Perovskite-type Solid Solutions Research Articles

PbMg1/3Nb2/3O3-doping effects on structural, thermal, Raman, dielectric and ferroelectric properties of BaTiO3 ceramics

Low-lead content (1−x)BT–xPMN (x=0, 0.025, 0.05, 0.075, 0.10 and 0.15) ceramics were prepared by a two-step conventional mixed-oxide method. The crystal structure, phase transitions behavior, thermal, Raman and electrical properties of these ceramics were investigated for the first time. The compositions show formation of perovskite-type solid solutions and undergo a sequence of phase transitions characteristic of pure BT (except for samples with x=0.075 and x=0.10 in which a direct tetragonal–rhombohedral phase transition, and x=0.15 in which only cubic–rhombohedral phase transition, was observed). Dielectric studies revealed that, with a rise of PMN content, the dielectric behaviors of the obtained ceramics changed from that of normal ferroelectrics to relaxor-like ones. The transition temperatures and the maximum electric permittivity decrease with increasing PMN content in the system. In general, the transition temperatures observed by means of dielectric studies are in good agreement with those obtained from XRD and DSC measurements. The possible origin of the observed effects was discussed. We suggest that the presented materials can be a good starting point for the development of new low-lead electronic ceramics.

2–2 composites based on [011]-poled relaxor-ferroelectric single crystals: analysis of the piezoelectric anisotropy and squared figures of merit for energy harvesting applications

In this paper we explore the effect of the orientation of the main crystallographic axes in relaxor-ferroelectric single crystals (SCs) on the piezoelectric anisotropy and squared figures of merit of 2–2 parallel-connected SC/auxetic polymer composites. The single-crystal component for the composite is chosen from the perovskite-type solid solutions with compositions near the morphotropic phase boundary and poled along the perovskite unit-cell [011] direction (mm 2 symmetry of domain-engineered SCs). The orientation of the main crystallographic axes in the single-crystal component is observed to strongly influence the piezoelectric coefficients $$d_{3j}^{*}$$ , squared figures of merit $$d_{3j}^{*}$$ $$g_{3j}^{*}$$ , electromechanical coupling factors $$k_{3j}^{*}$$ , and hydrostatic analogs of these parameters of the 2–2 composite. Inequalities $$| {d_{33}^{*} /d_{3f}^{*} } | > 5$$ and $$| {k_{33}^{*} /k_{3f}^{*} } | > 5$$ (f = 1 and 2) are achieved at specific orientations of the main crystallographic axes due to the significant anisotropy of the elastic and piezoelectric properties of the single-crystal component. The use of an auxetic polyethylene (a polymer component with a negative Poisson’s ratio) leads to a significant increase in the hydrostatic parameters. Particular advantages of such composites over conventional ceramic/polymer composites are taken into account for transducer, hydroacoustic, energy harvesting, and other applications.

Domain type-phase content interrelations in perovskite-type ferroelectric solid solutions

Results from studying heterophase states and phase contents are generalized for perovskite-type ferroelectric solid solutions with compositions near the morphotropic phase boundary. The volume contents of phases are predicted with allowance for various non-180° domain types upon complete relief of internal mechanical stresses in heterophase regions.

Effect of a tetragonal phase on heterophase states in perovskite-type ferroelectric solid solutions

Results on the role of the ferroelectric tetragonal (P4mm) phase in an elastic matching and phase coexistence are discussed for perovskite-type solid solutions (1−t)BiFeO3–tPbTiO3, (1−z)Pb(ZrwTi1−w)O3–zPb(Zn1/3Nb2/3)O3 and (1−r)(Na1/2Bi1/2)TiO3–rPbTiO3 near morphotropic phase boundaries. An important feature is a combination of single- and polydomain regions of the tetragonal phase that coexists with the adjacent ferroelectric phase, either monoclinic or rhombohedral, at the complete stress relief in a heterophase sample. A dependence of the volume fraction of the tetragonal phase on the composition and domain types is found for various heterophase states in the aforementioned systems. The remarkable role of the tetragonal phase and its unit-cell parameters behaviour is discussed. Some correlations between changes in unit-cell parameters of the tetragonal phase and its volume fraction are revealed. Agreement between predicted and known experimental data on the phase contents in the studied ferroelectric solid-solution systems is stated.

Charge-Discharge Properties of PLZT x/90/10 Ceramics

This paper presents the results of investigations of the ceramic samples of perovskite type solid solution (Pb1-xLax)(Zr1-yTiy)O3 (PLZT—with x = 0.02, 0.03, 0.06 and 0.10, y = 0.9). Ceramic samples have been obtained from oxides using classical ceramic technology. The main aim of this paper is to compare the energy storage densities calculated from the P-E loops (at frequency of 1Hz) obtained as a result of integrating the area enclosed by E-P curve for tree types of ceramics—ferroelectric (PLZT with x = 0.02), slim-loop antiferroelectric (PLZT with x = 0.6, 0.10) and normal antiferroelectric with double loops (PLZT with x = 0.03).

First principles calculations of (Ba,Sr)(Co,Fe)O3 − δ structural stability

First principles total-energy calculations of an ideal BSCF perovskite-type solid solution, the crystal containing basic point defects, and a set of relevant solid–solid solutions are presented. Our DFT modeling of defects (Frenkel, Schottky and cation exchange) and disordering in the BSCF perovskites reveals that the material tends to decompose at relatively low temperatures into a mixture of new perovskite and oxide phases. These new phases are likely to appear at grain boundaries and surface interfaces. This instability is predicted to negate advantages of fast oxygen transport chemistry and impede the applicability of BSCF-based SOFC and ceramic permeation membranes. We discuss possible mechanisms and origins of defect-induced (in)stability in the context of available experiments. This research explains the observed SOFC performance reduction, the significant scattering in the reported degree of oxygen nonstoichiometry, and provides insights on enhancing mass transport and energy conversion in SOFC and oxygen separation ceramic membranes.

The formation of the complex manganites LnSr2Mn2O7 (Ln = La, Nd, Gd)

The process of formation of the Ruddlesden–Popper phases LnSr2Mn2O7 (Ln=La, Nd, Gd) was investigated by means of X-ray diffraction, thermal analysis and microprobe analysis. Two parallel pathways were found for the reaction. The first one includes the formation of the intermediate K2NiF4-type compound by interaction of Sr7Mn4O15 and perovskite-type solid solution (Ln,Sr)MnO3, while in the second one the K2NiF4-type intermediate is formed during the reaction of the same perovskite-type solid solution with the corresponding rare earth oxide. This result gives an explanation for the formation of two phases with slightly different cationic compositions. The kinetics of the reaction was investigated for both mechanisms resulting in determination of their relative contribution to the final composition. Pure NdSr2Mn2O7 was obtained using a step-by-step process according to the first mechanism, and the magnetic properties of this phase were investigated.

Heterophase States in Ferroelectric Solid Solutions: Examples of (1 – x)Pb(Fe1/2Nb1/2)O3 – xPbTiO3 and (Bi1−x Pb x )FeO3

The paper reports results on the phase coexistence in the perovskite-type ferroelectric solid solutions near the morphotropic phase boundary. Diagrams that describe features of the phase coexistence are put forward to interpret experimental data on various heterophase states in solid solutions of (1 – x)Pb(Fe1/2Nb1/2)O3 – xPbTiO3 and (Bi1−x Pb x )FeO3. The molar-concentration dependence of the volume fraction of the morphotropic phase is determined using experimental data on the unit-cell parameters of (1 – x)Pb(Fe1/2Nb1/2)O3 – xPbTiO3 (x = 0.05 – 0.08). The role of elastic matching of the phases and possibilities of the complete stress relief in wide temperature ranges are discussed.

Local structural phenomena in pure and Ru-doped0.9PbZn1/3Nb2/3O3−0.1PbTiO3near the morphotropic phase boundary as revealed by Raman spectroscopy

The development of polar order in perovskite-type (ABO${}_{3}$) solid solutions of relaxors and normal ferroelectrics is studied on the basis of the temperature dependence of polarized Raman spectra of pure and Ru-doped 0.9PbZn${}_{1/3}$Nb${}_{2/3}$O${}_{3}$-0.1PbTiO${}_{3}$ (PZN-0.1PT) single crystals as well as complementary x-ray diffraction analysis. It is shown that the Raman peaks related to Pb-localized vibrations existing solely in a double-perovskite structure (prototype symmetry $\mathit{Fm}\overline{3}m$) are highly sensitive to the nucleation and development of polar atomic arrangements. The doublet near 50 cm${}^{\ensuremath{-}1}$ observed in the high-temperature $\mathrm{Z\ifmmode \bar{}\else \={}\fi{}}(\mathit{XY})Z$ spectra of PZN-$x$PT ($x$ $=$ 0--0.1) is attributed to two distinct cubic states of Pb ions in regions with a local chemical B-site order of the type $\mathrm{Pb}({\mathrm{B}}_{2/3}^{2+}{\mathrm{B}}_{1/3}^{5+}){}_{0.5}{{\mathrm{B}}_{0.5}}^{5+}{\mathrm{O}}_{3}$: Pb1 ions surrounded mainly by Nb${}^{5+}$ and Pb2 ions surrounded by both Zn${}^{2+}$ and Nb${}^{5+}$. The singlet in the high-temperature $\mathrm{Z\ifmmode \bar{}\else \={}\fi{}}(\mathit{XY})Z$ spectra is assigned to off-centered Pb2 ions. The Raman spectra of PZN-0.1PT indicate that off-centered Pb2 ions induce coherent polar shifts of ferroelectrically active B cations, which in turn facilitates the off-centering of Pb1 ions. A low degree of B-site doping with mixed-valence elements like Ru can substantially influence the development of ferroelectric order in PZN-$x$PT solid solutions due to the different preferred types of local octahedral distortion associated with the different valence states of the doping cations. The incorporation of Ru into the structure of PZN-0.1PT slightly decreases the Burns temperature and shifts the tetragonal-to-monoclinic phase transition to lower temperatures, thus favoring the tetragonal state in a wider temperature range as compared to the undoped compound. An assumption is made that the nanoscale polar order in Pb-based B-site complex perovskite-type relaxors might be of ferrielectric type rather than of ferroelectric type.

Hydrothermal Synthesis and Characterization of (Na0.8K0.2)0.5Bi0.5TiO3 Perovskite-Type Oxides with Cubic Morghology

The (Na0.8K0.2)0.5Bi0.5TiO3 perovskite-type solid solution was prepared under mild condition at 160°C using Ti(OC4H9)4, Bi(NO3)3•5H2O as Bi and Ti sources by a mechanical hydrothermal method. It is suggested that mineralizer plays an important role in facilitating the crystallization of obtained products and promoting the formation of perovskite phase. The crystallized products were characterized by means of XRD, SEM and DSC-TG. The results show that the well-developed crystallite with a pure pervoskite structure has been formed. The powders with regular cubic morphology exhibit low agglomeration and narrow particles size distribution in the range of 3~6μm.

Piezoelectric Behavior Based on Mixing-Doped in Lead Zirconate Titanate Ceramics and Application

In this investigation, we extend our previous works to improve piezoelectric properties of Pb(Zr,Ti)O3 ceramics. Modified lead zirconate titanate (PZT) piezoceramics with a composition Zr/Ti=53/47 containing a trace of mixing dopants were prepared by conventional ceramic technology sintering powder compacts. Replacement of (Zr, Ti)+4 by Nb+5, Pb+2 by Sb+3 and Mn+4 in PZT perovskite type solid solutions was accomplished by the creation of cation and anion vacancies. Modified ceramics were explored as a function of firing temperature to acquire exceedingly good piezoelectric characterizations. From the analysis results, calcined at 850°C for 2 h, and then sintered at 1280°C for 2 h, PZT piezoceramic showed the larger dielectric constant er 2013, mechanical quality factor Qm 120 and maximum electromechanical coupling factor kp 0.67. Besides, the bulk ceramic grains distribution were found to be uniform. Furthermore, the sample was found to possess piezoelectric properties, the resonance frequency being about 200 KHz suitable for acoustic sensor.

Ionic Conduction and Fuel Cell Performance of Ba0.98Ce0.8Tm0.2O3−α Ceramic

The perovskite-type oxide solid solution Ba0.98Ce0.8Tm0.2O3−α was prepared by high temperature solid-state reaction and its single phase character was confirmed by X-ray diffraction. The conduction property of the sample was investigated by alternating current impedance spectroscopy and gas concentration cell methods under different gases atmospheres in the temperature range of 500–900°C. The performance of the hydrogen-air fuel cell using the sample as solid electrolyte was measured. In wet hydrogen, the sample is a pure protonic conductor with the protonic transport number of 1 in the range of 500–600 °C, a mixed conductor of proton and electron with the protonic transport number of 0.945-0.933 above 600 °C. In wet air, the sample is a mixed conductor of proton, oxide ion, and electronic hole. The protonic transport numbers are 0.010–0.021, and the oxide ionic transport numbers are 0.471-0.382. In hydrogen-air fuel cell, the sample is a mixed conductor of proton, oxide ion and electron, the ionic transport numbers are 0.942-0.885. The fuel cell using Ba0.98Ce0.8Tm0.2O3−α as solid electrolyte can work stably. At 900 °C, the maximum power output density is 110.2 mW/cm2, which is higher than that of our previous cell using BaxCe0.8RE0.2O3−α (x≤1, RE=Y, Eu, Ho) as solid electrolyte.

Oxide Ion Conduction in the Perovskite-type LaYO3 Doped with ZrO2

In order to find a new type of oxide ion conductor, the electrical conduction was measured in the substituted perovskite-type oxides. In the present case, LaYO3 was used as a based material with an orthorhombic and comparatively large unit cell, and a novel substitution method was introduced to intend to increase the concentration of oxide ions, e.g., LaY1−xZrxO3+x/2. As a result, the LaYO3-based perovskite-type solid solution was found to be formed, where the enhanced oxide ion conduction was observed as compared with that of the based material. A typical sample was LaY0.95Zr0.05O3.025, the ionic conduction of which was 1.2×10−2 S cm−1 at 1000°C. Another substitution method of La1−xZrxYO3+x/2 resulted in the analogous result. Considering these results and the further structural and density measurements, the charge carriers in these phases were expected to be due to interstitial oxide ions.

Ferroelectric and piezoelectric properties of new NaNbO3–Bi0.5K0.5TiO3 lead-free ceramics

New lead-free ceramics (1–x)NaNbO3–xBi0.5K0.5TiO3 have been fabricated by the conventional ceramic sintering technique, and their ferroelectric and piezoelectric properties have been studied. The results of X-ray diffraction reveal that Bi0.5K0.5TiO3 diffuses into the NaNbO3 lattices to form a new perovskite-type solid solution with orthorhombic symmetry. The addition of a small amount of Bi0.5K0.5TiO3 (x ≥ 0.025) transforms the ceramics from antiferroelectric to ferroelectric. The ceramic with x = 0.10 possesses the largest remanent polarization Pr and thus exhibits the optimum piezoelectric properties, giving d33 = 71 pC/N, kp = 16.6% and kt = 39.7%. The ceramics with low doping level of Bi0.5K0.5TiO3 are normal ferroelectrics and the ferroelectric-paraelectric phase transition becomes diffusive gradually with the doping level x of Bi0.5K0.5TiO3 increasing. Our results show the (1–x)NaNbO3–xBi0.5K0.5TiO3 ceramics is one of the good candidates for lead-free piezoelectric and ferroelectric materials.

Studies on mixed metal oxides solid solutions as heterogeneous catalysts

In this work, a series of perovskite-type mixed oxide LaMo xV1-xO3+δ powder catalysts (x = 0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1.0, with 0.5 < δ < 1.5), prepared by the sol-gel process and calcined at 750ºC, provide an attractive and effective alternative means of synthesizing materials with better control of morphology. Structures of resins obtained during the gel formation process by FT-IR spectroscopy and XRD analysis showed that all the LaMo xV1-xO3+δ samples are single phase perovskite-type solid solutions. The surface area (BET) between 2.5 - 5.0 m²/g (x = 0.1 and 1.0 respectively) increases with increasing Mo ratio in the samples. They show high purity, good chemical homogeneity, and lower calcinations temperatures as compared with the solid-state chemistry route. SEM coupled to EDS and thermogravimetric analysis/differential thermal analyses (TGA/DTA) have been carried out in order to evaluate the homogeneity of the catalyst. Finally, the experimental studies show that the calcination temperature and Mo content exhibited a significant influence on catalytic activity. Among the LaMo xV1-xO3+δ samples, LaMo0.7V0.3O4.2 showed the best catalytic activity for the topic reaction and the best activity and stability for ethane reforming at 850ºC under 8 bar.

Monoclinic phases and stress-relief conditions in (1 − x)Pb(Mg 1/3Nb 2/3)TiO 3– xPbTiO 3 solid solutions

A comparative study on heterophase states in perovskite-type solid solutions of (1 − x)Pb(Mg 1/3Nb 2/3)TiO 3– xPbTiO 3 is carried out for compositions near the morphotropic phase boundary. The conditions for mechanical stress relief at elastic matching of phases are analysed at x = const in a wide temperature range. The heterophase states concerned with the presence of the intermediate monoclinic phase are interpreted using the domain state–interface diagrams calculated for x = 0.28, 0.32 and 0.34. It is shown that optimum volume fraction parameters of the domains in the monoclinic phase of the B type are varied in relatively wide ranges and promote complete stress relief with cubic–monoclinic phase coexistence. Two scenarios of stress relief at x = 0.32 are considered in connection with different heterophase states (either tetragonal–monoclinic of the B type or tetragonal–monoclinic of the C type) in a wide temperature range. Possibilities of elastic matching of two polydomain phases (tetragonal–monoclinic of the B type) with almost equal relative widths of the domains in these phases are shown for x = 0.34. The active role of domains of the monoclinic phases in stress relief and forming the planar unstrained interfaces is discussed.

New Series of Solid-Solution Semiconductors (AgNbO3)1−x(SrTiO3)x with Modulated Band Structure and Enhanced Visible-Light Photocatalytic Activity

A novel series of solid-solution semiconductors (AgNbO3)1−x(SrTiO3)x (0 ≤ x ≤ 1) have been developed as highly visible-light-active photocatalysts for efficient O2 evolution and decomposition of organic pollutants. Rietveld refinement reveals that the perovskite-type solid solutions (AgNbO3)1−x(SrTiO3)x are crystallized in an orthorhombic system (0 ≤ x < 0.9) or a cubic system (0.9 ≤ x ≤ 1). In the mixed valent perovskites (AgNbO3)1−x(SrTiO3)x, the hybridization behaviors between the Ag 4d and O 2p orbitals and between the Nb 4d and Ti 3d orbitals play a crucial role in tuning the energy band structure (band gap, band edge, and bandwidth, etc.) and, thus, in tailoring the photophysical and photocatalytic properties. As a result of competition between the absorption ability to visible-light and the reductive/oxidative abilities, the highest visible-light activities for both O2 evolution and decomposition of gaseous 2-propanol (IPA) are realized over (AgNbO3)0.75(SrTiO3)0.25. In addition, very fine Ag parti...

Bi doping effect on the thermoelectric properties of perovskite-type Sr 0.7Ba 0.3PbO 3

Ceramics of perovskite-type solid solutions Sr 0.7Ba 0.3Pb 1− x Bi x O 3 with x = 0.00 – 0.25 were prepared, and the electrical conductivity and Seebeck coefficient were measured in a temperature range 373–1073 K to elucidate the Bi doping effect on the thermoelectric properties of the Sr 0.7Ba 0.3PbO 3, which was an n -type semi-metal. The itinerant conduction behavior was observed for the materials with 0.00 ≤ x ≤ 0.10 , in which the Bi atoms were doped as Bi 4+ to give electron carriers and mixing of Bi6s orbitals to the conduction band composed of Pb6s–O2p anti-bonding orbitals. The materials changed from semi-metals for x ≤ 0.05 to a metal for x = 0.10 upon the electron doping. The localized conduction behavior occurred and enlarged with increasing Bi content for the materials with 0.15 ≤ x ≤ 0.25 . This change from itinerant to localized was probably ascribed to the Bi disproportionation from Bi 4+ to Bi 4+δ and Bi 4−δ beyond x = 0.10 , which enlarged with increasing Bi content. Thermoelectric power factors decreased with the Bi doping, mainly due to the large decrease in the absolute values of the Seebeck coefficient, and were maximized for the Bi-undoped Sr 0.7Ba 0.3PbO 3 showing 1.7×10 −4 to 3.9×10 −4 W m −1 K −2.

Preparation of Perovskite-Type Sr1-xBaxPbO3 Ceramics by an Oxalate Coprecipitation Method and the Thermoelectric Properties

An oxalate coprecipitation method was applied to prepare dense ceramics of perovskite-type Sr1-xBaxPbO3 solid solutions with x = 0.0∼0.5, and the electrical conductivity and Seebeck coefficient were measured at high temperatures to estimate the thermoelectric power factors. Sr-Ba-Pb oxalates were coprecipitated from starting nitrate solutions with molar ratios of metallic ions controlled to Pb/Sr1-xBax = 1.05 and calcined at 700°C to obtain fine oxide powders. The small amount of PbO particles, which were dispersed well in the calcined powders composed mainly of SrPbO3 and BaPbO3, formed liquid phase during the sintering and led to the formation of the dense Sr1-xBaxPbO3 ceramics. The thermoelectric power factors of the Sr1-xBaxPbO3 ceramics with x = 0.0∼0.5 were estimated to be 1.0×10−4∼3.6×10−4 Wm−1K−2 in the temperature range 373∼1073 K and the value was maximized for the Sr0.7Ba0.3PbO3 ceramic. This study suggests that the present oxalate coprecipitation method is a simple and useful way to prepare dense Sr1-xBaxPbO3 ceramics showing comparatively high thermoelectric power factors.

Relationship between MPB and Emergence of Structural Boundary in Cubic Phase of Pb-Based Perovskite-Type Solid Solutions PZT and PZN-PT

Relationship between MPB and Emergence of Structural Boundary in Cubic Phase of Pb-Based Perovskite-Type Solid Solutions PZT and PZN-PT