Sun Hualei, Woodruff Daniel N, Cassidy Simon J, Allcroft Genevieve M, Sedlmaier Stefan J, Thompson Amber L, Bingham Paul A, Forder Susan D, Cartenet Simon, Mary Nicolas, Ramos Silvia, Foronda Francesca R, Williams Benjamin H, Li Xiaodong, Blundell Stephen J, Clarke Simon J
Department of Chemistry, Inorganic Chemistry Laboratory, University of Oxford , South Parks Road, Oxford, OX1 3QR, U.K.
Inorg Chem. 2015 Feb 16;54(4):1958-64. doi: 10.1021/ic5028702. Epub 2015 Jan 23.
Hydrothermal synthesis is described of layered lithium iron selenide hydroxides Li(1-x)Fe(x)(OH)Fe(1-y)Se (x ∼ 0.2; 0.02 < y < 0.15) with a wide range of iron site vacancy concentrations in the iron selenide layers. This iron vacancy concentration is revealed as the only significant compositional variable and as the key parameter controlling the crystal structure and the electronic properties. Single crystal X-ray diffraction, neutron powder diffraction, and X-ray absorption spectroscopy measurements are used to demonstrate that superconductivity at temperatures as high as 40 K is observed in the hydrothermally synthesized samples when the iron vacancy concentration is low (y < 0.05) and when the iron oxidation state is reduced slightly below +2, while samples with a higher vacancy concentration and a correspondingly higher iron oxidation state are not superconducting. The importance of combining a low iron oxidation state with a low vacancy concentration in the iron selenide layers is emphasized by the demonstration that reductive postsynthetic lithiation of the samples turns on superconductivity with critical temperatures exceeding 40 K by displacing iron atoms from the Li(1-x)Fe(x)(OH) reservoir layer to fill vacancies in the selenide layer.
描述了水热合成层状氢氧化锂铁硒化物Li(1-x)Fe(x)(OH)Fe(1-y)Se（x ∼ 0.2；0.02 < y < 0.15）的过程，该化合物在硒化铁层中具有广泛的铁位点空位浓度范围。这种铁空位浓度被揭示为唯一显著的成分变量以及控制晶体结构和电子性质的关键参数。使用单晶X射线衍射、中子粉末衍射和X射线吸收光谱测量来证明，当铁空位浓度较低（y < 0.05）且铁氧化态略低于 +2时，在水热合成的样品中观察到高达40 K的超导性，而具有较高空位浓度和相应较高铁氧化态的样品则不超导。通过证明样品的还原后合成锂化通过将铁原子从Li(1-x)Fe(x)(OH)储层层中置换出来以填充硒化物层中的空位，从而开启临界温度超过40 K的超导性，强调了在硒化铁层中将低铁氧化态与低空位浓度相结合的重要性。
