were carefully addressed. Shrinkage dilatometric measurements revealed an expansion related to a sintering reaction that has occurred before densification. This sintering behaviour was highly PbTiO₃ concentration-dependent. The sintering mechanism was found to be directly related with the aliovalent substitution of Pb and Ti ions on A and B sites of the perovskite structure. The obtained ceramics were confirmed as ferroelectric ordered in ferroelectric characterizations. Remnant polarizations and coercive fields greatly dependent on grain size distribution and aliovalent substitutions were revealed. The magnetic hysteresis displayed a weak-ferromagnetic behaviour in all studied samples.     

Thermoelectric properties of Bi2O3-added WO3 ceramics

Tungsten trioxide (WO₃) ceramics were prepared by firing Bi₂O₃-added WO₃ compacts with atomic ratios of Bi/W?=?0.00, 0.01, 0.03, or 0.05, in which Bi₂O₃ was mixed as a sintering agent. Dense ceramics consisting of remarkably grown WO₃ grains were obtained for Bi-containing samples with Bi/W?=?0.01, 0.03, and 0.05. The grain growth was enhanced by the liquid phase of Bi₂W₂O₉ formed among the WO₃ grains while firing. The XRD patterns did not show evidence for Bi inclusion into the WO₃ lattice, but the SEM-EDX showed an intensive distribution of Bi into the grain boundaries. Electrical conductivity σ and Seebeck coefficient S were measured in a temperature range of 373–1073?K. The temperature dependences indicated that the Bi₂O₃-added WO₃ ceramics were n-type semiconductors. It was considered that the electron carriers were generated from oxygen vacancies included into the WO₃ grains. The thermoelectric power factors S²σ for the ceramics ranged from 1.5?×?10^?7 W?m^?1 K^?2 to 2.8?×?10^?5 W?m^?1 K^?2, and the highest value occurred at 970?K for the ceramic with Bi/W?=?0.01.