Piezoelectric materials that can function at high temperatures without failure are desired for structural health monitoring and/or nondestructive evaluation of the next generation turbines, more efficient jet engines, steam, and nuclear/electrical power plants. The operational temperature range of smart transducers is limited by the sensing capability of the piezoelectric material at elevated temperatures, increased conductivity and mechanical attenuation, variation of the piezoelectric properties with temperature. This article discusses properties relevant to sensor applications, including piezoelectric materials that are commercially available and those that are under development. Compared to ferroelectric polycrystalline materials, piezoelectric single crystals avoid domain-related aging behavior, while possessing high electrical resistivities and low losses, with excellent thermal property stability. Of particular interest is oxyborate [ReCa4O (BO3)3] single crystals for ultrahigh temperature applications (>1000°C). These crystals offer piezoelectric coefficients deff, and electromechanical coupling factors keff, on the order of 3–16 pC/N and 6%–31%, respectively, significantly higher than those values of α-quartz piezocrystals (~2 pC/N and 8%). Furthermore, the absence of phase transitions prior to their melting points ~1500°C, together with ultrahigh electrical resistivities (>106 Ω·cm at 1000°C) and thermal stability of piezoelectric properties (< 20% variations in the range of room temperature ~1000°C), allow potential operation at extreme temperature and harsh environments.

Piezoelectric Materials for High Temperature Sensors

Cobalt spinel oxides are a class of promising transition metal (TM) oxides for catalyzing oxygen evolution reaction (OER). Their catalytic activity depends on the electronic structure. In a spinel oxide lattice, each oxygen anion is shared amongst its four nearest transition metal cations, of which one is located within the tetrahedral interstices and the remaining three cations are in the octahedral interstices. This work uncovered the influence of oxygen anion charge distribution on the electronic structure of the redox-active building block Co-O. The charge of oxygen anion tends to shift toward the octahedral-occupied Co instead of tetrahedral-occupied Co, which hence produces strong orbital interaction between octahedral Co and O. Thus, the OER activity can be promoted by pushing more Co into the octahedral site or shifting the oxygen charge towards the redox-active metal center in CoO6 octahedra.

Shifting Oxygen Charge Towards Octahedral Metal: A Way to Promote Water Oxidation on Cobalt Spinel Oxides

Luminescent semiconductor quantum dots (QDs) are a new class of fluorescent label with wide-ranging applications for cell imaging. The electron density and elemental composition of these materials permit the extension of their use as probes in conventional electron microscopy (TEM) and energy-filtered TEM (EFTEM). Here we illustrate the feasibility of using streptavidin-conjugated QDs as TEM tags by labeling a nuclear protein on cell sections and obtaining correlative fluorescence and TEM data. We also show that QD probes can be employed in conjunction with immunogold for co-localization of proteins at the ultrastructural level. Furthermore, by obtaining cadmium elemental maps of CdSe/ZnS QDs distributed on a nuclear structure, we demonstrate the potential of QDs for co-localization of multiple proteins when used in combination with EFTEM.

Application of Quantum Dots as Probes for Correlative Fluorescence, Conventional, and Energy-filtered Transmission Electron Microscopy

Nickel Spinel Ferrites: A review

Blue pigments based on CoxZn1−xAl2O4 spinels synthesized by the polymeric precursor method

Synthesis, structure and optical properties of CoAl2O4 spinel nanocrystals

CoxZn1–xAl2O4 (x = 0.01–0.6) nanoparticles were synthesized by the citrate sol–gel method and were characterized by X-ray powder diffraction and transmission electron microscopy to identify the crystalline phase and determine the particle size. X-ray photoelectron spectroscopy and 27Al solid-state NMR spectroscopy were used to study the distribution of the cations in the tetrahedral and octahedral sites in CoxZn1–xAl2O4 nanoparticles as a function of particle size and composition. The results show that all of the as-synthesized samples exhibit spinel-type single phase; the crystallite size of the samples is about 20–50 nm and increases with increasing annealing temperature and decreases with Co-enrichment. Zn2+ ions are located in large proportions in the tetrahedral sites and in small proportions in the octahedral sites in CoxZn1–xAl2O4 nanoparticles. The fraction of octahedral Zn2+ increases with increasing Co concentration and decreases with increasing particle size. Besides the tetrahedral and octahed...

Cation distribution in co-doped ZnAl2O4 nanoparticles studied by X-ray photoelectron spectroscopy and 27Al solid-state NMR spectroscopy.

Preparation of Co2+-doped ZnAl2O4 nanoparticles by citrate sol–gel method

Spectroscopic properties of Co2+: ZnAl2O4 nanocrystals in sol–gel derived glass–ceramics

Cadmium mercury thiocyanate (CdHg(SCN) 4 , CMTC) and its two lewis base adducts: cadmium mercury thiocyanate dimethyl-sulphoxide (CdHg(SCN) 4 (H 6 C 2 OS) 2 , CMTD) and cadmium mercury thiocyanate glycol monomethyl ether (CdHg(SCN) 4 (C 3 H 8 O 2 ), CMTG) have been discovered as nonlinear optical (NLO) crystal materials. Their structural, optical and physicochemical properties were characterized by X-ray powder diffraction (XRPD), infrared spectroscopy, vis/UV/NIR spectra and thermal analysis. It is discovered that their transparency cutoffs lie in the UV region and CMTD crystals possess the shortest cutoff wavelength among the three crystal materials.

Xiulan Duan

Papers

Synthesis, structure and optical properties of CoAl2O4 spinel nanocrystals

Cation distribution in co-doped ZnAl2O4 nanoparticles studied by X-ray photoelectron spectroscopy and 27Al solid-state NMR spectroscopy.

Preparation of Co2+-doped ZnAl2O4 nanoparticles by citrate sol–gel method

Spectroscopic properties of Co2+: ZnAl2O4 nanocrystals in sol–gel derived glass–ceramics

Preparation and Characterization of Nonlinear Optical Crystal Materials: Cadmium Mercury Thiocyanate and its Lewis Base Adducts