Orthorhombic Perovskite Phase Research Articles

Preparation and characterization of Ba-doped LaFeO3 nanofibers by electrospinning and their ethanol sensing properties

Uniform Ba-doped LaFeO3 nanofibers (NFs) with pure orthorhombic perovskite phase were successfully fabricated by electrospinning and subsequent calcination, and their ethanol sensing properties were investigated for the first time. The characterized results reveal that the well-crystallized La1−xBaxFeO3 (x ≤ 0.3) NFs consist of a large amount of interconnected nanocrystals with the mean sizes of about 20–35 nm, and there are plenty of voids distributed between the nanoparticles within the NFs. Gas sensing investigations indicate that the sensors based on La1−xBaxFeO3 NFs exhibit considerable sensitivity to ethanol gas and the response of sensors first increases and then decreases with the increase of Ba doping content. Among those sensor, the sensor based on La0.75Ba0.25FeO3 NFs shows the best response. To 500 ppm of ethanol gas, the highest response for the La0.75Ba0.25FeO3 NFs based sensor reaches 136.1 at a lower optimum operating temperature of 210 °C compared to the La0.75Ba0.25FeO3 powder sensor, and the corresponding response and recovery times are about 42 and 40 s, respectively. Meanwhile, it shows good stability and selectivity to ethanol gas. Our results demonstrate that the as-prepared Ba-doped LaFeO3 NFs can be a promising candidate for good performance ethanol sensors.

Further optimization of barium cerate properties via co-doping strategy for potential application as proton-conducting solid oxide fuel cell electrolyte

Yttrium-doped BaCeO3 is one of the most promising electrolyte candidates for solid oxide fuel cells because of its high ionic conductivity. Nd and Y co-doped BaCeO3 strategy is adopted for the further optimization of Y-doped BaCeO3 electrolyte properties. X-ray diffraction results indicate that the structure of BaCe0.8Y0.2-xNdxO3-δ (x = 0, 0.05, 0.1, 0.15) with orthorhombic perovskite phase becomes more symmetric with increasing Nd concentration. The scanning electron microscope observation demonstrates that the densification and grain size of the sintered pellets significantly enhance with the increase of Nd doping level. Whether in dry and humid hydrogen or air, the increase of Nd dopant firstly increases the conductivities of BaCe0.8Y0.2-xNdxO3-δ (x = 0, 0.05, 0.1, 0.15) and then decrease them after reaching the peak value at x = 0.05. Electrochemical impedance spectra at 350 °C can distinguish clearly the contribution of grain and grain boundary to total conductivity and the highest conductivity of BaCe0.8Y0.15Nd0.05O3-δ ascribes to the decrease in bulk and grain boundary resistances due to the synergistic effect of Nd and Y doping. The anode-supported single cell with BaCe0.8Y0.15Nd0.05O3-δ electrolyte shows an encouraging peak power density of 660 mW cm−2 at 700 °C, suggesting that BaCe0.8Y0.15Nd0.05O3-δ is a potential electrolyte material for the highly-efficient proton-conducting solid oxide fuel cell.

High-Pressure Synthesis, Crystal Structure, and Magnetic and Transport Properties of a Six-Layered SrRhO3.

A SrRhO3 polytype with six-layered (6M) structure was synthesized under high pressure and high temperature. The crystal structure was obtained by refining X-ray powder diffraction with the monoclinic space group C2/c with lattice parameters a = 5.5650(1) Å, b = 9.5967(2) Å, c = 14.0224(4) Å, and β = 92.846(2)°. It is isostructural with SrIrO3 synthesized under ambient pressure and consists of dimers of the face-shared Rh(2)O6 octahedra connected by their vertices to the corner-shared Rh(1)O6 octahedra along the c axis with a stacking of SrO3 layers in the sequence of CCHCCH, where C and H denote cubic and hexagonal closed packing, respectively. With increasing pressure, the 6M SrRhO3 transforms to an orthorhombic perovskite (Pv) phase, having a = 5.5673(1) Å, b = 5.5399(2) Å, c = 7.8550(2) Å in the space group Pbnm. A pressure-temperature phase diagram shows that the 6M-Pv phase boundary moves to lower temperatures with increasing pressure. Both the 6M and the Pv phases of SrRhO3 were characterized by magnetic susceptibility, resistivity, and thermopower; they are all metals with an enhanced and temperature-dependent magnetic susceptibility; no long-range magnetic order has been found. The polytype structures are normally found in ABO3 oxides with the geometric tolerance factor t > 1. SrRhO3 represents another example (in addition to SrIrO3) where the polytype 6M structure can be stabilized with a t < 1.

Synthesis and characterization of bi-component ZnSnO3/Zn2SnO4 (perovskite/spinel) nano-composites for photocatalytic degradation of Intracron Blue: Structural, opto-electronic and morphology study

Bi-component ZnSnO3/Zn2SnO4 nano-composites was prepared from zinc chloride and tin (IV) chloride tetrahydrate via a simple co-precipitation method. X-ray diffraction (XRD), Fourier transform infrared (FT-IR), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), thermo-gravimetric analysis (TG-DTG) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) were used to study crystal structure, opto-electronic, thermal and morphological properties of nano-composite. XRD patterns indicated the presence of ZnSnO3 orthorhombic perovskite and Zn2SnO4 cubic inverse spinel phase in nano-composite with no diffraction peaks of the ZnO or SnO2 phases. UV–vis DRS results showed a good absorbance in UV region of solar light with optical band gap of 3.33eV. FESEM results showed the nano-composite with diameter of 38nm. Crystalline ZnSnO3/Zn2SnO4 nano-composite exhibited good photo-catalytic activity to Intracron Blue dye degradation under UV illumination.

Structural and morphological analysis of barium cerate electrolyte for SOFC application

AbstractGadolinium doped barium cerate (BCG) electrolytes Ce0.8Gd0.2O1.9+ xBaO (x = 0.1 and 0.4) were prepared by wet chemical method for the use in solid oxide fuel cells operating at intermediate temperatures (600 °C to 800 °C). The as-prepared powder sample was calcined at 900 °C. The calcination temperature was identified using differential scanning calorimetry (DSC) analysis. The orthorhombic perovskite phase formation was confirmed by XRD analysis. From TEM results, the particle size was found to be about 32 nm which is in a good agreement with XRD results. BCG nanoparticles were formed at lower sintering temperature due to using microwave furnace. By reducing the sintering temperature of solid electrolyte through microwave technique, the percentage of barium loss was successfully reduced and the prepared electrolyte can be a good choice for solid oxide fuel cells operating at intermediate temperatures.

Improvement in structural, dielectric and energy-storage properties of lead-free niobate glass-ceramic with Sm2O3

Phase evolution, microstructure, dielectric performance, polarization, breakdown strength as well as energy-storage behaviors for the lead-free niobates glass-ceramics with Sm2O3 were systematically investigated. Two crystallographic structures of tetragonal tungsten bronze and orthorhombic perovskite complex phases were obtained and Sm3+ entered into the crystalline phases. The optimal microstructure of the glass-ceramic was obtained with Sm2O3 of 2mol%. Both dielectric constant and polarizability were enhanced with increasing Sm2O3. The breakdown strength and energy-storage behaviors of the glass-ceramics were also improved by increased Sm2O3. The highest breakdown field of 21.2kV/mm, the highest charged (0.74J/cm3) and discharged energy density (0.45J/cm3) were obtained in the glass-ceramic with 2mol% Sm2O3. It is due to the reduced interfacial polarization in this particular composition.

One-step hydrothermal synthesis of LaFeO3 perovskite for methane steam reforming

This work describes the synthesis of LaFeO3 oxide, using a one-step hydrothermal synthesis route, to obtain a solid with useful superficial, morphological and textural properties for applications in steam methane reforming reaction. The synthesis process starts from the corresponding metal nitrates of lanthanum and iron dissolved in deionized water in well-defined concentration, and the dissolution of KOH as mineralizing agent. The reaction is developed in a Teflon-lined stainless steel autoclave at 300 °C for 14 days. The composition and surface area were determined with X-ray fluorescence and nitrogen adsorption isotherms, confirming the basic stoichiometry of oxide and a high active area. The crystalline structure was evaluated with X-ray diffraction analysis, showing a pure orthorhombic perovskite phase. Temperature programmed reduction results show the development of three single steps at different temperatures, kinetically detectable and related with reduction of component oxides. Scanning and transmission electron microscopy results, showed a remarkable degree of crystallization, favoring a specific morphology as result of the low consolidation temperature of the perovskite phase. The catalytic test, analyzed by means of steam methane reforming action, performed along 240 h on stream, reveals a light deactivation rate, decreasing progressively 7.1 % until 60 % of methane conversion, indicating the improved morphological and surface characteristics of solid for potential applications.

LiNbO3-Type InFeO3: Room-Temperature Polar Magnet without Second-Order Jahn–Teller Active Ions

Great effort has been devoted to developing single-phase magnetoelectric multiferroics, but room-temperature coexistence of large electric polarization and magnetic ordering still remains elusive. Our recent finding shows that such polar magnets can be synthesized in small-tolerance-factor perovskites AFeO3 with unusually small cations at the A-sites, which are regarded as having a LiNbO3-type structure (space group R3c). Herein, we experimentally reinforce this finding by preparing a novel room-temperature polar magnet, LiNbO3-type InFeO3. This compound is obtained as a metastable quench product from an orthorhombic perovskite phase stabilized at 15 GPa and an elevated temperature. The structure analyses reveal that the polar structure is characterized by displacements of In3+ (d10) and Fe3+ (d5) ions along the hexagonal c-axis (pseudocubic [111] axis) from their centrosymmetric positions, in contrast to well-known perovskite ferroelectrics (e.g., BaTiO3, PbTiO3, and BiFeO3) where d0 transition-metal ion...

Characterization of Proton-Conducting Y(CrO4)1-X (PO4) x As a Cathode Material of Proton-Conducting Ceramic Fuel Cells

It has been reported that proton conducting oxide such as BaCeO3 and BaZrO3 have high proton conductivity at intermediate temperatures, IT, around 400-600°C. Therefore, proton-conducting ceramic fuel cells (PCFC) attract much attention as IT-operating fuel cell system (IT-FC). Nonetheless, the current PCFC performance lags far behind the SOFC performance even at the ITrange of 400-600°C. One of the reasons for the deteriorated performance of PCFC is the lack of suitable cathode materials. Generally, oxide ion-electron mixed conductors such as La0.6Sr0.4Co0.8Fe0.2O3- δ(LSCF) are used for the PCFC cathode, but these reveal large overpotential since forming the limited reaction zone due to the mismatch of ionic carriers with electrolyte. Accordingly, there is motivation to develop the proton-electron mixed conductors which can be used in cathode conditions of fuel cells. Previously, we found that Y(CrO4)1-x (PO4) x solid solution (YCP) have proton-electron mixed conductivity in wet air atmosphere. Hence, it is motivated to use YCP as additives of cathode materials of PCFC in order to extend the reaction zone. In this work, we examined the fuel cells using composite cathode of YCP and LSCF. BaCe0.7Zr0.1Y0.2O3- δ(BZCY) was used as proton conducting electrolyte. Bulk electrolyte cell were constructed with a BZCY disc which were prepared by solid state reactive sintering (SSRS) method. The electrolyte precursor powder was prepared by mixing proper amount of BaCO3, CeO2, ZrO2, and Y2O3 according to the desired stoichiometry with the addition of 2.0wt.% NiO as a sintering aid. This mixture was ball-milled for 48 h and uniaxially pressed under 20 MPa for 1 min and then cold-isostatic-pressed under 100 MPa for 1 min. Finally, the green pellets were calcined at 1400°C for 18 h so as to obtain bulk electrolyte disc (2 mmd, 9 mmf). YCP powders were synthesized by pyrolysis of the mixed Y-Cr-P hydroxide precursor at 700°C for 3h in O2. The hydroxide precursors were prepared by coprecipitation method with (NH3)H2PO4, Cr(NO3)3 and Y(NO3)3. YCP powders dispersed in a-Terpineol were mixed with LSCF paste (NexTek) in the volume ratio of YCP:LSCF = 1:1. YCP-LSCF mixed pastes were screen printed on the side of BZCY electrolyte as a cathode and Pt paste as anode was applied to the opposite faces so as to form Pt|BZCY|YCP5/LSCF cell. Au wire was attached along the side of BZCY disc as a reference electrode by using Au paste. To investigate cathode polarization characteristics, the complex impedance measurements were carried out with the three-electrode cell. The XRD pattern indicated that a single orthorhombic perovskite phase of BZCY was prepared by the SSRS method. The density of the sintered pellets was about 90%. The bulk electrolyte cell with the YCP5/LSCF cathode gives OCV over 1.0 V and maximum power density about 40 mW cm-2 at 600°C. The complex impedance measurements indicate that the cells reveal two impedance arcs according to cathodic polarization in Nyquist plots. The semicircle appearing in high frequency region (104-102 Hz), SH, can be assigned to the charge transfer reaction between the electrolyte and the cathode and one in low frequency region (102-10-1 Hz), SL, can be attributed to the dissociative oxygen adsorption reaction. SH of the cell with YCP-LSCF composite cathode was smaller than that of the cell with LSCF cathode. On the other hand, the SL of the composite cathode cells was larger than that of the LSCF cathode cells. These results indicate that the interfacial charge transfer reaction is promoted by adding proton-conducting YCP because of the extension of the electrode-electrolyte-air three phase boundary.

Novel solar absorptive and infrared reflective properties of Cu-doped Sm0.5Sr0.5CoO3−δ

Cu2+ doped Sm0.5Sr0.5CoO3−δ perovskite oxides were synthesized via the conventional solid state reaction method. The effect of Cu doping concentration on composition, electrical conductivity, solar absorbance and infrared emittance of Sm0.5Sr0.5Co1−xCuxO3−δ were investigated. It was found that the structure of the samples was orthorhombic perovskite phase. The second phase SrCoO2.8 was detected in the samples with Cu doped concentration for x = 0.2–0.5. The electrical conductivity decreased due to the substitution of Co3+ ion by Cu2+ ion decreasing the overlapping of Co 3d orbital and O 2p orbital and influencing the effective electron transfer from Co3+ ion to Co4+ ion. In addition, the optical properties of the samples were discussed, and the results showed the thermal emittance increased gradually from 0.29 to 0.74 and the solar absorbance changed slightly from 0.70 to 0.88 with increased Cu2+ doping. These results indicate the oxides Sm0.5Sr0.5Co1−xCuxO3−δ have a good application prospect in the field of solar energy.

Thermodynamic stability of mixed Pb:Sn methyl‐ammonium halide perovskites

AbstractUsing density functional theory, we investigate systematically mixed perovskites, where is , and is , , or . Ab initio calculations of the orthorhombic, tetragonal, and cubic perovskite phases show that the substitution of lead by tin has a much weaker influence on both structure and cohesive energies than the substitution of the halogen. The thermodynamic stability of the mixtures at finite, non‐zero temperatures is studied within the regular solution model. We predict that it will be possible to create mixtures at any temperature. Our results imply that mixing is unlikely for the low‐temperature phase of bromide and chloride compounds, where instead local clusters are more likely to form. We further predict that in the high‐temperature cubic phase, Pb and Sn compounds will mix for both and due to the entropy contribution to the Helmholtz free energy.

Dielectric studies of multiferroic orthochromites Ho0.9(RE)0.1CrO3 (where RE=Gd and Yb)

Dielectric studies have been made on two orthochromite systems, Ho0.9Gd0.1CrO3 and Ho0.9Yb0.1CrO3. In the known multiferroic system of HoCrO3, Ho is substituted by one lower and one higher atomic number rare earth element (Gd and Yb respectively). Solid state diffusion method has been used to synthesize these polycrystalline samples. X-ray diffraction patterns for both the samples show a distorted orthorhombic perovskite phase. Temperature and frequency dependent dielectric measurements on the Gd and Yb substituted samples show ferroelectric nature with ferroelectric to paraelectric (FE–PE) transitions occurring at Curie temperature (Tc)∼530(5)K and ∼490(5)K (at excitation frequency of 1kHz) respectively. The two studied systems are non-Debye relaxor ferroelectrics and the FE–PE transitions exhibit high diffusiveness.

X-ray Diffraction, Dielectric, and Raman Spectroscopy Studies of SrTiO3-Based Microwave Ceramics

xSrTiO3-(1 − x)Ca0.61Nd0.26TiO3 (SCNTx) and xSrTiO3-(1 − x)Na1/2La1/2TiO3 (SNLTx) ceramics were studied by x-ray diffraction and Raman spectroscopy in the composition range of 0.1 ≤ x ≤ 0.4. The x-ray patterns illustrated that the SCNTx (0.1 ≤ x ≤ 0.4) solid solutions had a single orthorhombic perovskite phase, while a single phase with pseudoorthorhombic structure was identified for the SNLTx (0.1 ≤ x ≤ 0.4) ceramics. In addition, the Lorentz fitting method was applied to separate the Raman spectra into several individual peaks. Meanwhile, the line shift and width of the main phonons are also discussed based on the Lorentz fitting method. Among these, some new peaks at about 470 cm−1/483 cm−1 and 442.31 cm−1/429.20 cm−1 appeared for the SCNTx and SNLTx samples with 0.3 ≤ x ≤ 0.4 due to A-site occupation by two or more types of cation with different electrovalence. Based on the resulting Q × f value and full-width at half-maximum of the A1g(O) stretch mode, it was found that propagation of microwave energy in the SCNTx samples showed stronger damping behavior; a smaller Q × f value was therefore expected with an increase in Sr content. Moreover, the τf value and tolerance factor (t) exhibited a proportional correlation because of increasing symmetry of the perovskite phase for the SNLTx (0.1 ≤ x ≤ 0.4) ceramics.

Effects of substituting Ca2+ on the structure and electrical properties of 0.6Y2O3–0.4YCr0.5Mn0.5O3 composite NTC ceramics

New high temperature negative temperature coefficient (NTC) thermistors based on the 0.6Y2O3–0.4Y1−x Ca x Cr0.5Mn0.5O3 (0 ≤ x ≤ 0.15) composite system have been prepared through the conventional solid-state reaction. The effects of Ca doping on the structure and electrical properties of 0.6Y2O3–0.4Y1−x Ca x Cr0.5Mn0.5O3 have been investigated. The major phases presented in the samples are Y2O3 phase and orthorhombic perovskite phase isomorphic to YCrO3. The resistance decreases with increasing temperature from 25 to 1000 °C, indicative of NTC characteristics. The resistance of NTC thermistors decreases with the increase of Ca content as a result of the enhancement of Cr4+ and Mn4+ concentration, which has been explained by using defect chemistry theory. The values of ρ 25, B 25−150 and B 700–1000 of 0.6Y2O3–0.4Y1−x Ca x Cr0.5Mn0.5O3 NTC thermistors are in the range of 2.73 × 104–3.86 × 105 Ω cm, 2952–3553, 5790–8391 K, respectively. These values can be tuned with the Ca content. These compounds could be used as potential candidates for high temperature thermistors applications.

Influence of Microstructure and Surface Activation of Dual‐Phase Membrane Ce0.8Gd0.2O2−δ–FeCo2O4 on Oxygen Permeation

Dual‐phase oxygen transport membranes are fast‐growing research interest for application in oxyfuel combustion process. One such potential candidate is CGO‐FCO (60 wt% Ce0.8Gd0.2O2−δ–40 wt% FeCo2O4) identified to provide good oxygen permeation flux with substantial stability in harsh atmosphere. Dense CGO‐FCO membranes of 1 mm thickness were fabricated by sintering dry pellets pressed from powders synthesized by one‐pot method (modified Pechini process) at 1200°C for 10 h. Microstructure analysis indicates presence of a third orthorhombic perovskite phase in the sintered composite. It was also identified that the spinel phase tends to form an oxygen deficient phase at the grain boundary of spinel and CGO phases. Surface exchange limitation of the membranes was overcome by La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) porous layer coating over the composite. The oxygen permeation flux of the CGO‐FCO screen printed with a porous layer of 10 μm thick LSCF is 0.11 mL/cm2 per minute at 850°C with argon as sweep and air as feed gas at the rates of 50 and 250 mL/min.

Nickel Doped Lanthanum Chromite Perovskite: A Novel Regenerable Anode Material for Solid Oxide Fuel Cells

A series of nickel doped lanthanum strontium chromite (La0.7Sr0.3Cr1-xNixO3-y, x=0.05-0.3) perovskite anodes for SOFCs was fabricated by glycine combustion method. The structural properties and electrochemical performances of the anode materials were investigated. It was found that the materials with various nickel dopant content showed an orthorhombic perovskite phase. However the formation of parasitic phase of NiO could also be detected for the material with nickel content >20%. Thermogravimetric analysis (TGA) measurement performed in 5% H2-N2 showed that the mobility of oxygen in the materials increased with the increase of Ni content. For La0.7Sr0.3Cr0.8Ni0.2 (LSCNi) sample, Scan Electron Microscope (SEM) images detected the in-situ growth of nano Ni particles with the average diameter of 20 nm anchoring on surface of the material after the exposure in reducing atmosphere. The material with exsolution of Ni nano particle displayed improved power density output and reduced the activation polarization resistance compared to pure La0.7Sr0.3CrO3-y (LSC). Figure 1

Nickel Doped Lanthanum Chromite Perovskite: A Novel Regenerable Anode Material for Solid Oxide Fuel Cells

A series of nickel doped lanthanum strontium chromite (La0.7Sr0.3Cr1-xNixO3-y, x=0.05-0.3) perovskite anodes for SOFCs was fabricated by glycine combustion method. The structural properties and electrochemical performances of the anode materials were investigated. It was found that the materials with various nickel dopant contents showed an orthorhombic perovskite phase. However the formation of parasitic phase of NiO could also be detected for the material with nickel content >20%. Thermogravimetric analysis (TGA) measurement performed in 5% H2-N2 showed that the mobility of oxygen in the materials increased with the increase of Ni content. For La0.7Sr0.3Cr0.8Ni0.2 (LSCNi) sample, Scan Electron Microscope (SEM) images detected the in-situ growth of nano Ni particles with the average diameter of 20 nm anchoring on surface of the material after the exposure in reducing atmosphere. The material with exsolution of Ni nano particle displayed improved power density output and reduced the activation polarization resistance compared to pure La0.7Sr0.3CrO3-y (LSC).

In-depth structure characterization and properties of (1−x)(Li0.05Na0.475K0.475)(Nb0.95Sb0.05)O3−xBiFeO3 lead-free piezoceramics

(1−x)(Li0.05Na0.475K0.475)(Nb0.95Sb0.05O3)−xBiFeO3 ceramics were prepared by the conventional sintering method. The microstructure, phases and their relative volume fractions were investigated in detail by using transmission electron microscopy and X-ray diffraction. Fullprof and Topas softwares were also used to refine the X-ray diffraction data to confirm the crystal structure. The refinement results show that for x ≤ 0.008, the ceramics consists of the orthorhombic and tetragonal perovskite phases, and the fraction of the orthorhombic phase decreases from 50.66 % for x = 0.0 to 40.62 % for x = 0.008. When x = 0.01, the ceramics has a mixed microstructure with three coexisting phases: the orthorhombic, tetragonal perovskite phases and tetragonal tungsten bronze-type structure phase, and the fraction of the tetragonal tungsten bronze-type structure phase is 6.72 %. The selected area electron diffraction data is also consistent with the space groups for all of the above phases. This system also exhibits good ferroelectric and piezoelectric properties for applications, for example, at x = 0.004, the ceramic samples have a piezoelectric constant (d 33) of 272 pC/N and remanent polarization (P r) of 20.6 μC/cm2.

Phase stability and transformations in the halide perovskiteCsSnI3

We employ the quasiharmonic approximation to study the temperature-dependent lattice dynamics of the four different phases of cesium tin iodide $({\mathrm{CsSnI}}_{3})$. Within this framework, we obtain the temperature dependence of a number of structural properties, including the cell volume, bulk modulus, and Gr\uneisen parameter. The Gibbs free energy of each phase is compared against the temperature-dependent Helmholtz energy obtained from the equilibrium structure within the harmonic approximation. We find that the black tetragonal perovskite phase is not dynamically stable up to at least 500 K, with the phonon dispersion displaying negative optic modes, which pass through all of the high-symmetry wave vectors in the Brillouin zone. The main contributions to the negative modes are found to be motions of the Cs atom inside the perovskite cage. The black cubic perovskite structure shows a zone-boundary instability, indicated by soft modes at the special $\mathbf{q}$ points $M$ and $R$. These modes are present in calculations at the equilibrium (0 K) lattice constant, while at finite temperature additional negative modes develop at the zone center, indicating a ferroelectric instability. The yellow crystal, composed of one-dimensional $({\mathrm{SnI}}_{6}){}_{n}$ double chains, has the same heat of formation as the orthorhombic perovskite phase at 0 K, but becomes less energetically favorable at higher temperatures, due to its higher free energy.

Microstructures and microwave dielectric properties of (1 − x)Sr0.2Na0.4Sm0.4TiO3–xLnAlO3 (Ln = Nd, Pr and Sm) ceramic systems

The microstructures and microwave dielectric properties of the (1 − x)Sr0.2Na0.4Sm0.4TiO3–xLnAlO3 samples (where Ln stands for Nd, Pr and Sm, x = 0.2–0.3) were studied. The XRD result showed that the (1 − x)Sr0.2Na0.4Sm0.4TiO3–xLnAlO3 (Ln = Nd, Pr and Sm) solid-solutions with single orthorhombic perovskite phase could be formed in the componential range of 0.2 ≤ x ≤ 0.3. With an increasing of Ln3+ content, the dielectric constant (e r ) decreased due to the smaller dielectric polarizability of LnAlO3 than that of Sr0.2Na0.4Sm0.4TiO3. With increasing x from 0.2 to 0.3, the quality factor (Q·f) firstly increased and then decreased for the specimens with PrAlO3, because the Q·f values were strongly depended on grain sizes. Moreover, either increasing the A-site bond valence or decreasing the B-site bond valence led to a decrease in the temperature coefficient of the resonant frequency (τ f). Typical values of e r ~ 52.7, Q·f ~ 9700 GHz (at 4.33 GHz) and τ f ~ 1.5 ppm/°C were obtained for the (1 − x)Sr0.2Na0.4Sm0.4TiO3–xSmAlO3 (x = 0.25) ceramic sintered at 1470 °C for 4 h.