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Rare earth silicates are promising environmental/thermal barrier coating (E/TBC) materials facing severe CMAS (CaO‐MgO‐Al2O3‐SiO2) corrosion. Previous studies mainly focused on the intrinsic properties of precorrosion coatings, but there were few studies on their CMAS corrosion products that play a crucial role in the performance of coatings in postservice stage. In this work, the mechanical and thermal properties of nine corrosion products between lutetium silicates and CMAS are studied using first‐principles calculations. Their differences of elastic stiffness are attributed to the different crystal structures and bonding strength. The T:O ratio is identified as a factor of the crystal structure for silicate products, and it has a good correlation with their elastic stiffness. Moreover, the divergences of thermal conductivity are dominated by three essential factors, that is, atomic vibration intensity, lattice vibrational anharmonicity, and complexity of crystal structure. Compared with rare earth silicates, six products, that is, the α‐CaSiO3, β‐CaSiO3, Ca2MgSi2O7, Ca2Al2SiO7, CaAl2Si2O8, and Ca2Lu8(SiO4)6O2, showing good damage tolerance and low thermal conductivities, are predicted to be advantageous to E/TBCs. These discoveries reveal the mechanical/thermal properties of corrosion products between lutetium silicates and CMAS and are expected to support the future researches on the performance of E/TBC in the postservice stage. [ABSTRACT FROM AUTHOR]

RE2SiO5 (RE = Yb and Lu) are significant environmental barrier coating (EBC) materials, in which surface and oxygen vacancy play crucial roles in their structural stability and functionality. In this work, the structural configuration and thermodynamics of (1 0 0), (0 1 0), and (0 0 1) surfaces of RE2SiO5 are investigated by first‐principles calculations. The (0 0 1) surface is preferred energetically, which is attributed to the weak bond broken environment and large rare‐earth polyhedron distortion on this surface. Moreover, the formation energies of various oxygen vacancies on the stable (0 0 1) surface are estimated and the optimal location for oxygen vacancies is held by the [SiO4] tetrahedron. The oxygen vacancies are more likely to segregate on the surface because of the lower formation energies on the surfaces compared with those in the bulk. These findings are expected to enable the development of RE2SiO5‐based EBCs by tuning grain size and/or thin film growth orientation. [ABSTRACT FROM AUTHOR]

Herein, high-density La0.7(Ca0.205Sr0.095)MnO3:xAg2O composites (LCSMO:xA, 0.0 ≤ x ≤ 0.5) are successfully fabricated by using a combination of sol–gel and solid-state methods. The electromagnetic properties are investigated using a phenomenological percolation (PP) model, double exchange (DE) mechanism and Jahn–Teller (JT) effect. Moreover, X-ray diffraction (XRD) and scanning electron microscopy (SEM) are employed to analyze the crystal structure and morphology of LCSMO:xA composites. The distortion of MnO6 octahedron is confirmed via Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Also, the valence states and ionic stoichiometry are assessed by using X-ray photoemission spectroscopy (XPS). The results reveal that Ag+ ions, occupying the A-sites, significantly influence the crystal structure, formation of Mn3+/Mn4+ pairs, and distortion of MnO6 octahedron. Furthermore, the presence of metallic Ag at grain boundaries (GBs) improves the conductivity of LCSMO:xA composites by providing the desired conductive channels. At the Ag2O content of x = 0.2, the maximum temperature coefficient of resistance (TCR) of the resistivity is found to be 17.26% K−1 at 299.9 K, whereas the low-field magnetoresistance (MR, 0.8 T magnetic field) is found to be 30.34% at 300.93 K. This room-temperature TCR value is the highest among those for the studied perovskite-structured manganese oxide composites. These results confirm that the room-temperature TCR and MR values of LCSMO:xA composites can be tuned by optimizing the content of metallic Ag and Ag+ ions. [ABSTRACT FROM AUTHOR]

Herein, the influence of Sr doping on chemical composition, microstructure, and electrical transport properties of La 0.67 Ca 0.33- x Sr x MnO 3 (LCSMO, 0.06 ≤ x ≤ 0.11) polycrystalline ceramics is systematically investigated. The study was performed by using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), elemental mapping, energy dispersive spectrometry (EDS), X-ray photoemission spectroscopy (XPS), and four-probe method (ρ - T). XRD results verified the synthesis of high-purity orthogonal perovskite structure with Pnma space group. EDS and XPS results confirmed presence and uniform distribution of La, Ca, Sr, Mn and O. Furthermore, ρ - T curves indicated that the resistivity decreased with increasing Sr content, whereas metal-insulator transition temperature (T MI) gradually increased. Moreover, cell volume (V) and electron bandwidth (W) increased with the increase in Sr content, which effectively reduced the resistivity of LCSMO ceramics. One should note that double exchange (DE) enhancement between Mn3+ and Mn4+ is responsible for gradually increasing T MI. Finally, maximum TCR value of 14.3% K−1 was achieved at x = 0.08, which rendered TCR peak temperature of 299.0 K. High room-temperature TCR of LCSMO ceramics is promising for next-generation infrared bolometers, operating at room-temperature. [ABSTRACT FROM AUTHOR]

In this study, the doping effects of silver on the structural, electrical and magnetic properties of polycrystalline La0.625Ca0.285Sr0.09MnO3:Agx (LCSMO:Agxx = 0, 0.10, 0.20, 0.25, and 0.30) ceramics were investigated and the results were discussed. The ceramic specimens were prepared by the sol–gel method followed by sintering at 1673 K for 14 h. The optimization of ceramic properties, such relative high temperature coefficient of resistance (TCR) in the vicinity of room temperature was obtained by varying the Ag doping content. X-ray diffraction indicated that all specimens crystallized in typical orthorhombic perovskite phase with Pnma space group. Rietveld refinement data showed that structural parameters, such as Mn–O bond length, Mn–O−Mn bond angles and cell volumes were slightly modified when Ag content increased. Scanning electron microscopy depicted reduced grain boundaries and increased grain size when Ag content rose. Resistivity dependence of temperature curves (R−T) of LCSMO:Agx specimens were investigated by standard four-probe method, and R−T curves indicated decline in resistivity with Ag2O content. The specimen with x = 0.25 illustrated relatively high TCR value reaching 4.60%/K near room temperature (310.06 K). X-ray photoelectron spectroscopy revealed that Ag+ could increase Mn4+ ion concentration since Ag+ ion may replace La3+, Ca2+ and Sr2+ ions at A-sites. The magnetoresistance measured at low magnetic field of 0.8 T suggested enhancement in low field magnetoresistance of LCSMO:Agx ceramics with x. Overall, the prepared ceramics look promising for applications in bolometric infrared detectors. [ABSTRACT FROM AUTHOR]

Polycrystalline La 0.67 Ca 0.33- x Ag x MnO 3 (LCAMO, x = 0, 0.06, 0.15, 0.18, and 0.24) ceramics were fabricated by conventional sol-gel route at relatively low sintering temperature of 1100 °C for 12 h. Effects of silver content (x) on crystal structure, grain size, resistivity and magnetic properties of as-prepared LCAMO specimens were investigated by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), elemental mapping and energy dispersive spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), and standard four-probe method (ρ - T). The data from XPS, XRD and EDS revealed that silver existed as Ag+ ions in the lattice matrix position of LCAMO ceramics. Broad metal-insulator transition temperature (T MI) values ranging from 267.0 K (x = 0) to 302.6 K (x = 0.24) were obtained with LCAMO specimens prepared with variable Ag+ added contents. Peak temperature coefficient of resistivity (TCR) enhanced from 4.1% K−1 at 263.2 K (for x = 0) to 10.9% K−1 at 278.5 K (for x = 0.18), and reached 7.5% K−1 at room-temperature (295.9 K) for x = 0.24. Meanwhile, magnetoresistance (MR) of materials reached 17.7% at room-temperature (299.2 K) for x = 0.24. Overall, these findings demonstrated that Ag doping was beneficial for improving electrical and magnetic properties of LCAMO materials. In summary, LCAMO ceramics achieved RT-TCR and MR at optimal Ag stoichiometric ratio, promising for applications in infrared bolometers or magnetic sensors. [ABSTRACT FROM AUTHOR]

In this work, polycrystalline La0.845Sr0.155MnO3:Ag0.4 (LSMO:Ag) ceramics were synthesized via a combined sol–gel and solid-state method with various sintering times. The structure and unique electrical and magnetic properties of the synthesized ceramics were examined in detail. The optimized sintering temperature was determined to be 1723 K. At this temperature, by changing the sintering time from 5 to 14 h, the temperature coefficient of resistivity (TCR) and the magnetic resistance (MR) of the LSMO:Ag samples could be quickly improved. The results show that La3+ and Sr2+ ions were gradually substituted by Ag+ ions with increasing sintering time. The substitution resulted in changes to the Mn3+–O–Mn4+ pairs and a distortion of the MnO6 octahedron, which could be attributed to the double exchange (DE) and Jahn–Teller (JT) effects. At a sintering time of t = 10 h, a peak TCR value of 17.82% K−1 was attained and was achieved at room-temperature (Tk, 299.9 K). This work demonstrates an effective approach to obtain high TCR and MR values at room-temperature for uncooled manganite devices by optimizing the sintering time. [ABSTRACT FROM AUTHOR]