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The thermoelectric performance of EuCd2Sb2 and YbCd2Sb2 was improved by mixed cation occupation. The composition, structure, and thermoelectric properties of YbxEu1-xCd2Sb2 (x=0, 0.5, 0.75, and 1) have been investigated. Polycrystalline samples are prepared by direct reaction of the elements. Thermoelectric properties were investigated after densification of the materials by spark plasma sintering. YbxEu1-xCd2Sb2 crystallizes in the P3m1 space group. The lattice parameters increase with the europium content. These materials show low electrical resistivity, high Seebeck coefficient, and low thermal conductivity together with high carrier concentration and high carrier mobility. ZT values of 0.88 and 0.97 are obtained for Yb0.5Eu0.5Cd2Sb2 and Yb0.75Eu0.25Cd2Sb2 at 650 K, respectively. [ABSTRACT FROM AUTHOR]

Rare earth metal borides have attracted great interest due to their unusual properties, such as superconductivity and f-electron magnetism. A recent discovery attributes the tunability of magnetism in rare earth aluminoborides to the effect of so-called "building defects." In this paper, we report data for the effect of building defects on the thermal conductivities of α-TmAlB4 single crystals. Building defects reduce the thermal conductivity of α-TmAlB4 by ≈30%. At room temperature, the thermal conductivity of AlB2 is nearly a factor of 5 higher than that of α-TmAlB4. AlB2 single crystals are thermally anisotropic with the c-axis thermal conductivity nearly twice the thermal conductivity of the a-b plane. Temperature dependence of the thermal conductivity near and above room temperature reveals that both electrons and phonons contribute substantially to thermal transport in AlB2 with electrons being the dominant heat carriers. [ABSTRACT FROM AUTHOR]

Unexpectedly strong magnetic coupling is observed in boride insulators containing the B12 icosahedra as a structural unit. We have successfully synthesized Dy0.74B22C2N, which takes the RB22C2N-type crystal structure. The Dy phase was previously thought to not be possible to form. Spin glass-like behavior was observed with a broad peak in the zero field cooled (ZFC) magnetic susceptibility at T ∼ 44 K, while a large divergence for ZFC and field cooled (FC) curves is observed. The Curie-Weiss constant is determined to be θ=-43.9 K, and this system is indicated to have the strongest magnetic coupling ever observed for any rare earth boride insulator. Electronic structure and chemical bonding calculations were also made. Conventional mechanisms for f-electron magnetism cannot explain the strong coupling observed, which further indicates that the B12 icosahedra is functioning as a novel mediator of magnetic interaction. [ABSTRACT FROM AUTHOR]

With a counterintuitive approach to crystal growth, single crystals of α-TmAlB4 were successfully grown, which were indicated from transmission electron microscopy (TEM) and x-ray diffraction (XRD) measurements and analysis to be virtually free from the ubiquitous building defects, and their properties investigated. Recent developments in rare earth aluminoboride compounds with two-dimensional boron layers have attracted interest due to the heavy fermion superconductivity in β-YbAlB4, multiple anomalies manifesting below the Néel temperatures in α-TmAlB4 attributed to intrinsic building defects, and field stable state in Tm2AlB6. The physical properties of the obtained α-TmAlB4 crystals show a striking difference from the properties of conventional α-TmAlB4 crystals containing building defects. TN = 6.8 K is revealed to be higher than the 5.8 K formerly thought, and the multiple anomalies below TN are replaced by a sharp λ-like peak in the specific heat C. The large effect of the building defects on the physical properties could be directly confirmed, and strikingly it is shown how the large peak structure in the specific heat of the high quality sample could be destroyed by the presence of a small amount (one or two percent) of building defects. [ABSTRACT FROM AUTHOR]

The thermoelectric performance of EuCd2Sb2 and YbCd2Sb2 was improved by mixed cation occupation. The composition, structure, and thermoelectric properties of YbxEu1-xCd2Sb2 (x=0, 0.5, 0.75, and 1) have been investigated. Polycrystalline samples are prepared by direct reaction of the elements. Thermoelectric properties were investigated after densification of the materials by spark plasma sintering. YbxEu1-xCd2Sb2 crystallizes in the P3m1 space group. The lattice parameters increase with the europium content. These materials show low electrical resistivity, high Seebeck coefficient, and low thermal conductivity together with high carrier concentration and high carrier mobility. ZT values of 0.88 and 0.97 are obtained for Yb0.5Eu0.5Cd2Sb2 and Yb0.75Eu0.25Cd2Sb2 at 650 K, respectively. [ABSTRACT FROM AUTHOR]

The thermoelectric performance of EuCd(2)Sb(2) and YbCd(2)Sb(2) was improved by mixed cation occupation. The composition, structure, and thermoelectric properties of Yb(x)Eu(1-x)Cd(2)Sb(2) (x=0, 0.5, 0.75, and 1) have been investigated. Polycrystalline samples are prepared by direct reaction of the elements. Thermoelectric properties were investigated after densification of the materials by spark plasma sintering. Yb(x)Eu(1-x)Cd(2)Sb(2) crystallizes in the P3m1 space group. The lattice parameters increase with the europium content. These materials show low electrical resistivity, high Seebeck coefficient, and low thermal conductivity together with high carrier concentration and high carrier mobility. ZT values of 0.88 and 0.97 are obtained for Yb(0.5)Eu(0.5)Cd(2)Sb(2) and Yb(0.75)Eu(0.25)Cd(2)Sb(2) at 650 K, respectively.

Polycrystalline EuZn(2)Sb(2) is prepared by direct reaction of the elements. Its composition, structure, magnetism, heat capacity, and thermoelectric properties have been investigated. EuZn(2)Sb(2) crystallizes in p3m space group with a=4.4932(7) A and c=7.6170(10) A. Antiferromagnetic ordering is detected at the Neel temperature of 13.06 K, and the saturation magnetization reaches 6.87mu(B)Eu at 2 K and 7 T. Eu ion has +2 valence. Its Hall effects are characterized by a high positive Hall coefficient of +0.226 cm(3)C, proper carrier concentration of 2.77x10(19)cm(3), and high carrier mobility of 257 cm(2)V s at 300 K. This compound shows high p-type Seebeck coefficient (+122 to +181 muVK), low lattice thermal conductivity (1.60-0.40 Wm K), and high electrical conductivity (1137-524 Scm). The obtained figure of merit and powder factor reach 0.92 and 20.72 muWcm K(2), respectively. The thermoelectric properties of EuZn(2)Sb(2) are encouraging.