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To facilitate the repairing and connecting processes for titanium superalloys, an advanced high-temperature resistant adhesive that can be converted to a composite of intermetallics and ceramics was prepared by modifying aluminum phosphate-based adhesive with various additives. The composition evolution of the adhesive, the structure changes in the bonding layer, the reaction process at interfaces and the fracture mode of joints are comprehensively studied to explore the bonding mechanism. The results showed that the chemical bonding based on the formation of TiSi and Ti5Si4 started to work at 600 °C, and became the crucial bonding mechanism at higher temperatures. A diffusion reaction layer with size up to 6 μm effectively alleviated the difference of composition and performance between alloy substrate and adhesive. From RT to 900 °C, the coefficient of thermal expansion (CTE) of adhesive matched well with that of alloy substrates, and the difference of their CTE was always lower than 2 × 10−6 k−1. The bonding strength reached ~16 MPa after pre-treatment at 900 °C without pressure, and remained over 13 MPa within the common operating temperature range (400–600 °C) of TC4 alloys. Without any pre-treatment, the adhesive could still provide above 5 MPa in range of RT-600 °C.

Photoluminescence materials with reversible luminescence regulation properties have great potential for applications in photoswitches, optical sensing, and high-density optical data storage devices. In this work, a series of Pr3+-doped Bi4Ti3O12 (BiT) ceramics were synthesized by a high-temperature solid-phase reaction method. It is well known that BiT is the most famous one within the Aurivillius ferroelectric (FE) system. Previous works routinely focused on the FE-related properties of BiT-based compounds, but little attention has been devoted to the luminescence, especially the luminescence modulation performance. Here, a large and reversible photoluminescence modulation by alternating visible light irradiation and thermal stimulus based on photochromic (PC) process was achieved. Meanwhile, the influence of sintering temperature on the luminescence modulation behavior was also illustrated. The luminescence regulation properties of the Pr3+-doped BiT ceramics prepared at optimized sintering temperature were investigated in detail. The mechanisms connected to the luminescence, luminescence manipulation, and PC effect were discussed. It is believed that Pr3+-doped BiT materials can be utilized as a kind of ideal optical medium for future information storage device.

Up-conversion (UC) phosphors with multiple functions are highly desirable for many potentially technological applications which can stimulate the miniaturization and multipurpose of modern devices. In this work, Tm3+- and Yb3+-codoped SrBi4Ti4O15 (SBT:xTm3+/Yb3+) nanoparticles have been first synthesized by a convenient EDTA-citrate method. The structures and morphologies of SBT:xTm3+/Yb3+ were measured by powder X-ray diffraction, Fourier transform infrared reflectivity spectra and scanning electron microscope. Under 980 nm excitation, SBT:xTm3+/Yb3+ exhibited strong near-infrared (NIR) and weak visible emissions. The UC emissions were unveiled to be tightly related to the Tm3+ concentration and the optimum concentration was determined as x = 0.01. The possible UC mechanism was proposed. Importantly, based on thermo-responsive fluorescence intensity ratio approach, the optical thermometric properties were characterized in the temperature range between 313 and 573 K. The maximum sensitivity of SBT:0.01Er3+/Yb3+ UCNPs was obtained as 7.5 × 10−4 K-1. Besides, excellent repeatability and stability were also realized by the thermal-cycling measurement. Furthermore, prominent photo-thermal (PT) effect was also achieved with a temperature coefficient being 0.81 °C∙mm2/mW. Under periodic laser stimulation, the PT effect of the sample displayed regular response, indicating that the PT effect can be expediently controlled by 980 nm laser. These results indicate that SBT:xTm3+/Yb3+ UCNPs could be potential candidates for temperature sensors and PT agents.

Er-doped Sr 2 Bi 4 Ti 5 O 18 (SBT- x ) ceramics were synthesized via a solid-state reaction method, and their structure, up-conversion luminescence (UCL), temperature sensing performance and ferroelectric behaviors were investigated. The obtained SBT- x samples crystallize in the polar orthorhombic phase, with space group B2cb. Under 980 nm excitation, bright green and weak red emissions are observed which correspond to the transitions from 2 H 11/2 / 4 S 3/2 and 4 F 9/2 to 4 I 15/2 level, respectively. The optimal doping concentration of Er 3+ in SBT host is determined as 0.08. The critical energy transfer distance ( R c ) is about 20.57 A and the major interaction mechanism among Er 3+ ions is determined as the d–d interaction. A possible UCL mechanism is proposed in light of the dependence of emission intensities on pumping power. Furthermore, optical temperature sensing properties are also investigated according to the fluorescence intensity ratio (FIR) of green emissions at 527 and 550 nm in the temperature range from 303 K to 573 K. The maximum sensing sensitivity is found to be 0.0042 K −1 . Additionally, the response of SBT- x to external electric field stimuli is also confirmed. It is believed that SBT- x has potential application as optical temperature sensing materials.

In this paper, Zn 2 SnO 4 nanospheres were prepared using hexadecyltrimethylammonium bromide (CTAB) and sodium citrate as co-templates. The crystal structure and morphology of as-prepared Zn 2 SnO 4 product were characterized by X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FE-SEM). A gas sensor was constructed with the prepared Zn 2 SnO 4 nanospheres and used to detect ethanol gas and some other gases. Because of the special nanostructure and a relative large specific surface area (45.5 m 2 /g), the Zn 2 SnO 4 -based sensor showed a remarkable gas-sensing performance, including low operating temperature (180 °C), high response (23.4–50 ppm ethanol gas), fast response–recovery time and excellent selectivity to ethanol gas, which suggested the promising application of the Zn 2 SnO 4 nanomaterials.

A “cobalt-free” double perovskite electrode material with stoichiometric composition Sr 2 FeTiO 6− δ (SFT) has been developed for intermediate-temperature solid oxide fuel cells (IT-SOFCs) using Ce 0.8 Sm 0.2 O 1.9 (SDC) electrolyte. The reactivity tests show that the SFT electrode is chemically compatible with the SDC electrolyte at 1100 °C for 10 h. The electrical conductivity of SFT sample reaches 2.83–2.33 S cm −1 the temperature range of 600–800 °C. The thermal expansion coefficient of the SFT sample is 16.8×10 −6 K −1 the temperature range of 30–1000 °C in air, which is lower than that of most of the reported Co-based electrodes. Using NiO–SDC as anode, SFT as cathode, and SDC as supported electrolyte, the single cell exhibits maximum power density of 441 mW cm −2 at 800 °C. The area specific resistances of the SFT electrode on SDC electrolyte calcined at 1000 °C were found to be 0.051, 0.094 and 0.204 Ω cm 2 at 800, 750 and 700 °C, respectively. Maximum power density of 335 mW cm −2 has been achieved for a symmetrical single cell with the configuration of SFT/SDC/SFT at 800 °C with wet H 2 as fuel and ambient air as oxidant. These results indicate that SFT is a very promising electrode candidate for IT-SOFCs with SDC electrolyte.

Er- and Zr-codoped strontium bismuth niobate ceramics, Sr 0.97 Er 0.03 Bi 2 Nb 2− x Zr x O 9 (SBN x ) with different x (0≤ x ≤0.1), were synthesized by the solid state reaction method. Their structural, up-conversion (UC) photoluminescence, and dielectric properties were investigated. By Rietveld structural refinement, all SBN x samples exhibited a polycrystalline bismuth-layered perovskite structure with space group A2 1 am. With deliberate introduction of Zr 4+ ions in the bismuth-layered perovskite structure, SBN x samples presented simultaneously enhanced UC photoluminescence and dielectric properties. The UC photoluminescence was investigated as a function of Zr 4+ concentration and incident pump power. Under the 980 nm near infrared (NIR) excitation, bright UC green and weak red emissions were observed which corresponded to the transitions from 2 H 11/2 / 4 S 3/2 and 4 F 9/2 to 4 I 15/2 level, respectively. With x increase, the UC luminescence improvement of SBN x can be attributed to the local distortion of crystal field surrounding the Er 3+ activator which induced by different ionic radii of Zr 4+ and Nb 5+ ions. The dependence of UC emission intensity on pumping power showed that two photon energy transfer process was involved in the UC green and red emissions. Furthermore, electrical measurements indicated that the introduction of Zr 4+ distinctly increased the ferroelectric to paraelectric phase transition temperature ( T C ) of SBN x ceramics from 724 K to 762 K as x ranging from 0.0 to 0.1. It is believed that B site doping in SBN x by large Zr 4+ ion is an effective method to improve UC luminescence and electrical properties of this potentially multifunctional optical-electro material.

Er 3+ -doped filled tungsten bronze Ba 6 Ti 2 Nb 8 O 30 –Sr 6 Ti 2 Nb 8 O 30 solid solutions with different Ba 6 Ti 2 Nb 8 O 30 /Sr 6 Ti 2 Nb 8 O 30 ratios (SBTN x ) have been prepared by a high temperature solid-state reaction. The crystal structure has been investigated simultaneously by the Rietveld structural refinement and upconversion photoluminescence (UC-PL) spectra. It is found that the crystal structure of SBTN x changes from TE-FTB symmetry (0≤ x ≤3, space group P4bm) to OR-FTB symmetry (3.5≤ x ≤5.91, space group Pba2) with x increasing. More interestingly, the structure transition of SBTN x system is also revealed by the UC-PL spectra which indicate the intimate correlation between the UC-PL spectra and the structure transition. Furthermore, the underlying origin concerning the variation of UC-PL spectra has been studied from crystal structure aspect which suggests UC-PL spectra can be explored as a structure probe for present filled tungsten bronze solid solutions.

Ba4La1−xSmxTiNb9O30 (BLTN: Sm3+x) ceramics with different x have been synthesized. Their structural, photoluminescence, dielectric, and ferroelectric properties are investigated. By Rietveld structural refinement, BLTN: Eu3+x samples belong to the single unfilled tetragonal tungsten bronze (TTB) phase with space group P4bm. With deliberate introduction of Sm3+ ions in the unfilled TTB-type structure, BLTN: Sm3+x samples simultaneously present bright reddish-orange emission and enhanced electrical properties. The reddish-orange emission, originating from 4G5/2→6HJ (J=5/2, 7/2, and 9/2) transitions, has been observed by naked eyes under near ultraviolet radiation at room temperature. Furthermore, dielectric permittivity sharply changes with x and finally ferroelectric phase transitions above room temperature are realized in BLTN: Sm3+x under the stimulation of Sm3+ ions. It is believed that BLTN: Sm3+x involving bright reddish-orange emission and enhanced electrical properties may act as a potentially multifunctional optical-electro material.

Layered cobalt oxide materials YBaCo3.4Al0.3Ga0.3O7+δ (YBCAG33) and YBaCo3.2Al0.4Ga0.4O7+δ (YBCAG44) were prepared and the electrical conductivity, the thermal expansion coefficient and electrochemical performance were investigated as potential cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs). The highest conductivity of 6.2 S cm−1 is found for YBCAG33 at 900 °C in air. The average thermal expansion coefficients of YBCAG33 and YBCAG44 in the range of 30–850 °C are 9.3×10−6 K−1 and 9.0×10−6 K−1, respectively. The ASR value of YBCAG33 and YBCAG44 cathodes on LSGM electrolyte is as low as 0.080 Ω cm2 and 0.120 Ω cm2 at 800 °C, respectively. In an electrolyte-supported single test cell, the YBCAG33 cathode exhibited maximum power densities of 392, 292, 203, and 129 mW cm−2 at 800, 750, 700, and 650 °C, respectively. Preliminary results demonstrated that the YBCAG33 can be a promising alternative cathode materials in IT-SOFCs in terms of electrochemical performance.

Sm 3+ ions doped Bi 1/2 Na 1/2 TiO 3 (BNTO: x Sm 3+ ) polycrystalline samples with different Sm 3+ concentrations were synthesized through the solid-state reaction method. Their microstructural, photoluminescence, and ferroelectric (FE) properties were investigated. Strong reddish-orange emission centered at 597 nm has been successfully observed at room temperature. More importantly, the strong emission of BNTO: x Sm 3+ can be excited by both blue light and near ultraviolet radiation which indicates that BNTO: x Sm 3+ can act as a potential phosphor. Furthermore, the optimized photoluminescence is realized in BNTO: x Sm 3+ with x =0.02 sample which also shows relatively good ferroelectric properties.

A series of polycrystalline Bi 4− x Ho x Ti 3 O 12 (BiT: x Ho 3+ ) ( x =0.0, 0.01, 0.03, 0.05, 0.1, 0.15, 0.2, 0.3, and 0.4) samples were synthesized through the solid-state reaction method, and their microstructural, photoluminescence, ferroelectric (FE), and dielectric properties were investigated. Under the excitation of 455 nm light, the sample exhibits a strong green emission peak centered at 545 nm which corresponds to the transition from 5 S 2 to 5 I 8 . The optimal emission intensity was obtained when x =0.05 for the BiT: x Ho 3+ system. More importantly, enhanced ferroelectric and dielectric properties were also obtained with Ho doping.

The GdBaCuCo 0.5 Fe 0.5 O 5+ δ (GBCCF) layered perovskite oxide was evaluated as novel cathode for intermediate temperature solid oxide fuel cells (IT-SOFCs). Its electrical conductivity was 9–13 S cm −1 at 650–800 °C in air. The average thermal expansion coefficient (TEC) of GBCCF was 14.4 × 10 −6 K −1 , which was close to that of the typical electrolyte material. The cathode polarization resistance of GBCCF was 0.650 Ω cm 2 at 750 °C and it decreases to 0.118 Ω cm 2 when Ce 0.9 Gd 0.1 O 1.95 (GDC) was added to form a GBCCF–GDC composite cathode. Preliminary results indicated that layered perovskite GBCCF was a promising alternative cathode material for IT-SOFCs.

The performance of the LaBaCuFeO 5+ δ –Ce 0.8 Sm 0.2 O 1.9 (LBCF–SDC) composite cathodes was studied in this paper. Electrical conductivity, thermal expansion and electrochemical properties were investigated by four probing DC technique, dilatometry, AC impedance and polarization techniques, respectively. The thermal expansion coefficients of the LBCF–SDC were between (16.3 and 13.4) × 10 −6 K −1 from 30 to 850 °C, which was lower value than LBCF (17.0 × 10 −6 K −1 ). AC Impedance spectroscopy measurements of LBCF–SDC/SDC/LBCF–SDC test cell were carried out. Polarization resistance values for the LBCF–SDC10 cathode was as low as 0.097 Ω cm 2 at 750 °C.