SrO2 Research Articles

Thermophysical Properties of Gd<sub>2</sub>O<sub>3</sub> Doped SrHfO<sub>3</sub> Ceramic

Gd2O3 (10mol%) doped SrHfO3 (Sr (Hf0.9Gd0.1)O2.95) was synthesized by solid state reaction method. The phase stability of the synthesized Sr (Hf0.9Gd0.1)O2.95 powder at high temperature of 1450 oC for a long period and in a temperature range of RT-1400 oC was characterized by XRD and DSC, respectively. The thermal expansion coefficients (TECs) of bulk Sr (Hf0.9Gd0.1)O2.95 were recorded by a high-temperature dilatometer, indicating that the phase transitions of SrHfO3 are suppressed remarkably by doping Gd2O3. The thermal conductivity of bulk Sr (Hf0.9Gd0.1)O2.95 at 1000 oC is ~1.95 W/m·K, which is ~11% lower than that of bulk 8YSZ.

Hot corrosion behaviour of double rare-earth oxides co-doped SrZrO3 coatings in molten sulphate–vanadate salt at 900°C

Thermal barrier coatings (TBCs) of Sr(Y0·05Yb0·05Zr0·9)O2·95 (SYYZ) and Sr(Y0·05Gd0·05Zr0·9)O2·95 (SYGZ) were prepared by air plasma spraying. The present study investigated the hot corrosion performance of the SYYZ and SYGZ coatings in the presence of molten Na2SO4+V2O5 salts at 900°C for 10 h. Changes in the coatings were studied using a scanning electron microscope (SEM) to observe the microstructure and X-ray diffraction (XRD) technique to analyse the phase composition. XRD results together with SEM observations indicated that, both the SYYZ and SYGZ coatings reacted with the molten Na2SO4+V2O5 salts at 900°C to form SrSO4, Sr3V2O8, YbVO4 and SrSO4, Sr3V2O8, GdVO4 respectively. The m-ZrO2 was also developed due to the decomposition of both the SYYZ and SYGZ coatings during the corrosion process. The excess Yb2O3 and Gd2O3 in the as sprayed SYYZ and SYGZ coatings respectively, can aggravate the degradation of both the SYYZ and SYGZ coatings by molten Na2SO4+V2O5 salts. The phase transformation and chemical interaction are the main corrosion mechanisms for deterioration of the SYYZ and SYGZ coatings. The YSZ coating was also investigated under the same corrosion condition for comparison.

Hot corrosion behaviors of SrZrO3 ceramic co-doped with Y2O3 and Yb2O3 in molten Na2SO4, V2O5, and Na2SO4+V2O5 salts mixture

Abstract The hot corrosion behaviors of Sr(Y0.05Yb0.05Zr0.9)O2.95 (SYYZ) ceramic were investigated in Na2SO4, V2O5, and Na2SO4 + V2O5 salts mixture, respectively. Na2SO4 did not react with SYYZ ceramic at 900, 950 and 1000 °C. m-ZrO2, YVO4 and YbVO4 were the main corrosion products on the SYYZ ceramic surface in V2O5 at 800 and 900 °C, whereas Sr3V2O8 and t-ZrO2 appeared at 1000 °C. In Na2SO4 + V2O5 salts mixture, the corrosion products were Sr3V2O8 and t-ZrO2 at 800 and 900 °C on the SYYZ ceramic surface, however, a new phase of SrZrO3 developed at 1000 °C. The phase transformation and chemical interaction are the primary corrosion mechanisms for degradation of SYYZ ceramic.

Y2O3 and Yb2O3 Co-doped Strontium Hafnate as a New Thermal Barrier Coating Material

Y2O3 and Yb2O3 co-doped strontium hafnate powder with chemistry of Sr(Hf0.9Y0.05Yb0.05)O2.95 (SHYY) was synthesized by a solid-state reaction at 1450 °C. The SHYY showed good phase stability not only from 200 to 1400 °C but also at a high temperature of 1450 °C for a long period, analyzed by differential scanning calorimetry and x-ray diffraction, respectively. The coefficient of thermal expansion of the sintered bulk SHYY was recorded by a high-temperature dilatometer and revealed a positive influence on phase transitions of SrHfO3 by co-doping with Y2O3 and Yb2O3. The thermal conductivity of the bulk SHYY was approximately 16% lower in contrast to that of SrHfO3 at 1000 °C. Good chemical compatibility was observed for SHYY with 8YSZ or Al2O3 powders after a 24 h heat treatment at 1250 °C. The phase stability and the microstructure evolution of the as-sprayed SHYY coating during annealing at 1400 °C were also investigated.

Preferential leaching of Sr from mixed (Th/Sr) oxide

Preferential leaching of Sr from irradiated thorium may play an important role to facilitate the management of high level waste as well as provide a new route to recover valuable fission product 90Sr which has potential applications as (a) compact heat source and (b) as parent radionuclide for 90Y, used in therapeutic radiopharmaceuticals. In the present work, leaching of Sr from (Th,Sr)O2 in nitric acid and perchloric acid medium has been investigated as a function of acidity as well as refluxation time. It was interesting to observe that quantitative leaching of Sr(II) is possible even at 0.01M HClO4 where leaching of Th is negligible (∼0.01%). Leaching behavior of other metal ions, like Pd(II), Y(III), and Zr(IV), representing few major fission products was also investigated.

Magnetic and structural properties of BiFeO3 thin films grown epitaxially on SrTiO3/Si substrates

The integration of oxides with semiconductors is important for the technological advancement of the next generation electronics. Concomitant ferroelectric and antiferromagnetic (AF) behavior is demonstrated in single crystal BiFeO3 (BFO) films grown on 20 nm SrTiO3 (STO) virtual substrates on Si(100) using molecular beam epitaxy (MBE). STO thin films are grown in an oxide MBE chamber by co-deposition of Sr, Ti, and molecular O2. Careful control of the O2 during nucleation produced commensurate growth of STO on Si. The sequence of the steps allows for the suppression of an amorphous SiO2 layer. This STO(20 nm)/Si structure was used as a virtual substrate for MBE deposition of BFO on Si without breaking vacuum. BFO was deposited using Fe and O2 plasma with an overpressure of Bi flux, the growth rate was controlled by the incoming Fe flux. The reflection high energy electron diffraction image shows a 2-D growth front with a 6-fold surface reconstruction under optimized O2 pressure of 5 × 10−8 mbar. Cross-sectional transmission electron microscopy (TEM) confirms the high crystallinity of the films and shows sharp, atomically flat interfaces. The selected area diffraction pattern (SADP) reveals that BFO grows in a distorted rhombohedral crystal structure. X-ray diffraction does not show formation of second phases and is consistent with the TEM and SADP results. The BFO films show AF behavior with a Neel temperature that exceeds 350 K, as expected (TN = 673 K) and with a residual ferromagnetic behavior that decreases with film thickness and is consistent with the G-type AF due to the canted spins. The saturation magnetization per unit volume for a 40 nm thick film was 180 emu/cm3 at an in-plane magnetic field of 8 kOe. The ferroelectric behavior of the films was verified using piezoresponse force microscopy.

Double Rare-Earth Oxides Co-doped Strontium Zirconate as a New Thermal Barrier Coating Material

Y2O3 and Yb2O3 co-doped strontium zirconate with chemistry of Sr(Zr0.9Y0.05Yb0.05)O2.95 (SZYY) was synthesized and had a minor second phase of Yb2O3. The SZYY showed good phase stability not only from room temperature to 1400 °C but also at high temperature of 1450 °C for a long period, analyzed by thermogravimetry-differential scanning calorimetry and x-ray diffraction, respectively. The coefficients of thermal expansion (CTEs) of the sintered bulk SZYY were recorded by a high-temperature dilatometer and revealed a positive influence on phase transitions of SrZrO3 by co-doping with Y2O3 and Yb2O3. The thermal conductivities of SZYY were at least ~30% lower in contrast to that of SrZrO3 and 8YSZ in the whole tested temperature range. Good chemical compatibility was observed for SZYY with 8YSZ or Al2O3 powders after a 24 h heat treatment at 1250 °C. The phase stability and the microstructure evolution of the as-sprayed SZYY coating during annealing at 1400 °C were also investigated.

A novel approach for preferential recovery of Sr from (Sr, Th)O2

Quantitative leaching of Sr from homogeneous and calcined (Th,Sr) O2 in dilute perchloric acid medium suggests the possibility of reducing the hazardousness of discharged nuclear fuel by separation of 90Sr, a prominent fission product at dissolution stage itself rather than the conventional approach of its recovery from high level nuclear waste. Apart from mitigating the radiotoxicity of the nuclear waste, recovered 90Sr can be employed as a compact heat source and as parent radionuclide for 90Y (used in therapy radiopharmaceuticals), provided it can be made available at desired high purity. Leaching behavior of few other fission products was also investigated to quantify their contamination in leached Sr. Feasibility of employing extraction chromatography using Sr selective resin was explored in perchloric acid medium. In this context, the distribution coefficients of 85Sr(II), Th (IV), Zr(IV), Y(III), Pd(II) as well as 152Eu(III) and 137Cs (I) were determined under varying nitric acid/perchloric acid concentration and under varying loading conditions of metal ions. Perchloric acid medium appears better than nitric acid medium for preferential leaching of Sr from (Th,Sr)O2 as well as for uptake of Sr by Sr selective chromatographic resin.

Recovery and purification of Sr(II) in perchloric acid medium

Perchloric acid was found to be a suitable medium for the quantitative leaching of Sr(II) from homogeneous and calcined (Th,Sr)O2 particularly with respect to the contamination from Th(IV). 90Sr is a cause of major concern to the environment due to its long half life (28.6 years), significant abundance in large inventory of spent nuclear fuels (~350 thousand tons) awaiting geological disposal and its chemical similarity to Ca(II), an essential element for the living beings. Application of 90Sr as a parent radionuclide for 90Y (used in therapy radiopharmaceuticals) is possible provided it can be made available at desired high purity. In this context, the distribution coefficients of Sr(II), Th(IV), Zr(IV), Y(III), 152Eu(III) and 137Cs(I) were determined using Sr selective crown ether 4,4′(5′)-di-tert-butyl-dicyclohexano-18-crown-6 by solid–liquid extraction in perchloric acid medium. Feasibility of employing extraction chromatography using Sr selective resin for the recovery and purification of Sr(II) from leached perchloric acid medium was explored. Perchloric acid medium is better than nitric acid medium for the uptake of Sr by Sr selective chromatographic resin under varying loading conditions of Sr(II). Similarly pH 2 solution appears better eluent of Sr(II) than distilled water. Present work offers a novel approach for setting up a 90Sr–90Y generator.

Crystal structure of Sr6Y2Al4O15: XRD refinements and first-principle calculations

The ternary oxide phase Sr6Y2Al4O15 (SYA) was synthesized and the crystal structure was determined by using the X-ray powder diffraction data. Structure of the phase can be considered as an oxygen-deficient perovskite Sr(Y1/3Al2/3)O2.5 and has a monoclinic C2 (S.G. No. 5) unit cell with the unit cell parameters: a=17.597(1)Å, b=5.7408(1)Å, c=7.6860(1)Å, β=90.7659(3)°, Vcell=776.37(1)Å3, Z=2. By bond parameter analysis and first-principle calculations, we confirmed the reasonability of our crystal structure model. According to the calculated band structure, SYA has an indirect band gap ∼4.3eV and a direct band gap ∼4.4eV, which is wide to be transparent to UV and visible lights. We also synthesized other rare-earth isomorphs Sr6Ln2Al4O15 (Ln=Tb, Dy, Ho, Er, Tm, Yb and Lu) and obtained their cell parameters.

Thermophysical Properties of Y<SUB>2</SUB>O<SUB>3</SUB> and Gd<SUB>2</SUB>O<SUB>3</SUB> Co-doped SrZrO<SUB>3</SUB> Thermal Barrier Coating Material

Y2O3 (5mol%) and Gd2O3 (5mol%) co-doped SrZrO3 (Sr(Zr0.9Y0.05Gd0.05)O2.95, SZYG) was synthesized by solid state reaction method. The phase stability of the SZYG powder synthesized at high temperature of 1450℃ for a long period and at temperature range of 200−1400℃ was characterized by XRD and DSC, respectively. The coefficients of thermal expansion (CTEs) of bulk SZYG recorded by a high-temperature dilatometer show that the phase transitions of SrZrO3 is suppressed remarkably by co-doping Y2O3 and Gd2O3. The thermal conductivity of bulk SZYG at 1000℃ is 1.36 W/(m·K), which is 35% lower than that of bulk SrZrO3 and 8YSZ. The good chemi- cal compatibility of SZYG with 8YSZ and Al2O3, is detected after heat-treatment at 1250℃ for 24 h.

Structural, luminescence and EPR studies on SrSnO3 nanorods doped with europium ions

The present study describes the structural and luminescent properties of SrSnO(3) nanorods containing Eu(3+) ions. Based on Rietveld refinement of XRD patterns corresponding to both undoped and europium doped SrSnO(3) nanorods, it is inferred that the average bond lengths of Sr-O1 linkages, which have a square planar geometry around Sr(2+) in the SrO(12) polyhedra present in SrSnO(3), remained unaffected with Eu(3+) incorporation into the lattice. However, the average bond lengths of shorter Sr-O2 linkages increase and longer Sr-O2 linkages decrease with Eu(3+) doping into the SrSnO(3) lattice. A lack of variation in the lattice parameters of SrSnO(3) with doped Eu(3+) ions is explained based on mutually compensating changes in the average bond lengths of the Sr-O2 linkages in the unit cell. Luminescence studies have confirmed that Eu(3+) ions occupy the centrosymmetric Sr(2+) site only up to 2 at%, beyond which Eu(3+) ions exist in a significantly distorted environment (grain boundaries). Beyond 3%, incorporation of Eu(3+) ions into the SrSnO(3) lattice leads to the formation of a Eu(2)Sn(2)O(7) phase. From the EPR studies it is confirmed that around 5% of the incorporated Eu(3+) ions get converted to Eu(2+) ions and they occupy Sr(2+) sites in the lattice.

Thermodynamic restrictions on mechanosynthesis of strontium titanate

Chemical potential phase stability diagrams were calculated from relevant thermodynamic properties and used to predict the thermodynamic driving force under prospective conditions of room temperature mechanosynthesis. One analysed the dependence of chemical potential diagrams on temperature and partial pressure of evolving gases such as oxygen or carbon dioxide, as expected on using strontium peroxide or strontium carbonate as precursor reactants for the alkali earth component. Thermodynamic calculations were also obtained for changes in titania precursor reactants, including thermodynamic predictions for reactivity of strontium carbonate with amorphous titania. Experimental evidence showed that strontium titanate can be obtained by mechanosynthesis of strontium carbonate+anatase mixtures, due to previous amorphization under high energy milling. Ability to perform mechanosynthesis with less energetic milling depends on the suitable choice of alternative precursor reactants, which meet the thermodynamic requirements without previous amorphization; this was demonstrated by mechanosynthesis from anatase+strontium peroxide mixtures.

Double-q Order in a Frustrated Random Spin System

We use the three-dimensional Heisenberg model with site randomness as an effective model of the compound Sr(Fe1−xMnx)O2. The model consists of two types of ions that correspond to Fe and Mn ions. The nearest-neighbor interactions in the ab-plane are antiferromagnetic. The nearest-neighbor interactions along the c-axis between Fe ions are assumed to be antiferromagnetic, whereas other interactions are assumed to be ferromagnetic. From Monte Carlo simulations, we confirm the existence of the double-q ordered phase characterized by two wave numbers, (πππ) and (ππ0). We also identify the spin ordering pattern in the double-q ordered phase.

ChemInform Abstract: Fe‐Site Substitution Effect on the Structural and Magnetic Properties in SrFeO2.

AbstractThe substitution effect on structural and magnetic properties of Sr(Fe1‐xMx)O2 (M: Co, Mn) is characterized by synchrotron XRD, neutron diffraction, and 57Fe Moessbauer spectroscopy.

Sc<sub>2</sub>O<sub>3</sub> and Gd<sub>2</sub>O<sub>3</sub> Co-Doped Strontium Zirconate as a New Thermal Barrier Coating Material

An advanced ceramic material of perovskite structure, Sc2O3 (5 mol%)and Gd2O3 (5 mol%) co-doped SrZrO3, was investigated as a material for thermal barrier coating (TBC) applications. Sr(Zr0.9Sc0.05Gd0.05)O2.95 (SZSG) was synthesized using ball milling prior to solid-state sintering, and had a minor second phase of Gd2O3. The material showed good phase stability not only from room temperature to 1400°C, but also at high temperature of 1450°C for a long period, analyzed by DSC and XRD, respectively. The thermal expansion coefficients (TECs) of the sintered bulk SZSG were recorded by a high-temperature dilatometer and revealed a positive influence on phase transitions of SrZrO3 by co-doping Sc2O3 and Gd2O3. The thermal conductivity of SZSG had much lower values in contrast to that of SrZrO3 and Sr(Zr0.8Gd0.2)O2.9 in whole tested temperature range. The good chemical compatibility was observed for SZSG with 8YSZ or Al2O3 powders. All the results revealed that SZSG might be a potential material for TBC applications at higher temperatures compared with 8YSZ.

Fe-Site Substitution Effect on the Structural and Magnetic Properties in SrFeO2

We investigated the Fe-site substitution effect on the structural and magnetic properties of the infinite layer iron oxide Sr(Fe(1-x)M(x))O(2) (M = Co, Mn) using synchrotron X-ray diffraction, neutron diffraction, and (57)Fe Mössbauer spectroscopy. Both systems have a similar solubility limit of x ≈ 0.3, retaining the ideal infinite layer structure with a space group of P4/mmm. For the Fe-Co system, both in-plane and out-of-plane axes decrease linearly and only slightly with x, reflecting the ionic radius difference between Fe(2+) and Co(2+). For the Fe-Mn system the lattice evolution also follows Vegard's law but is anisotropic: the in-plane axis increases, while the out-of-plane decreases prominently. The magnetic properties are little influenced by Co substitution. On the contrary, Mn substitution drastically destabilizes the G-type magnetic order, featured by a significant reduction and a large distribution of the hyperfine field in the Mössbauer spectra, which suggests the presence of magnetic frustration induced presumably by a ferromagnetic out-of-plane Mn-Fe interaction.

Iron(II)-Thiolate S-Oxygenation by O2: Synthetic Models of Cysteine Dioxygenase

The synthesis of structural and functional models of the active site of the nonheme iron enzyme cysteine dioxygenase (CDO) is reported. A bis(imino)pyridine ligand scaffold was employed to synthesize a mononuclear ferrous complex, Fe(II)(LN(3)S)(OTf) (1), which contains three neutral nitrogen donors and one anionic thiolato donor. Complex 1 is a good structural model of the Cys-bound active site of CDO. Reaction of 1 with O(2) results in oxygenation of the thiolato sulfur, affording the sulfonato complex Fe(II)(LN(3)SO(3))(OTf) (2) under mild conditions. Isotope labeling studies show that O(2) is the sole source of O atoms in the product and that the reaction proceeds via a dioxygenase-type mechanism for two out of three O atoms added, analogous to the dioxygenase reaction of CDO. The zinc(II) analog, Zn(LN(3)S)(OTf) (4), was prepared and found to be completely unreactive toward O(2), suggesting a critical role for Fe(II) in the oxygenation chemistry observed for 1. To our knowledge, S-oxygenation mediated by an Fe(II)-SR complex and O(2) is unprecedented.

Calculation of the kinetic parameters of dehydration of lithium peroxide monohydrate in nonisothermic regime by derivatographic method

The dehydration of lithium peroxide monohydrate was studied by derivatography under nonisothermic conditions for the calculation of main kinetic parameters in the temperature range 90–146°C. Experimental conditions (sample size and the linear heating rate) caused by thermoconductivity of the object under investigation were determined. It is shown that the process under study proceeds according to the kinetic law close to the first order one (n = 0.85±0.03). Values of the activation energy and the pre-exponential factor [Ea = 86.0±0.8 kJ mol−1, k0 = (2.19±0.16)×1011 min−1] were obtained. A suggestion was formulated that the dehydration mechanism of lithium peroxide monohydrate was analogous to that of the hydrates of the alkaline earth metal (calcium, barium, and strontium) peroxides.

Combustion synthesis of alkaline-earth substituted lanthanum manganites; LaMnO3, La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3

Alkaline-earth substituted lanthanum manganites La1 − xAxMnO3 (A = Ca, Sr; x = 0, 0.4) were synthesized in air by self-propagating high-temperature synthesis (SHS): a combustion process involving the reaction of lanthanum(III) oxide, calcium oxide (or carbonate), strontium peroxide, manganese metal powder and sodium perchlorate. A very sensitive thermal imaging method was used to study the combustion characteristics of the SHS-process. This method is based on the continuous measurement of the combustion process using an IR-camera and software developed by MIKRON Instrument Co., Inc. (M9100 Pyrovision Series – Imaging Pyrometer). X-Ray powder diffraction, scanning electron microscopy (SEM)/energy dispersive analysis by X-rays (EDAX), infrared spectroscopy and vibrating sample magnetometry were carried out on all samples. X-Ray diffraction data showed that single-phase orthorhombic LaMnO3 and monoclinic La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3 were formed. Magnetic properties were found to transform from antiferromagnetic for LaMnO3 to weak ferromagnetic for La0.6Ca0.4MnO3 to strong ferromagnetic for La0.6Sr0.4MnO3. The experimental results show the SHS route is useful for the synthesis of multicomponent Mn-based oxides. The thermal imaging work enables accurate monitoring of the SHS combustion process and enabled velocity of propagation, maximum temperature, cooling rates, synthesis wave width and synthesis wave path to be determined with high precision.