- Synthesis and Transport Properties of the Family of Zintl Phases Ca3RESb3(RE = La-Nd, Sm, Gd-Tm, Lu): Exploring the Roles of Crystallographic Disorder and Core 4f Electrons for Enhancing Thermoelectric Performance
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Zintl phases with complex crystal structures have been studied as promising candidate materials for thermoelectric (TE) applications. Here, we report the syntheses of the family of rare-earth metal Zintl phases with the general formula Ca4-xRExSb3 (x ≈ 1; RE = La-Nd, Sm, Gd-Tm, Lu). The structural elucidation is based on refinements of single-crystal X-ray diffraction data for 12 unique chemical compositions. The cubic structure is confirmed as belonging to the anti-Th3P4 structure type (space group I4ˉ 3d, no. 220, Z = 4), where the Ca and RE atoms share the same atomic site with ca. 75 and 25% occupancies, respectively. Such crystallographic disordering of divalent Ca and trivalent RE atoms in the structure provides a pathway to intricate bonding. The latter, together with the presence of heavy elements such as Sb and the lanthanides, are expected to enhance the scattering probability of phonons, thereby leading to low thermal conductivity κ comparable to that of the ordered RE4Sb3. The drive of the hypothetical parent compound Ca4Sb3 to be stabilized by alloying with rare-earth metals can be understood following the Zintl-Klemm concept, as the resultant formula may be rationalized as (Ca2+)3RE3+(Sb3-)3, indicating the realization of closed-shell electronic configurations for all elements. This notion is confirmed by electronic structure calculations, which reveal narrow bandgaps Eg = 0.77 and 0.53 eV for Ca3LaSb3 and Ca3LuSb3, respectively. In addition, the incorporation of RE atoms into the structure drives the phase into a state of a degenerate semiconductor with dominant hole charge carriers.
- Ogunbunmi, Michael O.,Baranets, Sviatoslav,Bobev, Svilen
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p. 9382 - 9392
(2021/12/13)
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- New ternary La2Sb-type compounds, ScRESb (RE = La, Ce, Pr, Nd, Sm, Tb), and the oxygen stuffed variant Sc4Yb4Sb 4O
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Scandium rare-earth metal antimonides, ScRESb (RE = La, Ce, Pr, Nd, Sm, Tb) were synthesized from scandium metal and binary RESb at 1770 K in tantalum ampoules. According to X-ray analyses of the crystal structures, they adopt the tetragonal ScCeSi-type of structure (space group I4/mmm, Pearson code tI12), a variant of La2Sb, with a fully ordered atom distribution. Especially in ScSmSb and ScTbSb, the scandium atoms are distorted from an ideal 4 4 net in a way to form Sc nets of squares and rhombi in order to adjust to the lattice shrinkage in the ab plane, caused by the lanthanide contraction. Finally the structure changes from La2Sb to Sc 2Sb-type (anti-PbFCl-type), when terbium is replaced by dysprosium. The respective compound with ytterbium was only found when stoichiometric amounts of oxygen were present, resulting in Sc4Yb4Sb 4O, a La2Sb-type variant stuffed with oxygen. A structure field map, based on specific geometric parameters, easily allows for distinguishing between oxygen stuffed and oxygen-free compounds. Magnetic susceptibility measurements of ScCeSb, ScPrSb, and ScNdSb indicate Curie-Weiss behavior with ferromagnetic exchange coupling underlying. The magnetic moments correspond to the expected values for RE3+. Copyright
- Nuss, Juergen,Jansen, Martin
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p. 713 - 718
(2014/04/17)
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- Structural and 121Sb M?ssbauer spectroscopic investigations of the antimonide oxides REMnSbO (RE = La, Ce, Pr, Nd, Sm, Gd, Tb) and REZnSbO (RE = La, Ce, Pr)
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Quaternary antimonide oxides REMnSbO (RE = La, Ce, Pr, Nd, Sm, Gd, Tb) and REZnSbO (RE = La, Ce, Pr) were synthesized from the RESb monoantimonides and MnO, respectively ZnO, in sealed tubes at 1170 K. Single crystals were obtained from NaCl/KCl salt fluxes. The ZrCuSiAs-type (space group P4/nmm) structures of LaMnSbO (a = 423.95(7), c = 955.5(27) pm, wR2 = 0.067, 247 F2), CeMnSbO (a = 420.8(1), c = 950.7(1) pm, wR2 = 0.097, 250 F2), SmMnSbO (a = 413.1(1), c = 942.3(1) pm, wR2 = 0.068, 330 F2), LaZnSbO (a = 422.67(6), c = 953.8(2) pm, wR2 = 0.052, 259 F2), and NdZnSbO (a = 415.9(1), c = 945.4(4) pm, wR2 = 0.109, 206 F2) were refined from single crystal X-ray diffractometer data. The structures consist of covalently bonded (RE3+O2-)+ and (T2+Sb 3-)- layers with weak ionic interlayer interactions. The oxygen and transition metal atoms both have tetrahedral coordination within the layers. 121Sb Mossbauer spectra of the REMnSbO and REZnSbO compounds show single antimony sites with isomer shifts close to -8 mms-1, in agreement with the antimonide character of these compounds. PrMnSbO and NdMnSbO show transferred hyperfine fields of 8 T at 4.2 K.
- Schellenberg, Inga,Nilges, Tom,P?ttgen, Rainer
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p. 834 - 840
(2009/03/11)
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- Pressure-induced phase transitions in lanthanide monoantimonides with a NaCl-type structure
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By use of synchrotron radiation the powder x-ray diffraction of LnSb (Ln=lanthanide) with a NaCl-type structure has systematically been studied up to 40 GPa at room temperature. First-order phase transitions with the crystallographic change occur for LnSb at high pressures. The structure of the high-pressure phases of LnSb is classified into three groups. The lighter LnSb (Ln=La, Ce, Pr, and Nd) have the tetragonal structure (distorted CsCl-type) at high pressures. The high-pressure form of the middle LnSb (Ln=Sm, Gd, and Tb) is unknown. The heavier LnSb (Ln=Dy, Ho, Er, Tm, and Lu) show the typical NaCl-CsCl (B1-B2) transition at high pressures though the same transition is not observed in the heavier LnP and LnAs. The transition pressures of LnSb increase with decreasing lattice constant in the NaCl-type structure and do not depend on the structure of their high-pressure phases. The high-pressure structural behavior of LnSb is discussed.
- Shirotani, Ichimin,Hayashi, Junichi,Yamanashi, Keigo,Ishimatsu, Naoki,Shimomura, Osamu,Kikegawa, Takumi
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- Phase transitions of LnSb (Ln = lanthanide) with NaCl-type structure at high pressures
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Using synchrotron radiation, X-ray diffraction patterns of LnSb (Ln = Pr, Nd, Sm, Gd and Tb) with a NaCl-type structure have been measured up to 30 GPa at room temperature. First-order phase transitions with a crystallographic change occur at around 13 GPa for PrSb and 15 GPa for NdSb. The structure of the high-pressure phases of both antimonides is tetragonal (Ln: 0,0,0; Sb: 1/2, 1/2, 1/2; space group P4/mmm), and can be viewed as a distorted CsCl structure. The structure of the high-pressure phase of LnSb (Ln = La, Ce, Pr and Nd) is more anisotropic compared with that of corresponding LnP. Pressure-induced phase transitions of SmSb, GdSb and TbSb are observed at around 19, 22 and 21 GPa, respectively.
- Hayashi,Shirotani,Tanaka,Adachi,Shimomura,Kikegawa
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p. 561 - 565
(2008/10/08)
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- 121Sb MOESSBAUER INVESTIGATION OF THE RARE EARTH ANTIMONIDES.
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**1**2**1Sb Moessbauer spectra have been obtained for the series R Sb (R equals La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, and Yb) at 78 K and for a selection of the compounds at 5. 5 K. At 78 K all the spectra show a single line. The isomer shifts are close to that of InSb and show a linear increase with increasing atomic number of the rare earth ion. Many of the rare earth antimonides exhibit a variety of magnetic and structural phase transitions at a sufficiently low temperature. Spectra obtained at 5. 5 K are interpreted in terms of these phase transitions.
- Holbourn,Woodhams
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p. 186 - 194
(2008/10/09)
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