Orthorhombic Pnma Symmetry Research Articles

Optimizing energy storage under low electric field in A-site dysprosium modified BiFeO3-BaTiO3 ceramics

Electric recoverable energy density and dielectric breakdown strength are crucial factors in the high power-density capacitors. This study highlights the A-site dysprosium (Dy) substituted perovskite 0.5(Bi1−xDyx)FeO3-0.5BaTiO3 relaxor ferroelectric ceramics (x = 0–0.30) in O2-atmosphere sintering. An overall pseudo-cubic structure with a major cubic Pm-3m symmetry was observed in all compositions accompanied by multiple lattice symmetries. Anti-polar orthorhombic Pbam space group and non-polar orthorhombic Pnma symmetry gradually increase while ferroelectric tetragonal P4mm symmetry decreases as Dy content approaches x = 0.3. Recoverable energy densities (Wrec) of 4.8 J/cm3 and 3.6 J/cm3, storing efficiencies (η) of 68% and 75%, and recoverable energy storage intensities (ρ) of ∼3.2×10−2 J/kV·cm2 and ∼2.1×10−2 J/kV·cm2 were attained at x = 0 and 0.10 at electric fields of 150 and 175 kV/cm, respectively. The breakdown strength is improved from 150 to 200 kV/cm as x increases from 0.0 to 0.30. This study suggests that grain boundaries and local nanoclusters may act as barriers to inhibit charge transport and consequently increase the breakdown strength.

Effect of heavy rare‐earth substitution on physical properties of BiFeO3 thin films and their photocatalytic application

AbstractHerein, heavy rare‐earth substituted bismuth ferrite thin films were prepared using a low‐temperature sol–gel‐assisted spin coating method. The substitution of heavy rare‐earth ions for Bi3+ leads to structural transformation from rhombohedral (R3c) for x = 0.05 to orthorhombic (Pnma) symmetry for x = 0.05, which was found to have a great effect on the surface morphology, optical band‐gap energy, and photocatalytic activity of a BiFeO3(BFO) thin film. Moreover, the optical properties of prepared films were investigated via UV–visible spectroscopy. For all samples, the bandgap energy values were between 1.18 and 1.65 eV. Moreover, the refractive index and extinction coefficient of samples were about 1.14–1.40 and 0.1–0.6, respectively. Photocatalytic properties of the samples were investigated by measuring the degradation of methylene blue dye under simulated solar irradiation. We found that the heavy rare‐earth substituted BFO thin films have better photocatalytic activity compared to pure BiFeO3 thin film. It was observed that prepared thin films could remove between 37.18% and 77.24% of dye after 180 min irradiation. This study confirms that prepared thin films are a suitable candidate for photocatalytic applications.

The Size Induced Phase Transition in the Rb0.95NbxMo2−xO6.475–0.5x (x=1.31–1.663) Solid Solution with β‐Pyrochlore Structure

AbstractThe size induced phase transition for non‐cubic β‐pyrochlore compounds Rb0.95NbxMo2−xO6.475–0.5x (x=1.31–1.663) has been studied in detail. The Rb0.95NbxMo2−xO6.475–0.5x (x=1.31–1.663) powders with different size particles have been prepared and investigated by X‐ray powder diffraction analysis and scanning electron microscopy with X‐ray microanalysis. The Rb0.95Nb1.5Mo0.5O5.73 and Rb0.95Nb1.375Mo0.625O5.79 powders consisted of ~20 μm crystals possess orthorhombic Pnma symmetry, whereas the same powders with particle size less 1 μm have cubic Fd‐3m and characterized by decreasing Rb content – Rb0.7Nb1.5Mo0.5O5.58 and Rb0.9Nb1.625Mo0.375O5.62. The crystal structure of Rb0.7Nb1.5Mo0.5O5.58 cubic phase refinement has been performed using the Rietveld method; and crystallographic reasons of structure reconstruction have been discussed. The electronic structure and band gap of Rb0.95NbxMo2−xO6.475–0.5x (x=1.31–1.663) compounds have been studied. Moreover the comparison of electronic structure for cubic and orthorhombic phases has been performed.

Origin of Ferroelectricity in BiFeO3-Based Solid Solutions.

We investigate the origin of ferroelectricity in the BiFeO3-LaFeO3 system in rhombohedral R3c and tetragonal P4mm symmetries by ab initio density functional theory calculations and compare their electronic features with paraelectric orthorhombic Pnma symmetry. We show that a coherent accommodation of stereo-active lone pair electrons of Bi is the detrimental factor of ferroelectricity. A Bloch function arising from an indirect Bi_6p-Fe_3d hybridization mediated through O_2p is the primary origin of spontaneous polarization (Ps) in the rhombohedral system. In the orthorhombic system, a similar Bloch function was found, whereas a staggered accommodation of stereo-active lone pair electrons of Bi exclusively results in paraelectricity. A giant Ps reported in the tetragonal system originates from an orbital hybridization of Bi_6p and O_2p, where Fe-3d plays a minor role. The Ps in the rhombohedral system decreases with increasing La content, while that in the tetragonal system displays a discontinuous drop at a certain La content. We discuss the electronic factors affecting the Ps evolutions with La content.

Crystal Structures and Conduction Paths of Sc-Doped CaTiO3 Fast Oxide-Ion Conductors with Orthorhombic Symmetry

The crystal structures and electron density distributions (EDDs) of Ca-deficient Sc-doped CaTiO3 fast oxide-ion conductors, Ca0.97(Ti0.97Sc0.03)O3-δ (CTS3) and Ca0.96(Ti0.9Sc0.1)O3-δ (CTS10), were investigated in the temperature range of 298-1173 K in N2 to analyze the effect of composition on the perovskite structure and oxide-ion transport mechanism. CTS3 and CTS10 exhibited orthorhombic Pnma symmetry in temperature ranges of 298-1173 K and 973-1173 K, respectively, with CTS10 exhibiting lower symmetry and reduction in oxide-ion conductivity below 973 K. The EDDs of CTS3 and CTS10 at 1173 K indicated unique chemical bonds and conduction paths. CTS3 and CTS10 showed covalent bonds between (Ti,Sc) and O1 (or O2) sites. CTS3, with a lower oxide-ion conductivity than that of CTS10, exhibited pseudo-one-dimensional (1D) zig-zag curved conduction paths for oxide-ions along the a-axis, unlike previously reported curved migration paths along the b-axis in CaTiO3, and chemical bonds between Ca and O1 sites, indicating oxide-ion conduction suppression. In CTS10, additional conduction paths were observed along the a-axis, forming three-dimensional (3D) zig-zag curved conduction paths in the ac-plane and along the b-axis, with the weakening of the chemical bonds between the Ca and O1 sites. The oxide-ion conductivity and mobile oxide-ion concentration of CTS10 were 3.6 and 2.0 times those of CTS3, respectively, at 1173 K; the higher oxide-ion conductivity of CTS10 could be attributed to an increase in the mobile oxide-ion concentration and mobility with a 1D to 3D change in the conduction paths and a weakening of chemical bonds between the Ca and O1 sites.

Effect of Heat Treatment on Structural, Magnetic and Electrical Properties of La2FeMnO6.

In this study, the effect of heat treatment on the structural, magnetic and electrical properties of La2FeMnO6 prepared via the sol–gel and sintering method were investigated. The heat-treatment conditions, i.e., the calcination temperature (1023 K and 1173 K), sintering temperature and time (1273 K for 1 and 3 h) were carried out. X-ray diffraction (XRD) revealed orthorhombic pnma (62) symmetry without any impurity phase for all samples. X-ray photoelectron spectroscopy confirmed the presence of Fe2+–Fe3+–Fe4+ and Mn3+–Mn4+ mixed states, and lanthanum and oxygen vacancies resulting in various magnetic exchange interactions. Furthermore, the magnetisation hysteresis showed enhanced hysteresis loops accompanied by an increase in magnetisation parameters with calcination temperature. The Raman phonon parameters induced a redshift in the phonon modes, alongside an increase in the intensity and compression of the linewidth, reflecting a decrease in lattice distortion, which was confirmed by XRD. The temperature-dependent conductivity showed that the conduction mechanism is dominated by p-type polaron hopping, and the lowest activation energy was approximately 0.237 ± 0.003 eV for the minimum heat-treatment conditions. These results show that varying heat-treatment conditions can significantly affect the structural, magnetic and electrical properties of the La2FeMnO6 system.

Nitro-sonium tetra-fluorido-borate, NOBF4.

The crystal structure of oxido-nitro-gen(1+) tetra-fluorido-borate (nitro-sonium tetra-fluorido-borate), NO+BF4 -, was refined on the basis of single-crystal X-ray diffraction data at 150 K. The compound crystallizes in the baryte structure type with ortho-rhom-bic Pnma symmetry. The crystal structure exhibits cationic disorder with equal occupation of N and O atoms at the same site.

Structural, optical, and electrical properties of alkaline earth doped La2-xAxFeMnO6 (A = Ca, Sr, and Ba) double perovskites

The polycrystalline double perovskites La2-xAxFeMnO6 (A = Ca, Sr, Ba; x = 0.0, 0.4) were synthesized through citrate sol-gel auto-combustion technique. The structural, optical, and electrical properties were studied by x-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy at room temperature, while electrical and dielectric measurements were evaluated at temperature ranges from 303 to 423 K. The XRD analysis through Rietveld refinement suggests the single phase orthorhombic (Pnma) symmetry for all the synthesized samples. The infrared reflectivity (IR) spectra were obtained from Fourier Transform Infrared spectroscopy (FTIR) measurements. The spectra were fitted by Lorentz oscillator model, to observe the optical phonon modes. The activation energies were calculated by DC resistivity measurements. According to the resistivity measurement the samples shows the semiconducting nature. The temperature dependent dielectric constant and tangent-loss with varying frequency are measured and discussed.

Effects of neodymium substitution on the structural, optical, and magnetic properties of yttrium iron garnet nanoparticles

Neodymium (Nd3+)-doped yttrium iron Garnet (YIG) nanoparticles, with compositional variation of NdxY3−xFe5O12 (0.0 ≤ x ≤ 3.0), were prepared by co-precipitation method. The prepared nanoparticles were characterized using TGA, XRD, TEM, SEM, EDX, and FTIR. The calcination temperature was chosen according to the maximum decomposition temperature (˃ 810 °C) achieved in TGA. XRD confirmed the successful phase formation, at the chosen sintering temperature (1100 °C), of Garnet for x < 3.0 (cubic Ia3d symmetry), after which the orthoferrite phase NdFeO3 at x = 3.0 (orthorhombic Pnma symmetry) was formed. The incorporation of Nd3+ increased the lattice parameters (12.3833–12.5020 A), porosity (34.127–39.549%) and crystallite size (82.66–129.99 nm). Agglomerated, distorted, and irregularly shaped nanoparticles were observed in TEM and SEM with the elemental composition confirmed by EDX, inconsistency with the proposed NdxY3−xFe5O12. The FTIR analysis revealed the characteristic bands at 657, 600, and 565 cm−1 with Nd3+ doping concentration between 0.0 and 1.5. These bands disappeared at x = 3.0, where the orthoferrite phase of NdFeO3 dominated. UV–Vis spectroscopy revealed the semiconducting behavior of the prepared samples with energy gaps ranging between 2.89 and 3.02 eV. A broad emission band was observed, in the range 500–550 nm, in the PL spectra of all the prepared samples in agreement with the calculated band energies. The transport properties were studied by DC conductivity measurements and analyzed by the Arrhenius plots, from which two activation energies were determined for each sample. The magnetic properties, investigated by VSM, showed that isovalent substitution of Y3+ by Nd3+ dramatically influenced room temperature parameters, such as saturation magnetization, coercivity, and remanence magnetization.

Structure and physical properties of SeCo1−xMnxO3

We describe the high-pressure (4 GPa) high-temperature (∼1100 K) synthesis of the solid solution series SeCo1−xMnxO3 (0 < x < 1) using H2SeO4 and transition metal oxide mixtures sealed in Pt capsules. Neutron powder diffraction has been performed to determine progression of the structure across the solution. All samples crystallise with orthorhombic Pnma symmetry, and octahedral tilting is determined to increase with Mn content. SQUID magnetometry measurements were performed, and reveal that the Néel temperature shifts only by approximately 1 K over the series.

Ultrahigh Energy‐Storage Density in NaNbO3‐Based Lead‐Free Relaxor Antiferroelectric Ceramics with Nanoscale Domains

AbstractDielectric energy‐storage capacitors have received increasing attention in recent years due to the advantages of high voltage, high power density, and fast charge/discharge rates. Here, a new environment‐friendly 0.76NaNbO3–0.24(Bi0.5Na0.5)TiO3 relaxor antiferroelectric (AFE) bulk ceramic is studied, where local orthorhombic Pnma symmetry (R phase) and nanodomains are observed based on high‐resolution transmission electron microscopy, selected area electron diffraction, and in/ex situ synchrotron X‐ray diffraction. The orthorhombic AFE R phase and relaxor characteristics synergistically contribute to the record‐high energy‐storage density Wrec of ≈12.2 J cm−3 and acceptable energy efficiency η ≈ 69% at 68 kV mm−1, showing great advantages over currently reported bulk dielectric ceramics. In comparison with normal AFEs, the existence of large random fields in the relaxor AFE matrix and intrinsically high breakdown strength of NaNbO3‐based compositions are thought to be responsible for the observed energy‐storage performances. Together with the good thermal stability of Wrec (&gt;7.4 J cm−3) and η (&gt;73%) values at 45 kV mm−1 up to temperature of 200 °C, it is demonstrated that NaNbO3‐based relaxor AFE ceramics will be potential lead‐free dielectric materials for next‐generation pulsed power capacitor applications.

Effects of external magnetic field and hydrostatic pressure on magnetic and structural phase transitions in Pr0.6Sr0.4MnO3

We investigate the effect of hydrostatic pressure on the temperature dependence of magnetization and also the influence of magnetic field on the linear thermal expansion in polycrystalline Pr0.6Sr0.4MnO3, which is ferromagnetic at room temperature (TC = 305 K) but its magnetization undergoes an abrupt decrease at TS = 89 K within the ferromagnetic state. Normal and inverse magnetocaloric effects around TC and TS, respectively, were reported earlier in this single phase compound [Repaka et al., J. Appl. Phys. 112, 123915 (2012)]. The thermal expansion shows an abrupt decrease at TS in zero magnetic field but transforms into an abrupt increase at the same temperature under 7 T, which we interpret as a consequence of magnetic field-induced structural transition from the low-temperature monoclinic (I2/a symmetry) to high-temperature orthorhombic (Pnma symmetry) phase in corroboration with a published neutron diffraction study in zero magnetic field. While the external magnetic field does not change TS, the application of a hydrostatic pressure of P = 1.16 GPa shifts the magnetic anomaly at TS towards high temperature. The pressure induced shift of the low-temperature magneto-structural anomaly (ΔTS = 27 K) is nine-times higher than that of the ferromagnetic Curie temperature (ΔTC = 3 K). Our results suggest that while the hydrostatic pressure stabilizes the low temperature monoclinic phase at the expense of the orthorhombic phase, the applied magnetic field does not affect the structural transition temperature.

Evolution of structural and magnetic phases in Nd doped BiFeO3 multiferroics with sintering time

The effect of sintering time on the evolution of structural and magnetic phases has been studied in Bi0.8Nd0.2FeO3 multiferroic. These multiferroics were prepared by normal solid state reaction technique. XRD, NPD and VSM characterizations were performed to explore the structural and magnetic properties and correlation between these. The refinement of the XRD patterns using FullProf program show, mixed phase having rhombohedral (R3c)+orthorhombic (Pnma) symmetry in sample sintered for 1h. For sample sintered for two hours, crystal structure was found to be mixed phase with rhombohedral (R3c)+orthorhombic (Pbam) symmetry and the sample sintered for three hours, it crystallized in pure orthorhombic (Pbam) symmetry. The octahedral tilting is thus found to be changing systematically with the variation of sintering time. The refinement of the neutron diffractions patterns confirms the XRD results of structural evolution with sintering time. The magnetic moment undergoes change in the direction of their preferential alignment from c-axis to along a-axis in the 3h sintered sample. The M-H loops shows significant enhancement in magnetization from 0.17455emu/g to 0.35872emu/g with increase in sintering time from 1 to 3h. The enhancement in the magnetization is attributed to increase in the canting angle between magnetic spins. Also, the observation of exchange bias effect with discontinuous variation in exchange bias field indicates the presence of magnetic anisotropy. The magnetic moments obtained through the magnetic refinement of NPD patterns are found to decrease from 4.6 μB to 3.8 μB with increase in sintering time from 1 to 3h.

Crystal structure transformation and improved dielectric and magnetic properties of La-substituted BiFeO3 multiferroics

Abstract Samples of Bi 1−x La x FeO 3 with x = 0.1, 0.3, 0.5, and 0.7 have been synthesized by two stage solid state reaction method. Structural characterization was performed using powder x-ray diffraction at room temperature. The crystal structure of perovskite phases are further characterized via Rietveld analysis which revealed a structural transition from R 3 c symmetry of the parent phase of BiFeO 3 to orthorhombic Pnma symmetry of LaFeO 3 . However the intermediate samples with x = 0.3 and 0.5 are bi – phasic (i.e. a combination of rhombohedral R 3 c and orthorhombic Pbam phases co-exist). Rietveld Refinement presents a good agreement between measured and simulated patterns. The transition from a rhombohedral to orthorhombic unit cell is suggested to be driven by the dilution of the stereochemistry of the lone pair of Bi 3+ at A- site. M-H hysteresis loops are recorded at room temperature up to a field of 15 kOe. The G-type antiferromagnetic spin structure and the magnetic moment are very sensitive to increasing La concentration at A-site. La substitution transformed antiferromagnetic BiFeO 3 into ferromagnetic which is closely related to the structural phase transition and modification of antiparallel spin structure. Dielectric constant (e′) and dissipation factor (tan δ) measured in frequency range 1 kHz to 5 MHz showed dispersion behaviour at low frequencies.

Phase Diagram of BiFeO3/LaFeO3 Superlattices: Antiferroelectric‐Like State Stability Arising from Strain Effects and Symmetry Mismatch at Heterointerfaces

(BiFeO3)(1−x)Λ/(LaFeO3)xΛ superlattices (SLs) have been grown using pulsed laser deposition and studied by X‐ray diffraction, transmission electron microscopy (TEM), and Raman spectroscopy. The composition is varied, 0.30 ≤ x ≤ 0.85, while the modulation period Λ is kept constant at about 10 nm. Unit cell doubling signatures typical of orthorhombic Pnma symmetry for x = 0.80 and 0.85 SLs and ¼{011} antiferroelectric PbZrO3‐like reflections in SLs with 0.30 ≤ x ≤ 0.7 are detected by TEM showing a complex structural mixture at the nanoscale level. The Raman spectra confirm these observations and show a change in the SLs from a Pnma LaFeO3‐like spectra for LaFeO3‐rich period to a PbZrO3‐like spectra for BiFeO3‐rich period. Electron–phonon interactions and resonant‐like excitations are also observed in the SLs. A temperature‐dependent X‐ray diffraction investigation shows a large shift of the paraelectric‐antiferroelectric phase transition scaling with the BiFeO3 thickness. This shift is correlated with the strain state and can be explained by a strong interplay between octahedral rotation/tilt and antipolar Bi displacement. Thickness–temperature phase diagram is constructed and differs from previous report showing the extreme sensitivity of the BiFeO3 phase stability to strain effects and rotation/tilt degrees of freedom.

Impact of silver substitution on the magnetotransport and thermal behavior of polycrystalline Sm0.55Sr0.45−xAgxMnO3 (x = 0 & 0.15) manganites

We have synthesized a series of Sm0.55Sr0.45−xAgxMnO3 (x = 0 & 0.15) by conventional solid state reaction method to scrutinize the effect of monovalent Ag+ as a replacement of Sr2+ ion on structural, electrical, magnetotransport and thermoelectric properties. The structural parameters obtained using Rietveld refinement of X-ray diffraction data which showed perovskite structure having orthorhombic (Pnma) symmetry without any detectable impurity phase. It is observed that MZFC and MFC curves become more manifested as Ag+ content is increased which indicates an increase in magnetic frustration arising due to bending of Mn-O-Mn bond. The M-H plots show the narrow hysteresis loops which indicate the soft ferromagnetic nature. Magnetic studies also show that the Curie temperature TC is found to decrease with Ag+ content. The metal–insulator transition temperature (TMI) is observed which decreases with the increase of Ag+ content when magnetic field is applied. The resistivity data in high temperature region are explained within the framework of variable range hopping (VRH) and small polaron hopping (SPH) models. The thermoelectric power (S) of the reported samples exhibits a crossover from positive to negative value and value of S increases in doped samples. The analysis of thermoelectric power data confirms that the small polaron hopping model in high temperature region and at low temperature electron–magnon scattering is the dominating in the FM region. With increasing the Ag+ content the samples showed very high magneto-resistance (MR%) and temperature coefficient of resistance (TCR%) which make the compound more promising for scientific and technological applications.

Characterization of B site codoped LaFeO3 nanoparticles prepared via co-precipitation route

LaFe1−x−y Co x Pd y O3 [(x, y) = (0, 0), (0.40, 0), (0.38, 0.05)] nanoparticles were synthesized via a co-precipitation route using ammonium hydroxide, sodium hydroxide and ammonium carbonate as the precipitant and calcination at different temperatures to study the compositional driven structural changes in lanthanum ferrites. Analysis of X-ray diffraction (XRD) patterns confirms the formation of single-phase perovskite structure and existence of orthorhombic Pnma symmetry for calcined powders. Field emission scanning electron microscope (FESEM) observations show that Pd-doped powders yield finer particles along with narrower particle size distribution compared with LaFeO3 and LaFe0.6Co0.4O3. Moreover, using ammonia as the precipitant leads to a smaller mean particle size of powders compared to NaOH, as well as significant difference in morphology of the particles. Raman analysis reveals that both Co and Pd atoms substitute Fe site in perovskite structure with shifting of phonon modes. Comparing Raman spectra demonstrates the presence of more oxygen vacancies in Pd-doped perovskites. It can be concluded from the results that Pd is successfully incorporated into the perovskite structure by co-precipitation method.

Crystallographic features of orbital ordering related to the C-type antiferromagnetic state in the simple perovskite manganite Ca1-xPrxMnO3

ABSTRACTIn the highly-correlated electronic system Ca1-xPrxMnO3 having the simple perovskite structure, it has been reported that there exists the C-type orbital-ordered (COO) state accompanying an antiferromagnetic ordering for 0.10 ≤ x ≤ 0.25. According to the previous studies concerning orbital-ordered states in simple perovskite manganites, the COO state was understood to be characterized by a spatial array of (3z2-r2)-type orbitals for 3d electrons in Mn ions. The notable feature of the COO state in Ca1-xPrxMnO3 is that the state with the monoclinic-P21/m symmetry appears as a result of the structural transition from the disordered state with the orthorhombic-Pnma symmetry. Compared with the COO-state formation from the cubic-Pm$\overline 3$m state, however, the formation from the disordered-Pnma state has not been understood yet. We have thus examined the crystallographic features of the formation of the COO state in Ca1-xPrxMnO3, mainly by x-ray powder diffraction and transmission electron microscopy. In the case of x = 0.16, for instance, the COO state was found to appear from the disordered-Pnma state around 90 K on cooling. The notable feature of the formation is that, in the Pnma state just before the COO-state formation, characteristic diffuse scattering appeared around each reflection in electron diffraction patterns, together with the splitting of the 200c reflection in x-ray powder diffraction profiles in the pseudo-cubic notation. Based on these experimental data, it is understood that the formation of the COO state in Ca1-xPrxMnO3 accompanies remarkable fluctuations of the C-type orbital ordering in the disordered-Pnma state.

Antisymmetric exchange in La-substituted BiFe0.5Sc0.5O3 system: symmetry adapted distortion modes approach

Abstract Neutron powder diffraction measurements on the 35 % La-substituted Bi1−x La x Fe0.5Sc0.5O3 composition revealed that the samples obtained under high-pressure (6 GPa) and high-temperature (1500 K) conditions crystalize into a distorted perovskite structure with the orthorhombic Pnma symmetry and the unit cell parameters: a o = 5.6745(2) Å, b o = 7.9834(3) Å and c o = 5.6310(2) Å. A long-range magnetic ordering takes place below 220 K and implies a G-type magnetic structure with the moments 4.10(4)μ B per Fe aligned predominately along the orthorhombic c-axis. The space group representation theory using the orthorhombic symmetry yields four bi-linear coupling schemes for the magnetic order parameters imposed by antisymmetric exchange interactions. The couplings are analysed based on symmetry adapted distortion modes defined in respect of the undistorted cubic perovskite structure. The approach allows a quantitative estimation of the coupling strength. It is shown that the experimentally found spin configuration combines the magnetic order parameters coupled by the atomic displacement modes with the largest amplitudes. The results indicate that the antisymmetric exchange is the dominant anisotropic term which fully controls the direction of the Fe3+ spins in the distorted perovskite lattice.

New low loss A9B9O31 (A = La; B = Ti, Mg, Sc, Fe, Al, Ga) ceramics for microwave applications

AnBnO3n+2 (n = 4.5) type layered perovskite ceramics with general formula A9B9O31 (A = La; B = Ti, Mg, Sc, Fe, Al, Ga) were prepared via a mixed oxide solid state sintering route. X-ray diffraction analysis revealed single phase La9(TiB)9O31 (B = Ti, Mg, Sc, Fe, Al, Ga) solid solutions with orthorhombic (Pnma) symmetry when sintered at 1500–1650 °C for 4–12 h. The temperature coefficient of resonance frequency (τf) was influenced by the polarizability of B-site cations while relative permittivity (εr) and quality factor (Q × fo) were dependent on the relative density. The samples investigated in the present study exhibited reasonable εr (39–48.3), high Q × fo (11823–19070 GHz) and near zero τf (−1.28 to −22.16 ppm/°C). These ceramics might be potential candidates for microwave devices.