Complex Perovskite Compounds Research Articles

Studies of structural, dielectric, electrical, and optical properties of a multi-doped novel complex perovskite (Bi1/2Na1/2)(Fe1/3Mn1/3W1/3)O3 ceramic for opto-electronic application

(Bi1/2Na1/2)(Fe1/3Mn1/3W1/3)O3 is a new complex perovskite compound synthesized by a solid-state method. A preliminary structural study using the X-ray diffraction (XRD) pattern shows the monoclinic symmetry of the material. The scanning electron microscope (SEM) micrograph shows the dense microstructure or morphology of rectangular shape grains of different dimensions. The purity and elemental composition of the compound were obtained by energy dispersive X-ray (EDX and EDS) spectrum. The analysis of frequency and temperature-dependent relative dielectric constant (εr) impedance and ac conductivity (σac) predict the presence of Maxwell-Wagner type of dielectric dispersion and thermally activated relaxation mechanism. In-depth analysis of impedance and associated factors reveals that they are substantially dependent on temperature and have a significant link with their microstructures. Similar to semiconductors, the nature of impedance spectra displays a negative temperature coefficient of resistance behavior. The electric polarization hysteresis loop shows the ferroelectric behavior and explores the possible applications. The band gap (Eg) is found to be 2.40 eV using the UV-visible spectrum, appropriate for solar and optoelectronic applications. The value of super-capacitance is 58.96 F/g, applicable for an electrode material supercapacitor application. The behavior of leakage currents has also been investigated and found that conduction has been identified as a space-charge conduction mechanism. We are very interested in designing and manufacturing novel dielectric ceramics because of the rising need for the miniaturization of electronic components and the flexibility of applications. Sensors, actuators, transducers, and capacitors are among the most prevalent applications of such types of materials.

Study of synthesis and characterization of triple ions modified bismuth ferrite for electronic devices: (Bi1/2Li1/2)(Fe1/3Mn1/3W1/3)O3

A high-temperature solid-state reaction technique was used to create a lead-free complex perovskite compound of a chemical composition (Bi1/2Li1/2)(Fe1/3Mn1/3W1/3)O3 (BLFMWO) The X-ray diffraction structural study reveals the monoclinic structure of the compound with cell parameters; a= 12.219Å, b= 6.119 Å, c= 9.513Å with β=109.37°. The detailed examination of the room-temperature scanning electron micrograph reveals a distinct microstructure with large and small grains. Extensive studies of the frequency and temperature dependence of capacitive (dielectric) and resistive (impedance and conductivity) behaviors over a wide temperature (25°-500°C) and frequency (1 kHz-1 MHz) range have revealed the dielectric dispersion, relaxation, and non-Debye type of conduction mechanism of the material. The ac conductivity study provides details regarding the conduction mechanism and semiconducting characteristics of the compound. The band gap energy of 3.62 eV emerges from the UV-visible spectrum, indicating that optoelectronic devices might utilize the material. FTIR spectra in the 500 cm-1- 4000 cm-1 range were used to investigate the bonding nature of the produced BLFMWO material. The specific capacitance of BLFMWO is 69.7524 F/g, having significant rate capabilities with pseudo-capacitive performance for super-capacitor applications. A low value of dielectric loss in high-frequency regions is applicable for application in microwave devices.

Ultrahigh Energy Storage Density and High Efficiency in Lead-Free (Bi0.9Na0.1)(Fe0.8Ti0.2)O3-Modified NaNbO3 Ceramics via Stabilizing the Antiferroelectric Phase and Enhancing Relaxor Behavior.

Dielectric capacitors have attracted growing attention because of their important applications in advanced high power and/or pulsed power electronic devices. Nevertheless, the synergistic enhancement of recoverable energy storage density (Wrec > 10 J/cm3) and efficiency (η > 80%) is still a great challenge for lead-free dielectric bulk ceramics. Herein, by introducing complex perovskite compound (Bi0.9Na0.1)(Fe0.8Ti0.2)O3 with a smaller tolerance factor into an NaNbO3 matrix (NN-BNFT), we have achieved and explored stable relaxor antiferroelectric ceramics with enhanced relaxor behavior. Of particular importance is the composition of 0.88NN-0.12BNFT, which exhibits a large electric breakdown strength Eb of 87.3 kV/mm, an ultrahigh Wrec of 12.7 J/cm3, and a high efficiency η of 82.5%, as well as excellent thermal reliability and an ultrafast discharge speed, resulting from the dense microstructure, the moderate dielectric constant, the reduced grain size, the dielectric loss, and the sample thickness. The outstanding energy storage properties of NN-BNFT display great promise in advanced dielectric capacitors for energy storage applications.

Probable thermoelectric materials for promising candidate of optoelectronics for Ba‐based complex perovskite compounds

Structural parameters, electronic band structure, optical spectra, and thermoelectric properties of trigonal Ba3B(Nb, Ta)2O9(B═Sr, Mg, Ca, Hg, Zn, Fe, Ni, Mn, Co, and Ca) compound materials are investigated. The computations are performed using density-functional calculations within the generalized gradient approximation. The calculated a and c parameters agree with those of the experiment to within 2%. The Ba3B(Nb, Ta)2O9(B=Sr,Mg,Ca, Hg, Zn, Fe, Ni, Mn, Co, and Ca) materials are found to be semiconductors with a band-gap energy varying from 0.82 to 3.17 eV. A metallic character is observed in Ba3B(Nb, Ta)2O9(B═Ni, Mn, and Co) compounds indicating the presence of conductivity features. A small carrier effective mass indicates the increase of the electron mobility leading to a high n-type conductivity. The p states dominate the lower valence band region. The optical spectra show an anisotropic character between x and z directions. The excitonic effects tend to increase the strength of the oscillator at M0 and M points. The effect is reduced when increasing the photon energy, indicating that the Ba3BB2'O9 compound can be used for devices such as Bragg's reflectors, and optical and optoelectronic devices. The calculations were performed using the BoltzTrap code, which depends on the semi-classical Boltzmann transport equation. The Seebeck coefficient, electrical conductivity, thermal conductivity, power factor, and the figure of merit for Ba3(Fe, Sr, Hg, Zn)B′2O9 are calculated. At higher temperatures, the mobility increases by reducing the electrical conductivity. Ba3(Fe, Sr, Hg, Zn) B2' O9 shows a considerable thermoelectric performance accompanied by a sign point figure of merit larger than many full perovskites reported till date.

Synthesis of Zr substituted B-site complex Bi4(ZrxTi1-x)3O12 platelet microcrystals

Novel plate-like B-site complex Bi4(ZrxTi1-x)3O12 microcrystals consisted with both (Bi2O2)2+ layer and Zr4+substituted [Bi2Ti3O10]2- blocks have been synthesized through molten salt method. With the increase of Zr4+ content, the lattice constant of Bi4(ZrxTi1-x)3O12 increases. From the Raman analysis, the bending vibration was mainly influenced by the Zr4+ content, while both of bending and stretching vibration was influenced at relative high calcination temperature. The reaction conversion process was mainly controlled by the solution-precipitation mechanism and TiO2 provided the basis crystal nucleation in NaCl-KCl molten salt, where the reactant ionic can precipitation, epitaxial growth and finally generated the final bismuth layer-structure products. Finally, fine crystallinity and orientation of plate-like Zr substituted Bi4(Zr0.1Ti0.9)3O12 microcrystals with high aspect ratio can be successful fabricated at 900 °C, which paved a way to design and fabricate the novel plate-like B-site complex perovskite compounds in the future.

Dielectric and electrical characterization of lead-free complex electronic ceramic: (Bi1/2Li1/2)(Zn1/2W1/2)O3

A Lead-free complex perovskite compound of (Bi1/2Li1/2)(Zn1/2W1/2)O3 has been synthesized by using high-temperature solid-state reaction technique. The structural, micro-structural, dielectric constant, tangent loss, electrical impedance, modulus, conductivity and polarization characteristics of the prepared compound have been studied over a wide range of temperature (150–500 °C) and frequency (1 kHz–1 MHz). The X-ray diffraction structural analysis reveals tetragonal structure of the compound with cell parameters; a = 10.6055 (36) A, c = 13.8275 (36) A, c/a = 1.3038 and volume V = 1555.27 A3. The acquired room temperature scanning electron micrograph exhibits the homogeneous distribution of fibre-type of grains throughout the surface of specimen. The dielectric constant and tangent loss of the material at a frequency of 1 kHz are found to be 4000 and 11 respectively. The ac conductivity spectrum provides the information about the conduction mechanism and semiconducting nature of the compound. The impedance spectrum provides an insight into the contributions of grain and grain boundary effects in the resistive and capacitive characteristics of the materials. The frequency dependence of complex modulus analysis shows the presence of non-Debye type of relaxation behaviour in the material.

An insight into the effects of transition metals on the thermal expansion of complex perovskite compounds: an experimental and density functional theory investigation.

ABO3 perovskite-type LaCoO3, LaCo0.5Fe0.5O3, LaCo0.5Ni0.5O3, and LaCo0.5Mn0.5O3 complex oxides were synthesized using the sol-gel method. The microstructure and the thermal expansion behavior of the oxides were investigated. Insights into phonon dispersion and the effects of doped transition metals on thermal expansion were obtained by first-principles calculations based on density functional theory. Thermal expansion coefficients (TECs) at finite temperatures were obtained by quasi harmonic approximation. B-site doping was found to reduce the size of the crystalline grains and the TECs of perovskite compounds. The average TECs of LaCoO3, LaCo0.5Fe0.5O3, LaCo0.5Ni0.5O3, and LaCo0.5Mn0.5O3 were 25 × 10-6 K-1, 11 × 10-6 K-1, 12.5 × 10-6 K-1, and 5 × 10-6 K-1, respectively, in the 0-1000 K temperature range. In addition, the TECs of LaCo0.5Fe0.5O3 and LaCo0.5Ni0.5O3 matched well with those of some common electrolytes.

Microwave dielectric properties of multi-ions Ba(Zn,Ta)O 3-based perovskite ceramics

In this study, Ba(Zn 1/3Ta 2/3)O 3-based complex perovskite compounds, including Ba(Zn 1/3Ta 2/3)O 3, Ba(Zn 1/3Ta 1/3Nb 1/3)O 3, Ba(Zn 1/6Co 1/6Ta 2/9Nb 2/9Sb 2/9)O 3, and Ba 1/2Sr 1/2(Zn 1/6Co 1/6Ta 2/9Nb 2/9Sb 2/9)O 3, were prepared and characterized. There was no second phase formation shown in the XRD patterns. Though it has been suggested that substitutions of multiple ions over A-site or B-site of the Ba(Zn 1/3Ta 2/3)O 3 ceramics may not be beneficial to their microwave dielectric properties, the Ba(Zn 1/6Co 1/6Ta 2/9Nb 2/9Sb 2/9)O 3 and Ba 1/2Sr 1/2(Zn 1/6Co 1/6Ta 2/9Nb 2/9Sb 2/9)O 3 ceramics in this study were found to perform in a fairly acceptable manner. The Ba(Zn 1/6Co 1/6Ta 2/9Nb 2/9Sb 2/9)O 3 ceramic (sintered at 1575 °C for 6 h) and the Ba 1/2Sr 1/2(Zn 1/6Co 1/6Ta 2/9Nb 2/9Sb 2/9)O 3 ceramic (sintered at 1550 °C for 6 h) reported the following characteristics after annealing at 1400 °C for 10 h: 24.9 and 27.0 for dielectric constants ( ɛ r), 83,000 and 32,100 GHz for quality factors ( Q × f) values and −12.8 and −22.6 ppm/°C for temperature coefficients of resonance frequency ( τ f).

Microwave Dielectric Properties of Ca(Li<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3-δ</sub> Ceramics with ZnO Additive

The complex perovskite compound Ca(Li1/3Nb2/3)O3-δ(CLN) ceramics have received much attention due to the superior properties and relatively low sintering temperature 1150°C. In order to further low the sintering temperature of the CLN ceramics, enhance the Q · f values and other dielectric properties, the effects of the additive ZnO on the sinterability and dielectric properties of the CLN have been investigated. The CLN ceramics were prepared by conventional solid state ceramic route. With the addition of 1.0 wt% ZnO, the sintering temperature of Ca(Li1/3Nb2/3)O3-δ(CLN) ceramics was effectively reduced from 1150◦C to 1090◦C，and the Q · f value was increased from 18920 to 20950 GHz (at 7.09 GHz). It also possesses compatible dielectric constant εrof 27.8 and τfvalue of -23.57 ppm/◦C. While with the addition of 1.25 wt% ZnO, the Q · f value of Ca(Li1/3Nb2/3)O3-δ(CLN) ceramics sintered at 1150◦C for 3 hours was increased significantly to 32150 GHz (at 7.09 GHz), εrof 28.3 and τfvalue of -18.55 ppm/◦C. The relationship between microstructure and microwave dielectric characteristics was studied using X-ray diffractometer and Scanning electron microscope.

Ca3WO6: a novel microwave dielectric ceramic with complex perovskite structure

Present work introduces a novel Ca3WO6 microwave dielectric ceramic with a complex perovskite structure. The Ca3WO6 ceramic was prepared by solid state reaction method and can be well densified at above 1,260 °C for 2 h in air. All the XRD patterns can be fully indexed as a single-phase monoclinic structure (space group P21/n). The sharp Raman vibration mode at 810 cm−1 suggests the long range order in the Ca3WO6 structure. The best microwave dielectric properties can be obtained in ceramic sample sintered at 1,275 °C for 2 h with a permittivity ~15.3, a Qf value ~29,200 GHz and a TCF value about −30 ppm/°C. Applying the oxide additivity rule, the calculated permittivity agrees well with the measured value. This kind of ceramic might have some potential value for microwave application for its good microwave dielectric behavior. The (Ca1/2W1/2) complex cations holding the site of Ti4+ in perovskite structure would introduce many new systems in complex perovskite compounds in the future.

Dense Composition with High Q on the Complex Perovskite Compounds

It is clarified in previous paper that high Q depends on high symmetry instead of ordering. The compositions of complex perovskite with high Q were found at composition shifted from ideal one by Koga et al., Kugimiya, and Surendran et al. These data can be summarized as based on Kugimiya's results. The composition located on the tie-line Ba(Mg 1/3 Ta 2/3 )O 3 to BaTa 4/5 O 3 with chemical formula Ba1+α (Mg 1/3 Ta2/3+4α/5V alpha/5) O3+3α. The structure has no defects on A- and O-sites, and the vacancies of Vα/5 with neutrality in the B-site. The density becomes high by resolving of BaTa 4/5 O 3 , because Mg ions are substituted by Ta ions with high weight.

English

The complex perovskite compound CaCu3Ti4O12 (CCTO) is of considerable interest becauseof its anomalously large dielectric response. In this study, the dielectric properties of sol-gel-derived thin films of CCTO prepared at various annealing temperatures; 7000 °C, 7200 °C, and7500 °C have been reported. The frequency and temperature-dependent dielectric properties ofall these samples have been studied in metal-insulator-metal configuration using an impedanceanalyser. Dielectric measurements at room temperature show that the dielectric constant increaseswith the increase in annealing temperature from 700 °C–7500 °C. High dielectric constant (varyingfrom 600 to 3000 with the change in annealing temperature) has been observed at room temperatureat 100 kHz. The dielectric measurements below room temperature do not show any evidence ofstructural relaxation in CCTO except a little additional tilting of the TiO6 octahedra with decreasingtemperature. The dielectric response of Ba-doped CCTO films has also been reported.

Effect of CuO Additives on Sintering and Microwave Dielectric Behaviors of 0.95Ba(Zn1/3Nb2/3)O3–0.05BaZrO3 Ceramics

Microwave dielectric properties of the complex perovskite compound CuO-doped 0.95Ba(Zn1/3Nb2/3)O3–0.05BaZrO3 ceramics have been investigated using the conventional solid state method. Copper oxide effectively lowers the sintering temperature of 0.95Ba(Zn1/3Nb2/3)O3–0.05BaZrO3 ceramics as a sintering aid. Ordering of structures was not observed at sintering temperatures from 1240 to 1360°C. The dielectric constant (εr) saturated at a value of 38–40 from 1270 to 1360°C. The Q×f values of 15000–70000 (at 7 GHz) can be obtained in all cases when the sintering temperatures are in the range of 1240–1360°C. The temperature coefficient of the resonant frequency τf was independent of the sintering temperature. An εr value of 39.7, a Q×f value of 70000 (at 7 GHz), and a τf value of 17 ppm/°C were obtained for 1 wt % CuO-doped 0.95Ba(Zn1/3Nb2/3)O3–0.05BaZrO3 ceramics sintered at 1360°C for 2 h.

Synthesis and Characterization of 0.9PMN-0.1PT Powders by the Use of a Modified Columbite Precursor

The complex perovskite compound 0.9PbMg1/3Nb2/3O3-0.1PbTiO3 is one of the most promising relaxor ceramic because the addition of lead titanate increases Tm by about 5°C/mol% from intrinsic Tm value for pure PMN (near –7 to -15°C). A Ti-modified columbite precursor was used to prepare PMN-PT powders containing single perovskite phase. This variation on columbite route includes Ti insertion in MgNb2O6 orthorhombic structure so that individual PT synthesis becomes unnecessary. Furthermore, effects of Li additive on columbite and PMN-PT structures were studied by XRD to verify the phase formation at each processing step. XRD data were also used for the structural refinement by Rietveld method. The additive acts increasing columbite powders crystallinity, and the amount of perovskite phase was insignificantly decreased by lithium addition. By SEM micrographs it was observed that Li presence in PMN-PT powders leads to the formation of rounded primary particles and for 1mol% of additive, the grain size is not changed, different from when this concentration is enhanced to 2mol%.

Microstructure of Lanthanum Magnesium Niobate at Elevated Temperature

Microstructural studies of the complex perovskite compound La(Mg2/3Nb1/3)O3 (LMN) were conducted using transmission electron microscopy (TEM) and X-ray diffractometry (XRD) at elevated temperatures. 1:1 chemical ordering of B-site cations and tilting of oxygen octahedra were observed in LMN. Three types of superlattice reflections, [1—2]{111}, [1—2]{110}, and [1—2]{100} were observed at room temperature and at 800°C in electron diffraction patterns. In the XRD experiments, the [1—2]{210} and [1—2]{300} extra peaks disappeared at temperatures >1200°C. However, the intensity of the superlattice [1—2]{111} peak did not change with increased temperature up to 1400°C. These results strongly indicated that the origin of superlattice reflection [1—2]{111} was different from that of the other superlattice reflections. It was mainly caused by the 1:1 chemical ordering of magnesium and niobium atoms. The TEM image observed at 800°C showed the ordered domain structures separated by the antiphase boundaries.

Structures and phase transitions in some Pb2B′B″O6 complex perovskite-type compounds

In order to study the influence of substitutions and of the ionic radii of B’ ions on structure and phase transitions, we present some physical measurements and data on Pb2B′B″O6 (B”=W, Nb, Mo) complex perovskite compounds. By Mn and Fe substitution for Mg in Pb2MgWO6 compound a change in lattice parameters and shift of antiferroelectric transition temperature is observed. It appears that in all three series of compounds a linear dependence between ferroelectric or antiferroelectric transition temperature and B’ ionic radii is observed.

Microstructural Characteristics of Strontium Magnesium Niobate

Microstructural studies were conducted on the domain boundaries in Sr(Mg 1/3 Nb 2/3 )O 3 (SMN) complex perovskite compound using X-ray diffractometry and transmission electron microscopy. Both the 1:2 chemical ordering of B-site cations and the tilting of oxygen octahedra were involved in SMN. SMN had a 1:2 ordered monoclinic unit cell, which was distorted by the antiphase tilting of oxygen octahedra. Two types of domain boundaries were found: the antiphase boundaries (APBs), which are not confined crystallographically, and the ferroelastic domain boundaries, which were parallel to the crystallographic planes. SMN had the superlattice reflections of type ±1/6[111] and ±1/2[111] in the electron diffraction patterns, which cannot be indexed in terms of the 1:2 ordered trigonal phase with only a hexagonal unit cell. The presence of the ferroelastic domains that contained both the 1:2 ordered and the antiphase tilting had been verified by a high-resolution transmission electron microscopy lattice image. The structure of SMN was well explained by a model proposed by other researchers. The formation of the 1:2 ordered domains preceded the ferroelastic domains. Normally, the growth of the ferroelastic domain is not affected by APBs, but it is interrupted by them when the driving force for growth is insufficient, resulting in the stoppage of the domains at APBs.

Microstructure Characterizations in Calcium Magnesium Niobate

Microstructural studies on the domain boundaries in Ca(Mg1/3CNb2/3)O3 (CMN) complex perovskite compound were conducted using X‐ray diffractometry and transmission electron microscopy. The 1:2 chemical ordering of B‐site cations and the tilting of oxygen octahedra were involved in the CMN microstructure, as inferred from the presence of two types of domain boundaries. One type was the antiphase boundaries (APBs), which did not lie on a specific set of crystallographic planes. These boundaries were caused by the chemical 1:2 ordering of B‐site cations, magnesium and niobium. The other type was the ferroelastic domain boundaries, which were parallel to a certain crystallographic plane. Therefore, CMN had the 1:2 ordered monoclinic unit cell distorted by the antiphase or in‐phase tilting of oxygen octahedra. CMN had the mixed phases rather than the homogeneous phase.

Structural and dielectric behavior of Pb(Mn1/4Zn1/4W1/2)O3 ceramics

Abstract Polycrystalline complex perovskite compound of Pb(Mn 1/4 Zn 1/4 W 1/2 )O 3 (PMZW) was prepared from a solid-state reaction technique. X-ray powder diffraction (XRD) study suggests the formation of single-phase compound in orthorhombic structure at room temperature. Dielectric studies as a function of temperature (305–573 K) yielded a small dielectric anomaly at 477 K. Variation of dc resistivity as a function of temperature suggests that the compound behaves as the negative temperature coefficient resistors (NTCR). Proper hysteresis loop could not be observed to confirm the ferroelectric behavior.

Relationship between the Bond Valence and the Temperature Coefficient of the Resonant Frequency in the Complex Perovskite (Pb1−xCax)[Fe0.5(Nb1−yTay)0.5]O3

The temperature coefficient of the resonant frequency (TCF) of complex perovskite (Pb1−xCax)[Fe0.5(Nb1−yTay)0.5]O3 ceramics (x= 0.5, 0.55; 0.0 ≤y≤ 1.0) was investigated, relative to the bond valence of the A‐ and B‐site ions in the ABO3 perovskite structure (such as the barium‐, strontium‐, and calcium‐based complex perovskites). The TCF of these complex perovskite compounds varied with the bond valence of the A‐ and B‐sites and the tolerance factor (t) in the perovskite structure. In the tilted region (t < 1.0), the tilting of the oxygen octahedra increased and the TCF decreased, because of the increased bond valence of the B‐site. Also, the dependence of TCF on the bond valence of the A‐site was similar to its dependence on t.