Site-Selective n-Type "Heavy" Rare-Earth-Metal Doping in the Complex Zintl Phase Ca11-xRExSb10-y (RE = Tb, Dy, Ho, Er, Tm)

초록

Five novel Zintl phases belonging to the ternary Ca11-xRExSb10-y (RE = Tb, Dy, Ho, Er, Tm; 0.35(6) <= x <= 0.41(4), 0.27(1) <= y <= 0.51(2)) system were successfully synthesized by the arc-melting method, and their crystal structures were carefully determined by using powder and single-crystal X-ray diffraction (PXRD and SXRD) analyses. Large amounts of nicely grown plate-shaped single crystals were easily obtained using this relatively facile synthetic method, and all title compounds adopted the tetragonal I4/mmm space group with Z = 4 and a Pearson code of tI84. This isotypic Ho11Ge10-type structure of the title compounds can be illustrated as a combination of (1) three different types of cationic coordination polyhedra centered by three isolated Sb atoms and (2) three-dimensional (3D) anionic frameworks formed by two different types of Sb atoms. These ternary compounds successfully accommodated the n-type RE3+ dopants at the Ca2 (Wyckoff 16n) site of the parental binary Ca11Sb10, and this particular site preference can be elucidated by the substituting cationic size and the volume of the provided cationic site. A series of theoretical calculations were also performed using the hypothetical model Ca10.5Ho0.5Sb10 by the tight-binding linear muffin-tin orbital (TB-LMTO) method. Thorough analyses of crystal orbital Hamilton population (COHP) curves proved that the antibonding character of the Sb3-Sb3 bond induced the observed deficiencies of the square Sb-4 sites. Magnetic property measurements performed for three title compounds, Ca10.59(4)Dy0.41Sb9.71(1), Ca10.61(3)Ho0.39Sb9.69(1), and Ca10.64(3)Er0.36Sb9.73(1), indicated the antiferromagnetic (AFM) interactions of RE elements at relatively low temperatures with paramagnetic Curie temperatures of -2.24, -2.80, and -2.98 K, respectively.

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