|
Résumé |
In solid state chemistry, conventional high-temperature reaction limits the control of structures of nonmolecular compounds to only those usually obtainable within the bounds of known structural types like spinels, perovskites and pyrochlores. Reactions at low temperatures may erase this boundary, opening a door to obtain unprecedented structures as metastable phases. Furthermore, when such reactions proceed topotactically, i.e., the basic framework is kept between structures before and after the reaction, we (inorganic chemists) are able to rationally construct or design structures, just as organic chemists usually do. In my talk, I will demonstrate two synthetic strategies that can be then used for study of low-dimensional magnetism. The first is low-temperature ion-exchange reaction of layered perovskites to produce a series of S = 1/2 square-lattice antiferromagnets, (CuX)An-1BnO3n+1 (A = Sr, La…; B = Nb, Ta; X = Cl, Br; n = 2,3…). Depending on the choice of A, B, X, and n, we observed various quantum phenomena ranging from a spin-liquid state with a gap in (CuCl)LaNb2O7,a stripe order in (CuBr)LaNb2O7,and to a 1/3 magnetization plateau in (CuBr)Sr2Nb3O10.The second is low-temperature reducing reaction of SrFeO3 to produce SrFeO2 with an unusual square-planar coordination around iron. It is isostructural with an “infinite-layer compound” SrCuO2. Most likely reflecting the unusual coordination, the in-plane Fe-O bonds are extremely of covalent nature and give a magnetic order far above room temperature in spite of the 2D structure. |
