Preparation of LaTiO2N Using Hydrothermally Synthesized La2Ti2O7 as a Precursor and Urea as a Nitriding Agent

A facile method was successfully developed to prepare perovskite‐type metal oxynitrides, LaTiO2N, from La2Ti2O7 as a precursor in an atmosphere of N2. Urea was employed as a solid‐state nitriding agent, instead of gaseous NH3, to increase the safety of the reaction. The hydrothermally prepared La2Ti2O7 precursor had a nanosheet morphology and contained La(OH)3 as a by‐product. Through the optimization of reaction conditions including heat‐treatment temperature and content of urea, single‐phase LaTiO2N could be obtained. In addition, we revealed that the La(OH)3 present in the La2Ti2O7 precursor played an important role in the nitriding process using urea. La2O2CN2 was generated by the reaction of La(OH)3 with the thermal decomposition products of urea at the medium temperature range. This indicated that the NH3 gas released from the thermal decomposition of urea did not directly cause nitridation of the La2Ti2O7 precursor.This work was supported by JSPS KAKENHI Grant Numbers JP16H06439, JP17H05483, and JP17H03392. This work was partly supported by the Center for Functional Nano Oxide at Hiroshima University.アクセプト後にキーワードの変更あり

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements