The high temperature p-type thermoelectric material Yb(14)MnSb(11) has been of increasing research interest since its high temperature thermoelectric properties were first measured in 2006. Subsequent substitutions of Zn, Al, and La into the structure have shown that this material can be further optimized by altering the carrier concentration or by reduction of spin-disorder scattering. Here the properties of the Yb(14-x)Ca(x)MnSb(11) solid solution series where isovalent Ca(2+) is substituted for Yb(2+) will be presented. Crystals of the Yb(14-x)Ca(x)MnSb(11) solid solution series were made by Sn-flux (x = 2, 4, 6, 8) with the following ratio of elements: (14-x)Yb: xCa: 6 Mn: 11Sb: 86Sn, and their structures determined by single crystal X-ray diffraction. The density of the material significantly decreases by over 2 g/cm(3) as more Ca is added (from x = 1 to 8), because of the lighter mass of Ca. The resulting lower density is beneficial from a device manufacturing perspective where there is often a trade-off with the specific power per kilogram. The compounds crystallize in the Ca(14)AlSb(11) structure type. The Ca substitution contributes to systematic lengthening the Mn-Sb bond while shortening the Sb-Sb bond in the 3 atom linear unit with increasing amounts of Ca. Temperature dependent thermoelectric properties, Seebeck, electrical resistivity, and thermal conductivity were measured from room temperature to 1273 K. Substitution of Yb with Ca improves the Seebeck coefficient while decreasing the thermal conductivity, along with decreasing the carrier concentration in this p-type material resulting in an enhanced thermoelectric figure of merit, zT, compared to Yb(14)MnSb(11).

Table of contents: 1. Full details on Rietveld refinements of Yb 14 MnSb 11 , 90-900K 2. Debye-fits of Uiso(T) for Yb 14 MnSb 11 . 3. Various bond distances in Yb 14 MnSb 11 4. PXRD data of Yb 14 MnSb 11 at 400K, 550K and 700K 5. Atomic Hirshfeld surfaces of Yb 14 MnSb 11 6. Comparison of high and low temperature AHS

Single-crystalline samples of a new Zintl compound, Eu(3)Ga(2)P(4), have been synthesized by a Ga-flux method. Eu(3)Ga(2)P(4) is found to crystallize in a monoclinic unit cell, space group C2/c, isostructural to Ca(3)Al(2)As(4). The structure is composed of a pair of edge-shared GaP(4) tetrahedra, which link by corner-sharing to form Ga(2)P(4) two-dimensional layers, separated by Eu(2+) ions. Magnetic susceptibility showed a Curie-Weiss behavior with an effective magnetic moment consistent with the value for Eu(2+) magnetic ions. Below 15 K, ferromagnetic ordering was observed and the saturation magnetic moment was 6.6 μ(B). Electrical resistivity measurements on a single crystal showed semiconducting behavior. Resistivity in the temperature range between 280 and 300 K was fit by an activation model with an energy gap of 0.552(2) eV. The temperature dependence of the resistivity is better described by the variable-range-hopping model for a three-dimensional conductivity, suggesting that Eu-P bonds are involved in the conductivity. A large magnetoresistance, up to -30%, is observed with a magnetic field H = 2 T at T = 100 K, suggesting strong coupling of carriers with the Eu(2+) magnetic moment.

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High resolution single crystal synchrotron X-ray diffraction data measured at 15(2) K were used to solve the structure of the complex intermetallic Zintl phase, Yb(11)AlSb(9) (space group Iba2), made up of Yb cations and polyanions along with isolated Sb anions. The 15(2) K cell parameters are a = 11.7383(4) Å, b = 12.3600(4) Å, c = 16.6796(6) Å. The temperature dependence of the structure was investigated through high resolution synchrotron powder X-ray diffraction (PXRD) data measured from 90 K to 1000 K. Rietveld refinements of the crystal structure revealed near linear thermal expansion of Yb(11)AlSb(9) with expansion coefficients of 1.49(2) × 10(-5) K(-1), 1.71(3) × 10(-5) K(-1), 1.13(1) × 10(-5) K(-1) for a, b and c, respectively. The chemical bonding in Yb(11)AlSb(9) was analyzed using atomic Hirshfeld surfaces, and the analysis supports the presence of the structural elements of Yb cations, [AlSb(4)](9-) tetrahedra, [Sb(2)](4-) dimers and isolated Sb(3-) anions. However, indications of interatomic interactions between the Zintl anions and the Yb cations were also observed.

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Crystals of Yb14‐xCaxMnSb11 (x = 2, 4, 6, 8) solid solutions are prepared by reaction of the elements in a Sn flux (excess Mn, alumina crucible sealed in a quartz tube, 1000 °C).