Tengå Andreas, Lidin Sven, Belieres Jean-Philippe, Newman N, Wu Yang, Häussermann Ulrich
Inorganic Chemistry, Stockholm University, SE-10691 Stockholm, Sweden.
J Am Chem Soc. 2008 Nov 19;130(46):15564-72. doi: 10.1021/ja805454p.
The metastable binary intermetallic compound Cd4Sb3 was obtained as polycrystalline ingot by quenching stoichiometric Cd-Sb melts and as mm-sized crystals by employing Bi or Sn fluxes. The compound crystallizes in the monoclinic space group Pn with a = 11.4975(5) A, b = 26.126(1) A, c = 26.122(1) A, beta = 100.77(1) degrees, and V = 7708.2(5) A(3). The actual formula unit of Cd4Sb3 is Cd13Sb10 and the unit cell contains 156 Cd and 120 Sb atoms (Z = 12). Cd4Sb3 displays a reversible order-disorder transition at 373 K and decomposes exothermically into a mixture of elemental Cd and CdSb at around 520 K. Disordered beta-Cd4Sb3 is rhombohedral (space group R3c, a approximately = 13.04 A, c approximately = 13.03 A) with a framework isostructural to beta-Zn4Sb3. The structure of monoclinic alpha-Cd4Sb3 bears resemblance to the low-temperature modifications of Zn4Sb3, alpha- and alpha'-Zn4Sb3, in that randomly distributed vacancies and interstitial atoms of the high-temperature modification aggregate and order into distinct arrays. However, the nature of aggregation and distribution of aggregates is different in the two systems. Cd4Sb3 displays the properties of a narrow gap semiconductor. Between 10 and 350 K the resistivity of melt-quenched samples first increases with increasing temperature until a maximum value at 250 K and then decreases again. The resistivity maximum is accompanied with a discontinuity in the thermopower, which is positive and increasing from 10 to 350 K. The room temperature values of the resistivity and thermopower are about 25 mohms cm and 160 microV/K, respectively. Flux synthesized samples show altered properties due to the incorporation of small amounts of Bi or Sn (less than 1 at. %). Thermopower and resistivity appear drastically increased for Sn doped samples. Characteristic for Cd4Sb3 samples is their low thermal conductivity, which drops below 1 W/mK above 130 K and attains values around 0.75 W/mK at room temperature, which is comparable to vitreous materials.
通过对化学计量比的Cd-Sb熔体进行淬火，获得了亚稳二元金属间化合物Cd4Sb3的多晶锭，并通过使用Bi或Sn助熔剂获得了毫米尺寸的晶体。该化合物结晶于单斜空间群Pn中，a = 11.4975(5) Å，b = 26.126(1) Å，c = 26.122(1) Å，β = 100.77(1)°，V = 7708.2(5) ų。Cd4Sb3的实际化学式单元为Cd13Sb10，晶胞包含156个Cd原子和120个Sb原子（Z = 12）。Cd4Sb3在373 K时表现出可逆的有序-无序转变，并在约520 K时放热分解为元素Cd和CdSb的混合物。无序的β-Cd4Sb3为菱面体（空间群R3c，a约 = 13.04 Å，c约 = 13.03 Å），其骨架与β-Zn4Sb3同构。单斜α-Cd4Sb3的结构与Zn4Sb3的低温变体α-和α'-Zn4Sb3相似，即高温变体中随机分布的空位和间隙原子聚集并有序排列成不同的阵列。然而，两种体系中聚集和聚集体分布的性质不同。Cd4Sb3表现出窄带隙半导体的性质。在10至350 K之间，熔体淬火样品的电阻率首先随温度升高而增加，直到在250 K时达到最大值，然后再次下降。电阻率最大值伴随着热功率的不连续，热功率为正且从10到350 K增加。电阻率和热功率的室温值分别约为25 mΩ·cm和160 μV/K。助熔剂合成的样品由于掺入少量的Bi或Sn（小于1 at.%）而表现出改变的性质。对于Sn掺杂的样品，热功率和电阻率显著增加。Cd4Sb3样品的特征是其低热导率，在130 K以上降至1 W/(m·K)以下，在室温下达到约0.75 W/(m·K)的值，这与玻璃材料相当。
