BiNbO4 Ceramics Research Articles

Energy storage and dielectric properties of PLZST-based antiferroelectric ceramics doped with BiNbO4

In this work, (1-x)(Pb0.97La0.02)(Zr0.5Sn0.44Ti0.06)O3-x BiNbO4 (x = 0–0.15) ceramics ((1-x)PLZST-xBiNbO4) were prepared by solid state reaction method. By changing the content of BiNbO4, the phase evolution, dielectric properties and energy storage properties were studied comprehensively. It is found that with the increase of BiNbO4 content, there are two peaks of dielectric constant. The mild BiNbO4 doping first destroyed the relaxation behavior of PLZST. Then with the increase in BiNbO4, the local defect dipole forms another weak coupling and reduce the antiferroelectric-ferroelectric phase transition field (EAFE-FE). When x = 0.05, the maximum energy density is 0.82 J/cm3, and the energy efficiency is 88%.

Modelling of Dielectric Properties of BiNbO4-Based Microwave Ceramics

In the present paper results of the studies devoted to computer simulations of dielectric response of electroceramics in a frequency domain as well as analysis of the experimental data are given. As an object of investigations BiNbO4-based microwave ceramics was taken. Simulations of the hypothetical impedance response of the ceramic system were performed under assumption of the brick-layer model. A strategy for analysis and modelling of the impedance data for microwave electroceramics was discussed. On the base of the discussed strategy modelling of the dielectric response of BiNbO4 ceramics was performed with the electric equivalent circuit method. The Voigt’s and Maxwell’s circuits were taken as electric models. Parameters of the electric components of the circuits were determined and related to parameters of the ceramic object under study. It was found that fitting quality was good and changed within the range χ2 = 6.78 × 10–4 – 6.77 × 10–5 depending on the model.

Study of CuO and V2O5 Effect on IR Spectra of Polycrystalline Bismuth Niobate

Bismuth niobate (BiNbO4) ceramics were fabricated by mixed oxide method and sintered by presureless sintering method. BiNbO4 ceramics doped with V2O5 additive in amount 0.125 wt%, 0.250 wt% and 1 wt% of was sintered at T = 910°C whereas BiNbO4 ceramics doped with 2 wt% of CuO additive was sintered at T = 890°C and T = 910°C. It was found that V2O5 additive improved morphology of the ceramic samples. However, the chemical composition of BiNbO4 ceramics in relation to bismuth oxide and niobium oxide manifested a tendency of lack of Bi2O3 component. Absorption bands for the BiNbO4 compound were identified. FTIR band positions associated with NbO6 octahedra suggested that the crystal structure changes after V2O5 incorporation.

The effect of СuO on the microstructure, spectral characteristics, thermal and electrical properties of BiNbO4 ceramics

Thermal and electrical properties of copper oxide doped BiNbO4 ceramics as well as its spectral characteristics and microstructure were studied in this work. According to XRD, the samples calcined at 950 °C and 1100 °C had the structure of α-BiNbO4 in spite of the phase transition α→γ(β) at 1040 °C. The studied composite samples had the composition of BiNb1-хCuх-yO4-δ·yСuO (х≤0.04) and were characterized by the graphite color and visually pronounced grain microstructure. The DSC-curves of the samples revealed the reversible endo-effect near 900 °C associated with copper (II) oxide decomposition and the thermal effects caused by the chain of reconstructive phase transitions α→γ→β’→β in BiNb1-хCuх-yO4-δ. It was established that the presence of copper oxide additive in the samples increased the density of the ceramics, on average, by 8–10% and had a thermostatic effect on the compacted samples manifested in the increase in the α→γ(β) phase transformation temperature by ∼ 100 °C. The mass spectrum of vapor over the BiNb1-хCuх-yO4-δ·yСuO samples in vacuum has shown the ionic currents of Bi+ and O2+. The absence of Cu+ ions in the mass spectrum of vapor was due to low partial pressure of copper vapor. The comparison of the Cu2p-NEXAFS spectra of copper oxides (I) and (II) and BiNb1-хCuх-yO4-δ·yСuO, synthesized at 950 °C and 1100 °C allowed to conclude that copper atoms were in the Cu(II) state in the studied ceramics. The impedance spectroscopy showed that an increase in the copper content reduced the conductivity of the samples synthesized at 950 °C and increased the conductivity of the samples synthesized at 1100 °C. A threefold increase in the copper content led to an increase in low-frequency dielectric losses by 20% in the samples synthesized at 1100 °C. The growth of the capacity of the samples with decreasing frequency indicated the ion-migration nature of polarization.

Low-temperature sintered Bi1-xSmxNbO4 microwave dielectrics

The Bi1-xSmxNbO4 ceramics (x = 0 ∼ 0.1) was prepared by a conventional solid-state reaction at a low temperature from 900℃ to 960℃. The crystal structures of the Bi1-xSmxNbO4 ceramics were single orthorhombic (α-BiNbO4) phase at all sintering conditions. Dielectric constant (εr), Quality factor (Q·f), and the Temperature coefficient of resonant frequency (τf) were significantly affected by Sm3+ substitution. The εr ranged from 42.79 ± 0.5 to 41.71 ± 0.5, with the highest Q·f value of 32,100 ± 1605 GHz in the Bi1-0.99Sm0.01NbO4 ceramic. The Q·f values of the Bi1-xSmxNbO4 ceramics were improved compared to the BiNbO4 ceramics. The τf of the Bi1-xSmxNbO4 ranged from -2.3 ± 0.5 ppm/℃ to -11.4 ± 0.5 ppm/℃. The Clausius-Mossotti equation and additivity rule of dielectric polarizabilities were introduced in order to explain dependence of the dielectric constant as a function of Sm content. The τf of the Bi1-xSmxNbO4 ceramics with Sm content also was associated with the bond valence of the Bi1-xSmxNbO4 ceramics.

Phase transformations and thermal stability of Ni-doped BiNbO4 ceramics

Phase transformations and thermal stability of nickel-containing solid solutions of bismuth orthoniobate BiNbO4 were studied by methods of thermal and X-ray phase analysis. The DSC curve of the BiNb1-xNixO4-δ samples exhibited endothermic effects near the temperatures of 1049 °C and 1227 °C during the heating, and exothermic effects at ˜990 °C during the cooling, which were associated with the phase transition from the orthorhombic to triclinic modification and with congruent melting. In the compacted polycrystalline samples of the solid solutions, the phase transition from the high-temperature triclinic modification to the orthorhombic modification was revealed after calcination at 750 °C for 150 h, as well as after 1 h calcination at 950 °C.

Influence of Dopants on Structure of Polycrystalline Bismuth Niobate

Abstract Bismuth niobate (BiNbO4) has attracted attention as a low-fired ceramics with promising microwave application potential. BiNbO4 ceramics was fabricated by mixed oxide method and sintered at temperature T<1000°C. As the sintering aids a small amount of CuO oxide was used. The crystalline structure of the ceramic samples was examined by X-ray diffraction method at room temperature. The Rietveld refinement method was used for analysis of diffraction data. As a result an influence of dopants on crystal structure of bismuth niobate (BiNbO4) ceramics was revealed. It was found that fabricated BiNbO4 ceramics adopted the orthorhombic symmetry (α-BiNbO4 phase, Pnna (52) space group). Small differences in elementary cell parameters were found.

Mn doped BiNbO4 ceramics: Thermal stability, phase transitions, magnetic properties, NEXAFS and ESR spectroscopy

Thermal stability, magnetic properties, ESR (Electron Spin Resonance) and NEXAFS (Near-Edge X-ray Absorption Fine Structure) spectra of the orthorhombic and triclinic modifications of solid solutions BiNb1-xMnxO4-δ have been studied. X-ray diffraction determined the reversibility of the phase transition from the high-temperature triclinic modification to the orthorhombic modification at 950 °C in the BiNb1-xMnxO4-δ solid solutions. The ESR spectra of the triclinic BiNb1-xMnxO4-δ revealed the sextet structure of Mn(II) ions with 8.4 mT splitting and some features at g = 3.80 and 1.47, and a broad diffuse band with g ∼ 2.2 having a sextet with 8–9 mT splitting and g = 2.0 against its background. The measurements of magnetic susceptibility allowed us to calculate the parameters of exchange interactions in dimers and the distribution of manganese atoms (II), (III) and (IV) in dependence on concentrations of the solid solutions in the orthorhombic and triclinic modifications. It was established that in the manganese-doped solid solutions of triclinic modification, the degree of aggregation and the nuclearity of the clusters were higher than in the solid solutions of orthorhombic modification. The clusters were presented in the forms of dimers and trimers of Mn(II), Mn(III) and Mn(IV) atoms with different valence atoms with antiferro- and ferromagnetic types of exchange.The solid solutions BiNb1-xMnxO4-δ as well as manganese oxides MnO, Mn2O3 and MnO2 were studied by the NEXAFS spectroscopy in order to determine the degrees of oxidation of manganese atoms. The DSC (Differential Scanning Calorimetry) curves of the samples BiNb1-xMnxO4-δ revealed the endothermic effects associated with the phase transition from the orthorhombic modification to the triclinic one at 1050 °C (x = 0.03) and 1048 °C (x = 0.06). The melting peaks were observed at 1231 °C (x = 0.03) and 1220 °C (x = 0.06), respectively. The differences in the magnetic characteristics and in the results of ESR and NEXAFs spectroscopy of the BiNb1-xMnxO4-δ of orthorhombic and triclinic modifications were due to the relative content of Mn(II), Mn(III), Mn(IV) ions and the degree of distortion of their local surroundings, composition and nature of exchange interactions in the clusters of manganese atoms.

Influence of processing conditions on crystal structure of BiNbO4 ceramics

Bismuth niobate (BiNbO4) has attracted attention as a low-fired ceramics with promising microwave application potential. It belongs to the bismutocolumbite oxides with similarly to scheelite-like stibiotantalite structure (SbTaO4) A3+B5+O4. The aim of the present research was to fabricate BiNbO4 ceramics by solid state reaction route from the mixture of simple oxides viz. Bi2O3, and Nb2O5, and study its phase composition as well as crystal structure by X-ray diffraction method. The Rietveld refinement method was utilized for analysis of diffraction patterns. It was found that the mass change effects finished at temperature T=500°C and the total mass change was about Δm=-0.78%. It was found that BiNbO4 ceramics sintered in ambient air exhibited multiphase composition, i.e., apart from the major α-BiNbO4 phase, the orthorhombic Bi5Nb3O15, Bi3Nb17O47 and cubic Bi3NbO7 phases were present. An increase in sintering temperature caused an increase in the amount of major α-BiNbO4 phase which adopted an orthorhombic symmetry described well by Pnna(52) space group.

柠檬酸法制备BiNbO<sub>4</sub>陶瓷及其相变和介电性能研究

以自制的水溶性过氧化柠檬酸铌为原料，利用柠檬酸法制备BiNbO4介电材料。纯的β相BiNbO4粉体可以在700℃和1050℃获得并在低温β相的BiNbO4粉体中观测到奇异相变：低温β相转变为α相。与同等退火条件的粉体相比，陶瓷样品的结构中存在Bi5Nb3O15晶相残余，这导致陶瓷样品中有气孔出现并有局部的晶粒异常长大。1000℃和1050℃烧结获得的BiNbO4陶瓷比较致密，介电性质随频率和温度变化较小；在1 MHz，1000℃和1050℃烧结BiNbO4陶瓷的介电常数和介电损耗分别为44，0.026和35，0.018。 BiNbO4 have been successfully prepared by a citrate method using home-made water-soluble Nb-citrate-peroxide. Pure β-BiNbO4 powders are obtained at 700˚C and 1050˚C respectively, and observed the abnormal phase transition from low temperature β to α phase. Compared to BiNbO4 powders, the ceramic samples have residual Bi5Nb3O15 phase under the same calcination condition, which results in the existence of pores and locally abnormal grain growth in ceramics. The ceramics calcined at 1000˚C and 1050˚C have denser structures and smaller change of dielectric performance versus frequency and temperature. The dielectric permittivity and dielectric loss of BiNbO4 ceramics calcined at 1000˚C and 1050˚C are 44, 0.026 and 35, 0.018 at 1 MHz respectively.

The stability and dielectric performance of BiNbO4 prepared by citrate method assisting sintering process

Low‐temperature β phase BiNbO4 powders (denoted as Low‐β) were prepared by a citrate method using home‐made water‐soluble niobium precursors. The stability of Low‐β was systematically investigated from the aspects including calcination temperature, incubation time, and stress existing in pellets. Pure Low‐β can be obtained between 700 and 750 °C and the crystal evolution of Low‐β has not completed yet, compared with high‐temperature β phase. Low‐β is kinetically stable and no phase transition occurs when increasing the incubation time below 750 °C. Above 750 °C, both the calcination temperature and incubation time can induce the abnormal phase transition from Low‐β to α phase; also, stress existing in pellets can effectively activate the phase transition of Low‐β. We can conclude that the Low‐β is thermodynamically unstable, while in kinetics, Low‐β is stable. The dielectric properties of BiNbO4 ceramics were investigated to analyze the influence of phase of BiNbO4 powders precursors, especially the effect of phase transition of Low‐β. It's found that BiNbO4 powders firstly calcined at 700 °C is the best precursor to prepare dense ceramics with uniform grain size and the dielectric permittivity and dielectric loss of BiNbO4 ceramics prepared at 1000 °C is 56.6 and 0.001 at 10 kHz, respectively.

Structural, morphological and dielectric properties of BiNbO4 ceramics prepared by the sol-gel method

BiNbO4 ceramic powders were prepared using the sol-gel method. The fine particles were pressed into cylinders and, then, they were treated at temperatures between 500 and 1150°C.The structure was studied by X-ray diffraction and Raman spectroscopy and the morphology was observed by scanning electron microscopy.The measurements of the complex permittivity were made in a resonant cavity operating at 2.7GHz, using the small perturbation method.The reversible phase transformation between β-BiNbO4 and α-BiNbO4 was observed.The density, dielectric constant (ε') and the dielectric loss (tg δ) of the prepared powders increase with the sintering temperature, and the sample treated at 1150°C shows the highest ε' and the highest Q×f.

Influence of Bismuth Content on Complex Immittance Characteristics of Pressureless Sintered BiNbO4 Ceramics

Abstract Goal of the present research was to study immittance properties of BiNbO4 ceramics fabricated by the solid state reaction route followed by pressureless sintering. Four sets of samples were examined, namely the one fabricated from the stoichiometric mixture of oxides, viz. Bi2O3 and Nb2O5 as well as the ones with an excess of 3%, 5% and 10% by mole of Bi2O3. The immittance properties were studied by impedance spectroscopy. Measurements were carried out within the frequency range ν =20Hz-1MHz and temperature range T =RT-550°C. The Kramers-Kronig data validation test was employed in the impedance data analysis. It was found that complex impedance first increases with an increase in Bi2O3 content and decreases for 10mol% excess of Bi2O3. Two relaxation phenomena manifested themselves at elevated temperature (T>267°C) within the measuring frequency range. The conductivity relaxation phenomenon (M″(ν) spectra) took place at higher frequency than the phenomenon with dominant resistive component (Z″(ν) spectra).

Dielectric Properties of BiNbO<sub>4</sub>-Based Ceramic-Polymer Composites with 0-3 Connectivity

In the present study two-phase BiNbO4//PVDF composites with 0-3 connectivity were studied by impedance spectroscopy within the frequency range Δν=100Hz-1MHz at room temperature. Polyvinylidene fluoride (PVDF) acted as a matrix whereas bismuth niobate (BiNbO4) powder acted as a dispersed phase. The volume fraction of the ceramic phase was cV=2, 4, 6, 8, 10, 16 and 20vol%. Analysis of the impedance data registered for composites as well as for BiNbO4 ceramics and PVDF polymer was performed on the base of complex dielectric permittivity mathematical formalism. It was found by impedance spectroscopy that concentration of the dispersed phase had an effect on dielectric properties of ceramic-polymer composite. Experimental data of impedance spectroscopy were fitted to the corresponding equivalent circuit using the complex non-linear least squares method. An equivalent electric circuit consisting of a series combination of two parallel combinations of a resistance R and a constant phase element CPE was found to describe well the dynamic dielectric response of the objects under study. Parameters of the equivalent electric circuit were calculated and it was found that two distinct relaxation processes were present in the composite samples. It was also found that volume fraction of the dispersed phase cV=8vol% corresponded to a local minimum of resistance whereas cV=10vol% of the dispersed phase corresponded to a local minimum of capacitance.

Effect of Bi2O3 Excess on Morphology and Structure of BiNbO4 Ceramics

Abstract Goal of the present research was to fabricate BiNbO4 ceramics from the mixture of powders by the solid state reaction route and pressureless sintering at various temperatures (TS =8700C and TS =9100C) and study microstructure, phase composition and crystalline structure of BiNbO4 ceramics. Four batches were fabricated and examined, namely the one fabricated from the stoichiometric mixture of reagent - grade oxide powders, viz. Bi2O3 and Nb2O5 as well as the ones with an excess of 3%, 5% and 10% by mole of Bi2O3. It was found that apart from the main orthorhombic -BiNbO4 phase additional phases, namely tetragonal Bi5Nb3O15, and cubic Bi3NbO7 are possible to form from the mixture of bismuth oxide and niobium oxide. It was found that -BiNbO4 ceramics exhibited the orthorhombic symmetry identified as Pnna (52). However, small differences in elementary cell parameters were found for the samples sintered from stoichiometric and non-stoichiometric mixture of initial powders.

Effects of V2O5 Additive on Structure and Dielectric Properties of BiNbO4 Ceramics

Abstract Goal of the present research was to investigate the influence of V2O5 additive on the structure and dielectric properties of BiNbO4 ceramics. To fabricate BiNbO4 ceramics with V2O5 added the solid state reaction route and pressureless sintering was utilized. Thus obtained ceramics was characterized in terms of its microstructure (SEM), chemical composition (EDS), phase composition and crystalline structure (X-ray phase and structural analysis, respectively). Also dielectric properties in both temperature and frequency domains were investigated. The impedance spectroscopy was utilized for dielectric characterization and the measurements of complex impedance were performed within the frequency range ν =10Hz-1MHz and temperature range T =RT-550°C. It was found that V2O5 additive changed slightly lattice parameters of BiNbO4 ceramics, decreased porosity of samples and revealled relaxation phenomena within the frequency ranges ν =102-103 Hz and ν =105-106 Hz at temperature T>285°C.

Copper concentration effect in the dielectric properties of BiNbO4 for RF applications

In this paper, the structural and dielectric properties BiNbO4 as a function of cooper addition level and the radio frequency was investigated. The BiNbO4 ceramics, were prepared by using the solid-state reaction method with the addition of 3, 5, and 10wt.% of CuO. The analysis by X-ray diffraction (XRD) using the Rietveld refinement confirmed the formation of single-phase compound with a orthorhombic crystal structure (a=5.6792Å, b=11.7081Å and c=4.9823Å; α=β=γ=90°) for the calcined powders. Micrographs obtained by scanning electron microscope shows the distribution of grains and the behavior of addition of CuO on the sample surface. In the measurements of the dielectric properties of BiNbO4 at room temperature, by complex impedance spectroscopy technique, showed that the largest values of dielectric permittivity (εr′) at frequency 10kHz, were found for the samples: BNO3Cu (3wt.%CuO), BNO5Cu (5wt.% CuO) and BNO10Cu (10wt.% CuO) with values εr′=87.15, 88.63 and 140.73, respectively. The values of the dielectric loss (Tanδ) for the samples: BNO3Cu, BNO5Cu and BNO10Cu were around 10−2, with values of 1.27×10−2, 1.81×10−2, and 3.61×10−2, respectively at 10MHz. The samples were investigated for possible applications in radio frequency devices like ceramic capacitors.

Fabrication and Study of BiNbO<sub>4</sub> Ceramics

Aim of the present research was to fabricate and study crystalline structure as well as dielectric properties of BiNbO4 ceramics. In the present study BiNbO4 ceramics was fabricated by solid state reaction from the mixture of simple oxides viz. Bi2O3, and Nb2O5. Stoichiometric mixture of the powders was thermally analyzed so parameters of the thermal treatment were determined. The EDS measurements proved conservation of the chemical composition of the ceramic powder after calcination (T=800°C). Free sintering at T=870 – 1080 °C was used for fabrication of the ceramic samples. Morphological analysis using scanning electron microscopy was performed. The crystalline structure of the sintered samples were examined by X-ray diffraction method at room temperature. It was found that for low temperature of sintering (T0C) bismuth niobate crystallized in orthorhombic symmetry Pnna (52) whereas for high sintering temperature (T>1000 °C) BiNbO4 exhibited anorthic symmetry P-1 (2). Low frequency (ν=100Hz – 1MHz) impedance spectroscopy was applied to study influence of the sintering temperature on dielectric properties of bismuth niobate at room temperature. The equivalent circuit method was used for analysis of the impedance data.

Application of AC Impedance Spectroscopy for Characterization of BiNbO<sub>4</sub> Ceramics

Impedance spectroscopy is known as an important technique used for describing the electrical processes occurring in a system on applying an ac signal as input perturbation. In the present paper results of a study of BiNbO4 ceramics fabricated by mixed oxide method and sintered by free sintering are reported. Results on the ac response of the electroceramic samples by impedance spectroscopy at temperature T= 100 – 400 °C are given. The usual representation (i.e. Z” vs. Z’ where Z’ and Z” are the real and imaginary parts of the complex impedance, respectively) as well as the alternative representations of the impedance measurement (electrical modulus representation) was used to interpret the impedance spectra of BiNbO4 ceramics in order to obtain separate contributions of the bulk, grain boundary and electrode processes. The Kramers-Kronig data validation test was employed in the impedance data analysis. Experimental data of impedance spectroscopy were fitted to the corresponding equivalent circuit using the complex non-linear least squares method. Agreement between experimental and simulated data was established.

Study of the structural and dielectric properties of Bi2O3 and PbO addition on BiNbO4 ceramic matrix for RF applications

In this paper, the structural and dielectric properties of BNO (BiNbO4) was investigated as a function of the external RF frequency and temperature. The BNO Ceramics, prepared by the conventional mixed oxide method and doped with 3, 5 and 10 wt. % Bi2O3–PbO were sintered at 1,025 °C for 3 h. The X-ray diffraction patterns of the samples sintered, shown the presence of the triclinic phase (β-BNO). In the measurements obtained at room temperature (25 °C) was observed that the largest values of dielectric permittivity (e′ r ) at frequency 100 kHz, were for the samples: BNO5Bi (5 wt. % Bi2O3) and BNO5Pb (5 wt. % PbO) with values e′ r ~ 59.54 and e′ r ~ 78.44, respectively. The smaller values of loss tangent (tan δ) were for the samples: BNO5Bi and BNO3Pb (3 wt. % PbO) with values tan δ ~ 5.71 × 10−4 and tan δ ~ 2.19 × 10−4, respectively at frequency 33.69 MHz. The analysis as a function of temperature of the dielectric properties of the samples, obtained at frequency 100 kHz, showed that the larger value of the relative dielectric permittivity was about e′ r ~ 76.4 at temperature 200 °C for BNO5Pb sample, and the value smaller observed of dielectric loss was for BNO3Bi sample at temperature 80 °C, with about tan δ ~ 5.4 × 10−3. The Temperature Coefficient of Capacitance (TCC) values at 1 MHz frequency, present a change of the signal from BNO (−55.06 ppm/°C) to the sample doped of Bi: BNO3Bi (+86.74 ppm/°C) and to the sample doped of Pb: BNO3Pb (+208.87 ppm/°C). One can conclude that starting from the BNO one can increase the doping level of Bi or Pb and find a concentration where one have TCC = 0 ppm/°C, which is important for temperature stable materials applications like high frequency capacitors. The activation energy (H) obtained in the process is approximately 0.55 eV for BNO sample and increase with the doping level. These samples will be studied seeking the development ceramic capacitors for applications in radio frequency devices.