Article

Synthesis and properties of CaCd 2Sb 2 and EuCd 2Sb 2

Intermetallics (Impact Factor: 2.12). 01/2010; 18(1):193-198. DOI: 10.1016/j.intermet.2009.07.011

ABSTRACT High density polycrystalline CaCd2Sb2 and EuCd2Sb2 intermetallics are synthesized by Spark Plasma Sintering and their thermoelectric properties are investigated. X-ray diffraction measurements reveal both materials have a structure in R3¯m space group, containing a small amount of CdSb as a second phase. Thermoelectric measurements indicate both are p-type conductive materials. The figure of merit value of CaCd2Sb2 is 0.04 at 600K and that of EuCd2Sb2 is 0.60 at 617K. Theoretical calculations show that CaCd2Sb2 is a degenerate semiconductor with a band gap of 0.63eV, while EuCd2Sb2 is metallic with DOS of 13.02electrons/eV. For deeper understanding of the better thermoelectric properties of EuCd2Sb2, its low temperature magnetic, transport and heat capacity properties are investigated. Its Nèel temperature is 7.22K, convinced by heat capacity anomaly at 7.13K. Hall effect convinced that it is a p-type conductive material. It has high Hall coefficient, high carrier concentration and high carrier mobility of +1.426cm3/C, 4.38×1018/cm3 and 182.40cm2/Vs, respectively. They are all in the magnitude of good thermoelectric materials. The Eu 4f level around Fermi energy and antiferromagnetic order may count for the better thermoelectric properties of EuCd2Sb2 than that of CaCd2Sb2.

1 Follower
 · 
87 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Two series of Mn-substituted rare-earth zinc arsenides RE1-yMnxZn2-xAs2 (RE = Eu-Lu) and RE2-yMnxZn4-xAs4 (RE = La-Nd, Sm, Gd) were prepared by reaction of the elements at 750 °C. Both series are derived from ideal empirical formula REM2As2 (M = Mn, Zn) and adopt crystal structures related to the trigonal CaAl2Si2-type (space group P3̅m1) in which hexagonal nets of RE atoms and [M2As2] slabs built up of edge-sharing M-centered tetrahedra are alternately stacked along the c-direction. For compounds with divalent RE components (Eu, Yb), the fully stoichiometric and charge-balanced formula REM2As2 is obtained, with Mn and Zn atoms statistically disordered within the same tetrahedral site. For compounds with trivalent RE components, the RE sites become deficient, and the Mn atoms are segregated from the Zn atoms in separate tetrahedral sites. Within the series RE1-yMnxZn2-xAs2 (Gd-Tm, Lu), the parent CaAl2Si2-type structure is retained, and the Mn atoms are disordered within partially occupied interstitial sites above and below [Zn2-xAs2] slabs. Within the series RE2-yMnxZn4-xAs4 (RE = La-Nd, Sm, Gd), the c-axis becomes doubled as a result of partial ordering of Mn atoms between every other pair of [Zn2-xAs2] slabs. Attempts to synthesize Gd-containing solid solutions with the charge-balanced formula Gd0.67MnxZn2-xAs2 suggested that these phases could be formed with up to 50% Mn substitution. Band structure calculations reveal that a hypothetical superstructure model with the formula La1.33MnZn3As4 would have no gap at the Fermi level and that slightly lowering the electron count alleviates antibonding Mn-As interactions; a spin-polarized calculation predicts nearly ferromagnetic half-metallic behavior. X-ray photoelectron spectroscopy confirms the presence of divalent Mn in these compounds.
    Inorganic Chemistry 07/2014; 53(16). DOI:10.1021/ic501053v · 4.79 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The pnictides EuCd2X2 (X = P, As, Sb) and YbCd2Sb2 were synthesized from the elements or a EuCd2 precursor in tantalum tubes. The samples were characterized by powder X-ray diffraction. The structure of EuCd2As2 was refined on the basis of single-crystal X-ray diffractometer data: CaAl2Si2 type, Pm1, a = 444.99(9), c = 735.0(1) pm, wR2 = 0.0372, 200 F2 values and 10 variables. The two-dimensional [Cd2X2] networks consist of edge-sharing CdX4/4 tetrahedra. The networks are separated and charge-balanced by the europium and ytterbium atoms. Redetermination of the magnetic properties revealed divalent europium and ytterbium. YbCd2Sb2 is diamagnetic. For the europium compounds only one magnetic phase transition is evident, i.e. TC = 11.6 K for EuCd2P2, TN = 9.5 K for EuCd2As2, and TN = 7.4 K for EuCd2Sb2. 151Eu Mössbauer spectra show full magnetic hyperfine field splitting at 4.2 K. A transferred hyperfine field of 7.1 T is evident in the 4.2 K 121Sb spectrum of EuCd2Sb2.
    Zeitschrift für anorganische Chemie 10/2011; 637(12). DOI:10.1002/zaac.201100179 · 1.25 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The novel complex pnictides Ba4Li2Cd3Pn6 (Pn = P, As and Sb) have been synthesized by direct combination of the respective elements at high temperature, and structurally characterized by single-crystal X-ray diffraction. The three isostructural compounds crystallize with their own structure type in the centrosymmetric orthorhombic space group Cmcm (Pearson code oC60). The crystal structure is based on one-dimensional infinite chains of supertetrahedral clusters, [Cd4Pn10], running parallel the a-axis. These chains are connected through Pn2-type dumbbells. Tight-binding electronic structure calculations show that the electronic stability of these compounds requires strong covalent Pn–Pn and Cd–Pn bonds. The interactions within the polyanionic sub-structure are complimented by weaker Ba–Pn and Li–Pn bonds, which also show a substantial degree of covalency, and the strength of all interactions correlates very well with the corresponding interatomic distances. The precise satisfaction of the valence rules and the Zintl–Klemm concept is not essential though as structural vacancies on Cd and Li sites bring about an interplay between ionicity and covalency among the electronegative components. Electronic structure calculations show that Ba4Li2Cd3P6 is expected to be a semiconductor with a band gap of ca. 0.5 eV, while the gap decreases and vanishes altogether for the As- and Sb-analogs, respectively. Solid solutions between arsenides and antimonides appear possible, which could be an effective way to fine-tune transport properties. Since the latter two compounds can be considered as moderately-to-heavily doped intrinsic semiconductors, these materials might be suitable candidates for thermoelectric applications.
    Berichte der deutschen chemischen Gesellschaft 10/2014; 2014(30). DOI:10.1002/ejic.201402434