Phase transformations in multicomponent rare earth sesquioxides were studied by splat quenching from the melt, high-temperature differential thermal analysis and synchrotron X-ray diffraction on laser-heated samples. Three compositions were prepared by the solution combustion method: (La,Sm,Dy,Er,RE)2O3, where all oxides are in equimolar ratios and RE is Nd or Gd or Y. After annealing at 800 °C, all powders contained mainly a phase of C-type bixbyite structure. After laser melting, all samples were quenched in a single-phase monoclinic B-type structure. Thermal analysis indicated three reversible phase transitions in the range 1900–2400 °C, assigned as transformations into A, H, and X rare earth sesquioxides structure types. Unit cell volumes and volume changes on C-B, B-A, and H-X transformations were measured by X-ray diffraction and consistent with the trend in pure rare earth sesquioxides. The formation of single-phase solid solutions was predicted by Calphad calculations. The melting point was determined for the (La,Sm,Dy,Er,Nd)2O3 sample as 2456 ± 12 °C, which is higher than for any of constituent oxides. An increase in melting temperature is probably related to nonideal mixing in the solid and/or the melt and prompts future investigation of the liquidus surface in Sm2O3-Dy2O3, Sm2O3-Er2O3, and Dy2O3-Er2O3 systems.

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The BaO–Sm2O3 system is of interest for the optimization of synthesis of electroceramics. The only systematic experimental study of phase equilibria in the system was performed more than 40 years ago. The reported experimental values of the enthalpy of formation of BaSm2O4 are in conflict, and the reported compound Ba3Sm4O9 has never been confirmed. In this work we synthesized BaSm2O4 by solid‐state reaction and determined its heat capacity, enthalpy of formation, and phase transitions by differential scanning calorimetry, high‐temperature oxide melt solution calorimetry and ultra‐high‐temperature differential thermal analysis, respectively. We confirmed the existence of Ba3Sm4O9 and its apparent stability from 1873 to 2273 K by X‐ray diffraction on quenched laser‐melted samples but were not able to obtain single‐phase material for calorimetric measurements. The CALPHAD method was used to assess phase equilibria in the BaO–Sm2O3 system, using both available literature data and our new measurements. A self‐consistent thermodynamic database and the calculated phase diagram of the BaO–Sm2O3 system are provided. This work can be used to model and thus to understand the relationships among composition, temperature, and microstructure for multicomponent systems with BaO and Sm2O3.

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As an important parameter of HIPIMS, pulse frequency has significant influence on the microstructure and mechanical properties of the deposited coatings, especially for the multi-component coatings deposited by using a spliced target with different metal sputtering yields. In this study, a single Al67Ti33-V-Cu spliced target was designed to prepare Al-Ti-V-Cu-N coatings by using high power impulse magnetron sputtering (HIPIMS). The results showed that the peak target current density decreased from 0.75 to 0.24 A•cm −2 as the pulse frequency increased, along with the microstructure transferred from dense structure to coarse column structure. The pulse frequency has significant influence on chemical compositions of Al-Ti-V-Cu-N coatings, especially for Cu content increasing from 6.2 to 11.7 at.%. All the coatings exhibited a single solid-solution phase of Ti-Al-V-N, and the preferred orientation changed from (111) to (220) when the pulse frequency increased above 200 Hz. The decrease in peak target current density at high pulse frequencies resulted in a sharp decrease in the coating hardness from 35.2 to 16.4 GPa, whereas the relaxation of compressive residual stress contributed to an improvement in adhesion strength from 43.3 to 79.6 N.

Introducing the density of states or defects within the band gap in two-dimensional nanomaterials by rare-earth (RE) element substitution would make them potential candidates for application in next-generation optoelectronic devices. Furthermore, doping with RE elements possessing fine-structured spectral emission and absorption can improve the fundamental research and technological applications of two-dimensional nanomaterial-based photoelectrochemical (PEC) activity due to abundant active sites and low interfacial contact resistance with the electrolyte. Herein, an Er-doping strategy is utilized for the synthesis of Er-doped WS 2 nanosheets to simultaneously achieve both upconversion and downconversion emissions, which can efficiently absorb more solar light for PEC activity. We first report a two-step method combining magnetic sputtering and sulfurization to synthesize Er-doped WS 2 nanosheet-based electrodes. The effect of Er doping into a single-phase hexagonal-structured WS 2 (p-type semiconductor)based electrode on PEC activity is investigated and compared with pristine WS 2 counterparts under one standard sun condition. Results indicate that a photocurrent density of −20 μA•cm −2 at −0.21 V versus RHE (reversible hydrogen electrode) with an enhancement factor of ∼200-fold due to a wider absorbance range (400−808 nm) and a decreased overpotential for hydrogen reduction are achieved. Moreover, the resistance of the Er-doped WS 2 electrode is found to be decreased from 500 to 28 kΩ, with nearly a 20-fold decrease compared with that of the pristine WS 2 counterparts, contributing to the higher efficiency in electron transfer into the electrolyte. The mechanism is confirmed by Monte Carlo simulations and first-principles calculations. The Er-doped WS 2 nanosheets are therefore a promising substitute for noble metals in PEC applications.

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