Perovskite-type Solid Solutions Research Articles

Synthesis and Exploration of Barium Stannate-Zirconate BaSn1-xZrxO3 (0 ≤ X ≤ 1) Solid Solutions as Photocatalysts.

Employing ionic liquid-assisted microwave synthesis and moderate heat treatment allows for the preparation of otherwise difficult-to-obtain perovskite-type BaSn1-xZrxO3 solid solutions (0 ≤ x ≤ 1). The impact of substituting Sn for the crystal structure, crystallinity, morphology, and photocatalytic performance was investigated. The obtained materials are characterized by X-ray diffraction, scanning electron microscopy, Brunauer-Emmett-Teller (BET) surface area analysis, X-ray photoelectron spectroscopy, UV-Vis diffuse reflectance spectroscopy, photoluminescence spectroscopy, and Raman and IR spectroscopy. SEM images show that the morphology of the samples varies from rods for x = 0, 0.2 to spherical for x = 0.5, 0.8, 1. Upon Zr for Sn substitution, the band gap changes from 3.1 to 5.0 eV as the valence and conduction bands move to lower and higher energies. The photocatalytic activities of the BaSn1-xZrxO3 samples in the hydroxylation of terephthalic acid (TA) follow the order BaSn0.5Zr0.5O3> BaSn0.8Zr0.2O3> BaSnO3> BaSn0.2Zr0.8O3> BaZrO3. The superior photocatalytic activity of BaSn0.5Zr0.5O3 can be attributed to the synergistically favorable combination of a suitable band structure, band gap size, and increased surface area-to-volume ratio, resulting in a diminished crystalline particle size unattainable from samples prepared via traditional synthetic routes or without ionic liquid.

Photoluminescence properties of Ba0.7Sr0.3TiO3:Sm3+ modified K0.5Na0.5NbO3 perovskite oxide ceramics

Ba0.7Sr0.3TiO3:Sm3+ modified KxNa(1-x)NbO3 ceramics with perovskite-type structure were synthesized via solid state sintering method. Sm3+ ions doping was designed for substituting both A and B sites in the ABO3 structure, Sm3+ doped Ba0.7Sr0.3TiO3 (Ba0.7Sr0.3TiO3:Sm3+) oxide precursor powders with the chemical formula of Ba0.7Sr0.3-xSmx(Ti1-xSmx)O3 (x=0.005 ， 0.015 ， 0.025) were synthesized. Combined Ba0.7Sr0.3TiO3:Sm3+ with K0.5Na0.5NbO3, the perovskite-type solid solution composite ceramics were fabricated via solid phase sintering method. X-Ray diffraction was used for investigating the phase structure of the precursor powders and luminescent composite ceramics. The photoluminescence properties of the Sm3+ ions in the Ba0.7Sr0.3TiO3-K0.5Na0.5NbO3 composite ceramic materials were systematically investigated by exploring the effects of composition of the composites, excitation wavelength and temperature on photoluminescence.

Features of coexistence of tetragonal and orthorhombic phases in lead-free ferroelectric solid solutions

A model of a heterophase sample with interlayers is proposed to describe coexistence of tetragonal and orthorhombic phases in lead-free perovskite-type ferroelectric solid solutions. Versions of phase coexistence are analyzed at variations of unit-cell parameters of (Ba, Ca)(Ti, Zr)[Formula: see text] and (K, Na)(Nb, Sb)[Formula: see text]-(Ba, Ca)[Formula: see text] with compositions near morphotropic phase boundaries. Large regions of the tetragonal and orthorhombic phases are split into [Formula: see text] and [Formula: see text] domains, respectively. The interlayer of the orthorhombic phase is either single-domain or split into [Formula: see text] domains. A complete stress relief can be achieved at an elastic matching of the polydomain/single-domain or polydomain/polydomain phases. It is shown that different phase contents in ([Formula: see text])[Formula: see text]([Formula: see text])[Formula: see text] powder and ceramic are caused by different non-[Formula: see text] domain structures in the phases. The interlayer of the orthorhombic phase plays an important role in forming the phase content in solid solutions. Agreement is shown when comparing the evaluated volume fractions of the orthorhombic phase to experimental data.

Perovskite-Type Solid Solution Nano-Electrocatalysts Enable Simultaneously Enhanced Activity and Stability for Oxygen Evolution.

A trade-off between catalytic activity and structural stability generally exists in oxygen evolution electrocatalysis, especially in acidic environment. This dilemma limits the development of higher-performance electrocatalysts that are required by next-generation electrochemical technologies. Here it is demonstrated that the inverse catalytic activity-structural stability relation can be broken by alloying catalytically inert strontium zirconate with the other catalytically active perovskite, strontium iridate. This strategy results in an alloyed perovskite electrocatalyst with simultaneously improved iridium mass activity and structural stability, by about five times, for the oxygen evolution reaction under acidic conditions. The experimental and theoretical results suggest that the alloying strategy generates multiple positive effects, mainly including the reduction of catalyst size, the decrease of catalyst covalency, and the weakening of surface oxygen-binding ability. The synergistic optimization of bulk and surface properties, as a result, enhances the intrinsic activity and availability of surface iridium sites, whilst significantly inhibiting the surface cation corrosion during electrocatalysis.

Tuning the temperature-induced local-dipole coupling in (1−x)Na0.5Bi0.5TiO3-xBaTiO3 via electric field

In situ temperature-dependent Raman-scattering experiments under an external dc electric field E have been performed on (1−x)Na0.5Bi0.5TiO3-xBaTiO3 single crystals with x ranging from 0.013 to 0.074 in order to gain further insights into the atomistic mechanism of polar coupling in lead-free perovskite-type (ABO3) ferroelectric solid solutions near the morphotropic phase boundary (MPB). The polarized Raman spectra collected between 770 and 100 K under an E applied along the pseudocubic [100] direction were analyzed in terms of hard-mode spectroscopy. The results reveal enhanced coupling between the polar displacements of the A-site Bi3+ and B-site Ti4+ cations for x=0.048∼xMPB when a moderate E[100] field is applied, a local-scale phenomenon that might be responsible for the known drift of the MPB under external stimuli. In addition, for all studied compounds, the characteristic temperatures TA−A′ and TA−A′′, preceding the macroscopic Tm and Td and related to mesoscopic-scale antiferroelectric and ferroelectric coupling processes within the A-site-cation subsystem in a zero field, merge into one even under a weak electric field, suggesting that the structural state between the paraelectric and ferroelectric zones in the x-T diagram is weak ferrielectric.

Study on phase structures and compositions, microstructures, and dielectric characteristics of (1-x)NdGaO3-xBi0.5Na0.5TiO3 microwave ceramic systems

(1–x)NdGaO3-xBi0.5Na0.5TiO3 [(1–x)NdGaO3-xBNT, 0.05 ≤ x ≤ 0.7)] ceramic systems were fabricated using a conventional solid-state reaction, and their phase structures, microstructures, and microwave dielectric characteristics were systematically investigated. The XRD patterns results showed an orthorhombic perovskite structure as the main phase with a Pbnm space group at x = 0.05. In a range of x = 0.1–0.3, the main Nd3Ga5O12 cubic structure phases (Ia-3d space group) had been formed due to the increase in the cation vacancies resulting from the Na and Bi ion volatilization at the higher densification sintering temperatures (1400–1450 °C). As (Na0.5Bi0.5)2+ ions increased and the sintering temperatures decreased, the orthorhombic perovskite-type Pnma space group solid solutions (the main phases) were detected at x = 0.4 and 0.5, accompanied with a certain amount of second phase Bi2O3 in the samples at x = 0.6 and 0.7. The results of Raman spectroscopy analysis, EDS data analysis, and surface morphologies observations were basically in keeping well with the XRD analysis results, wherein the Raman-active modes also implied that the crystal structure of the main phase actually had a tendency to change the perovskite structure when x = 0.3. The εr value increased gradually as the x value increased from 0.05 to 0.5 because of the increase in the ionic polarizability, and increased slowly at x = 0.6, then decreased slightly as the x value further increased to 0.7 due to the formation of the second phase. The Q × f values of the (1-x)NdGaO3-xBNT (x = 0.05–0.7) ceramic systems were strongly influenced by the densification, lattice defects, and phase composition and content. The τf values could be well predicted by replacing Na, Bi and Ti ions with suitable substitutions for these ceramic systems. As a result, the new temperature-stable ceramics with optimal dielectric properties of εr ~43.1, Q × f ~6700 GHz (at 5.85 GHz), and τf ~ −24.5 ppm/°C and εr ~ 44.5, Q × f ~ 5600 GHz (6.12 GHz), and τf ~ +2.4 ppm/°C were obtained in the (1-x)NdGaO3-xBNT composite series at x = 0.5 and x = 0.6 sintered at 1320 °C and 1250 °C for 4 h, respectively.

High energy storage performance and fast discharging speed in dense 0.7Bi0.5K0.5TiO3-0.3SrTiO3 ceramics via a novel rolling technology

In this study, a ceramic with a 0.7Bi0.5K0.5TiO3-0.3SrTiO3 composition was designed to enhance its energy storage performance via rolling technology. Temperature had a great influence on microstructural refinement and energy storage density. A high recoverable energy storage density of 2.31 J/cm3 and efficiency of 77.7% were obtained under an optimal sintering temperature of 1175 °C. Specifically, a pulsed circuit indicated that stored energy was quickly released at a sub-microsecond scale of 0.26 μs. This study showed that Bi0.5K0.5TiO3-based ceramics, as new lead-free bismuth-based perovskite-type solid-solutions are promising candidates in pulsed-power applications.

Effects of local distortion on the electrical properties of lead free perovskite-type electro-ceramics Ba1-xCaxTi0.9Zr0.1O3

The electro-ceramic industry has focused their attention on replacing lead-based materials due to their toxic effects and unfavourable environment impact. Barium titanate doped with calcium and zirconium denoted in this work as BCZT is a well-known perovskite-type solid solution. In particular, Ba1-xCaxTi0.9Zr0.1O3 (where x = 0, 0.1 and 0.15) compositions are located near the so called morphotropic phase boundary (MPB): coexistence of ferroelectric phases. This work shows the relationship between the crystal and electronic structure with the dielectric and piezo-ferroelectric properties. The high-resolution X-ray diffraction (HR-XRD) results suggest the coexistence of tetragonal and rhombohedral phases over the obtained compositions. The dielectric analysis indicates a relaxor behaviour with a Curie temperature in a range of 100-120°C. Piezoelectric and ferroelectric evaluation complement the electrical characterization for these compositions. Micro–X-ray absorption near edge spectroscopy (μ-XANES) was performed to monitor possible changes of electronic structure profile due to the local distortions as Ca2+ increases.

Near-infrared persistent luminescence in Mn4+ doped perovskite type solid solutions

Persistent luminescent phosphors with near-infrared emission have attracted attention in recent years for their promising bio-imaging applications. In the development of persistent materials in the near-infrared wavelengths, Mn4+ is regarded as a promising candidate owing to the 2Eg → 4A2g emission in the deep-red or near-infrared range. In this work, a series of Mn4+ doped perovskite type LaAl1-xGaxO3 and La1-xGdxAlO3 solid solutions with different compositions were successfully prepared using a high temperature solid state reaction method. Mn4+ occupied octahedral positions to substitute Al3+ or Ga3+ in these solid solutions and the 2Eg → 4A2g emission of Mn4+ was tailored by the different local environments of the hosts. Tunable NIR persistent luminescence was achieved by the crystal field control and composition modification. The trap levels of these solid solutions were investigated using thermoluminescence measurements. This kind of perovskite type-based solid solution with tunable near-infrared emission is highly desirable for medical imaging applications.

Electrical and optical properties of lead-free 0.15(K0.5Bi0.5TiO3)–0.85(NaNbO3) solid solution

Polycrystalline lead free 0.15(K0.5Bi0.5TiO3)–0.85(NaNbO3) ceramic is synthesized using conventional solid state reaction technique. Structural, dielectric, optical and impedance properties of the sample are investigated. X-ray diffraction (XRD) study reveals K0.5B0.5TiO3 (KBT) diffusing into the NaNbO3 (NN) lattices to form a new perovskite-type solid solution with orthorhombic structure (space group Pmc2 1 ) at room temperature. Addition of small amount of KBT transforms NN ceramic from anti-ferroelectric to ferroelectric material. The XRD data has been refined using Rietveld refinement technique. FTIR spectra reflect an appreciable change in its vibrational phonon modes of the sample. The optical band gap is estimated to be 3.02 eV from the diffused absorbance spectra, which is useful in photo catalytic applications. Different vibrational modes in the frequency range of 130–900 cm−1 is observed from the Raman spectrum. FESEM micrograph reveals the homogeneous grains and well-defined grain boundaries with some few pores. Dielectric and complex impedance spectroscopic studies are carried out in a wide range of frequency (i.e., 103–106 Hz) and temperature (30–475 °C). The presence of ferroelectric properties is confirmed from P–E loop. A strong correlation between its microstructure and electrical parameters is established from the study of the electrical properties of the material. The ac conductivity spectrum obeys Jonscher’s power law. Negative temperature coefficient of resistance behavior of the material is inferred from temperature dependence of dc conductivity.

The effects of PbZn1/3Nb2/3O3-doping on structural, thermal, optical, dielectric, and ferroelectric properties of BaTiO3 ceramics

Low-lead (1-x)BT-xPZN (x = 0, 0.025, 0.05, 0.075, 0.10, 0.125, and 0.15) ceramics were successfully synthesized by the spark-plasma-sintering method for the first time. Their phase transition behavior as well as structural, thermal, optical, and electrical properties was investigated. These materials exhibit the structure of perovskite-type solid solutions and undergo a sequence of phase transitions, typical of pure BaTiO3 (BT). The dielectric test results revealed that with the increase in the PbZn1/3Nb2/3O3 (PZN) content, the frequency dispersion of electric permittivity increases, whilst the dielectric/ferroelectric properties tend to deteriorate, which is characteristic of relaxor-type behavior. Therefore, it is reasonable to suppose that these ceramics progressively lack long-range ordering. These effects are due to the competition between lone-pair electrons' induced changes in the A-O band upon Pb2+ addition and ionic size differences. In general, the transition temperatures observed by dielectric analyses are in good agreement with those obtained from X-ray diffraction and differential scanning calorimetry measurements. The BT-PZN system may help to understand why relaxor behavior appears in perovskite-based materials. It appears that these materials can become a good starting point for the development of new low-lead electronic ceramics.

Phase formation in the BaCO3–PbO–Fe2O3–Nb2O5 system

Features of the formation of lead-ferroniobate compounds in the xBaCO3–(1 – x)PbO–Fe2O3–Nb2O5 system by solid-phase synthesis are investigated. For perovskite-type lead-ferroniobate solid solution, a single-phase concentration region is revealed at 1233 K. The crystalline structures of the synthesized compounds are refined using Rietveld analysis and the Pm3m and R3m space groups. Ceramic samples of lead ferroniobate are studied by scanning electron microscopy.

The effect of iridium oxidation state on the electronic properties of perovskite-type solid solutions: Ba2–xLaxInIrO6 and BaLaIn1–yCayIrO6

Two novel solid solution series, Ba2-xLaxInIrO6 (x=0–1.0) and BaLaIn1-yCayIrO6 (y=0–1.0), were prepared and several changes in structure, moment and charge transport were observed. The Ba2-xLaxInIrO6 series exhibits a transition from a 6M polytype to an orthorhombic perovskite structure with increased La content whereas the BaLaIn1-yCayIrO6 series transitioned from a disordered, orthorhombic perovskite to an ordered, cubic perovskite with increased Ca content. Seebeck measurements for both systems showed that Ir(IV)-rich compounds tended to have a n-type conduction mechanism while Ir(V)-rich compounds tended to be p-type. Both systems were found to be semiconducting and the magnitude of the resistivity is dependent on crystal structure and Ir environment. Magnetic measurements show that the μeff values for both systems are significantly less than predicted for Ir(IV) (1.73 μB) and greater than predicted for Ir(V) (0 μB). These results are compared to other iridate compound families.

Improved transverse piezoelectric properties in {110}-oriented B-site acceptor doped PLZT (8/65/35) thin films

ABSTRACTSuperior piezoelectric properties of lead-based perovskite type solid solution systems such as PLZT, having compositions near morphotropic phase boundary (MPB) make them ideal candidates for MEMS. The dielectric and piezoelectric characteristics in such perovskite based thin films are related to their structure and texture. In this study, we report the influence of aliovalent B-site acceptor dopants (Fe3+, Cu2+ and Mn3+) on the structure, dielectric and piezoelectric properties of {110}- preferentially oriented PLZT (8/65/35) thin films. Thin films having a thickness of 2.0 µm were prepared on silicon substrates (111) Pt/Ti/SiO2/Si by Sol-gel spin coating technique. The preferential crystallographic orientation and crystalline phase formation in the thin films were analysed by X-ray diffraction and Raman spectroscopy respectively. The improved transverse piezoelectric coefficient, e31,f and electric field induced bipolar strain characteristics of the acceptor doped PLZT films have been correlated with their crystal structure. Mechanism for higher bipolar strain in Cu2+ and Mn3+ doped PLZT films have also been studied and are reported.

Molecular Dynamics Simulations of Chemically Disordered Ferroelectric (Ba,Sr)TiO3 with a Semi-Empirical Effective Hamiltonian

We present a semi-empirical effective Hamiltonian to capture effects of disorder associated with Ba and Sr cations occupying $A$ sites in (Ba$_{x}$Sr$_{1-x}$)TiO$_3$ on its ferroelectric phase transition. Averaging between the parameters of first-principles effective Hamiltonians of end members BaTiO$_3$ and SrTiO$_3$, we include a term with an empirical parameter to capture the local polarization and strains arising from the difference between ionic radii of Ba and Sr. Using mixed-space molecular dynamics of the effective Hamiltonian, we determine $T$-dependent ferroelectric phase transitions in (Ba$_{x}$Sr$_{1-x}$)TiO$_3$ which are in good agreement with experiment. Our scheme of determination of semi-empirical parameters in effective Hamiltonian should be applicable to other perovskite-type ferroelectric solid solutions.

Williamson–Hall analysis and the dielectric behavior of complex perovskites (BaM0.9M′0.1)0.984O3 (M=Ti, Zr; M′=Nb, Ta)

The long range average structure and local distortions of perovskite type solid solutions (BaTi0.9M′0.1)0.984O3 and (BaZr0.9M′0.1)0.984O3 (M′=Nb, Ta) were examined by high-resolution synchrotron X-ray diffraction. A Rietveld refinement indicated that all four solid solutions had simple cubic symmetry, where the lattice volume varied according to the size of the cationic constituents. As revealed by Williamson–Hall analysis and scanning electron microscopy, both (BaTi0.9M′0.1)0.984O3 had denser and enlarged grains than the parental BaTiO3, and had anisotropic microstrain that are indicative of the non-periodic atomic displacements along the [100] directions of the cubic cell. (BaTi0.9Nb0.1)0.984O3 and (BaTi0.9Ta0.1)0.984O3 exhibited relaxor-like dielectric behavior with Curie temperatures of 230K and 195K, respectively. On the other hand, (BaZr0.9Nb0.1)0.984O3 and (BaZr0.9Ta0.1)0.984O3 showed almost unchanged dielectric behavior compared to that of BaZrO3.

Interrelationship between Interphase Boundaries and Phase Contents near the Critical Compositions of Lead-Free Ferroelectric (Na0.5Bi0.5)TiO3−BaTiO3

Heterophase structures in lead-free perovskite-type ferroelectric solid solutions of (1 − z)(Na0.5Bi0.5)TiO3 − zBaTiO3 are analysed for a few critical compositions near the morphotropic phase boundary (z = 0.05−0.07). Examples of the phase coexistence and elastic matching of the phases from different symmetry groups are considered to find optimum volume fractions of specific domain types and coexisting phases at the complete stress relief in two-phase samples. Some interrelations between these volume fractions are described using variants of the domain arrangement at changes in the composition and unit-cell parameters. The evaluated room-temperature volume fractions of the ferroelectric monoclinic (Cm symmetry) and tetragonal (P4mm symmetry) phases near the morphotropic phase boundary are in agreement with experimental data.

Reconsideration of the morphotropic phase boundary - the order of the ferroelectric phase transition -

The morphtropic phase boundary existing in a perovskite-type solid solution like Pb(Zr,Ti)O3 (PZT) is reconsidered in relation to the order of the ferroelectric phase transition. For the secondorder transition from the paraelectric cubic phase, at the triple point S where the cubic, tetragonal and rhombohedral phases meet, the free energy is isotropic in the order parameter space, and a vertical boundary guarantees dielectrically excellent properties, while for the first-order transition, at the triple point F, the free energy is usually anisotropic, and even a vertical boundary does not necessarily guarantee the best properties.

Magnetic properties of solid solutions between BiCrO3 and BiGaO3 with perovskite structures

Magnetic properties of BiCr1−xGaxO3 perovskite-type solid solutions are reported, and a magnetic phase diagram is established. As-synthesized BiCrO3 and BiCr0.9Ga0.1O3 crystallize in a monoclinic (m) C2/c structure. The Néel temperature (TN) decreases from 111 K in BiCrO3 to 98 K in BiCr0.9Ga0.1O3, and spin-reorientation transition temperature increases from 72 K in BiCrO3 to 83 K in BiCr0.9Ga0.1O3. o-BiCr0.9Ga0.1O3 with a PbZrO3-type orthorhombic structure is obtained by heating m-BiCr0.9Ga0.1O3 up to 573 K in air; it shows similar magnetic properties with those of m-BiCr0.9Ga0.1O3. TN of BiCr0.8Ga0.2O3 is 81 K, and TN of BiCr0.7Ga0.3O3 is 63 K. Samples with x = 0.4, 0.5, 0.6 and 0.7 crystallize in a polar R3c structure. Long-range antiferromagnetic order with weak ferromagnetism is observed below TN = 56 K in BiCr0.6Ga0.4O3, TN = 36 K in BiCr0.5Ga0.5O3 and TN = 18 K in BiCr0.4Ga0.6O3. BiCr0.3Ga0.7O3 shows a paramagnetic behaviour because the Cr concentration is below the percolation threshold of 31%.

Quantitative Microanalysis of (1-x)Pb(Mg(1/3)Nb(2/3))O3×xPbTiO3 (PMNT) Ferroelectric Ceramics.

Optimized quantitative electron-probe microanalysis was applied for compositional characterization of a ferroelectric ceramic single crystal that was made from the complex perovskite-type solid-solution (1-x)Pb(Mg(1/3)Nb(2/3))O3×xPbTiO3 (PMNT). Cation concentrations were determined with high accuracy and ultimate relative experimental uncertainty of ≤±1%, showing that the average chemical composition of the crystal corresponds to Pb(Mg(1/3)Nb(2/3))(0.67)Ti(0.33)O3 (i.e., x=0.33), which is close to the morphotropic phase boundary composition. Over the PMNT single crystal slight compositional heterogeneity was measured for concentrations of the perovskite B-site cations Ti4+, Mg2+, and Nb5+, with variations up to ±2.3%, whereas the Pb concentration remained uniform within a variation below ±0.5%.