Five novel Zintl phases belonging to the ternary Ca11–x RE x Sb10–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 Sb4 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.
Five ternary and quaternary Zintl phases in the solidsolution Ca 11−x A x Sb 10−y Ge z (A = Na, Li; 0.06(3) ≤ x ≤ 0.17(5), 0.19(1) ≤ y ≤ 0.55(1), 0.13(1) ≤ z ≤ 0.22(1)) system have been successfully synthesized by both of the arc-melting and the molten Pb metal-flux reactions. The crystal structure of these title compounds was characterized by powder and single-crystal X-ray diffractions analyses, and all title compounds crystallized in the Ho 11 Ge 10 -type phase in the tetragonal space group I4/mmm (Z = 4, Pearson code tI84). The complex crystal structure can be described as an assembly of 1) three kinds of cationic polyhedra centered by three different Sb and 2) the cage-shaped anionic frameworks built through the connection of two types of Sb. The newly substituted p-type double dopants of the cationic (Na and Li) and anionic (Ge) elements displayed particular site preferences, which were successfully explained by either the size-factor criterion based on the atomic size or the electronic-factor criterion based on the electronegativity of an element. Quite interestingly, as the reaction conditions were changed, the morphology shift of single crystals in Ca 10.94(3) Na 0.06 Sb 9.58(1) Ge 0.21 occurred from a cubic-shaped to a hummocky-type, to a hopper-type, and eventually to an octahedral-shaped crystal, just like the Yakutian kimberlite diamonds. Moreover, we firmly believe that the inclusion of the p-type Ge dopant for Sb was crucial to trigger this type of morphology shift and complete the octahedral-shaped morphology in the overall crystal-growth mechanism. The theoretical calculations using a DFT method rationalized the observed site preference of Na and the electronic effect of the p-type Ge dopants. The Seebeck coefficient measurements for Ca 10.88(4) Li 0.12 Sb 9.45(1) Ge 0.21 indicated that some portions of electron charge carriers were effectively eliminated by the p-type double dopants using Li and Ge.
Three novel Zintl phase solid-solutions in the Ca11-xGdxSb10-y (0.36(2) ≤ x ≤ 0.58(4), 0.26(1) ≤ y ≤ 0.37(1)) system have been successfully synthesized by arc-melting, and their crystal structures were...
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