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A rare-earth-containing compound, ytterbium aluminium antimonide, Yb3AlSb3(Ca3AlAs3-type structure), has been successfully synthesized within the Yb–Al–Sb system through flux methods. According to the Zintl formalism, this structure is nominally made up of (Yb2+)3[(Al1−)(1b– Sb2−)2(2b– Sb1−)], where1band2bindicate 1-bonded and 2-bonded, respectively, and Al is treated as part of the covalent anionic network. The crystal structure features infinite corner-sharing AlSb4tetrahedra, [AlSb2Sb2/2]6−, with Yb2+cations residing between the tetrahedra to provide charge balance. Herein, the synthetic conditions, the crystal structure determined from single-crystal X-ray diffraction data, and electronic structure calculations are reported.

Thermoelectric materials can convert heat into electricity. They are used to generate electricity when other power sources are not available or to increase energy efficiency by recycling waste heat. The Yb21Mn4Sb18 phase was previously shown to have good thermoelectric performance due to its large Seebeck coefficient (∼290 μV K−1) and low thermal conductivity (0.4 W m−1 K−1). These characteristics stem respectively from the unique [Mn4Sb10]22− subunit and the large unit cell/site disorder inherent in this phase. The solid solutions, Yb21Mn4−xCdxSb18 (x = 0, 0.5, 1.0, 1.5) and Yb21−yCayMn4Sb18 (y = 3, 6, 9, 10.5) have been prepared, their structures characterized and thermoelectric properties from room temperature to 800 K measured. A detailed look into the structural disorder for the Cd and Ca solid solutions was performed using synchrotron powder X-ray diffraction and pair distribution function methods and shows that these are highly disordered structures. The substitution of Cd gives rise to more metallic behavior whereas Ca substitution results in high resistivity. As both Cd and Ca are isoelectronic substitutions, the changes in properties are attributed to changes in the electronic structure. Both solid solutions show that the thermal conductivities remain extremely low (∼0.4 W m−1 K−1) and that the Seebeck coefficients remain high (>200 μV K−1). The temperature dependence of the carrier mobility with increased Ca substitution, changing from approximately T−1 to T−0.5, suggests that another scattering mechanism is being introduced. As the bonding changes from polar covalent with Yb to ionic for Ca, polar optical phonon scattering becomes the dominant mechanism. Experimental studies of the Cd solid solutions result in a max zT of ∼1 at 800 K and, more importantly for application purposes, a ZTavg ∼ 0.6 from 300 K to 800 K.

Thermoelectric materials are a unique class of compounds that can recycle energy through conversion of heat into electrical energy. A new 21–4–18 Zintl phase has been discovered in the Yb–Mn–Sb sys...

The MnFeSixP1-x phases (x = 0.30, 0.35, 0.40, 0.48, 0.52, 0.54, 0.56) have been synthesized by arc-melting and subsequent high-temperature sintering. For the first time, single crystals of x = 0.30, 0.40 were successfully grown and analyzed by single crystal X-ray diffraction. Variable temperature X-ray diffraction experiments for x = 0.30 were completed and they show structural changes across the phase transition. Magnetization data revealed that the Curie temperatures and thermal hysteresis values can be tuned according to the Si:P ratio.

A rare-earth-containing compound, ytterbium aluminium antimonide, Yb

${\mathrm{Yb}}_{14}\mathrm{Mn}{\mathrm{Sb}}_{11}$ is a magnetic Zintl compound as well as being one of the best high temperature $p$-type thermoelectric materials. According to the Zintl formalism, which defines intermetallic phases where cations and anions are valence satisfied, this structure type is nominally made up of 14 ${\mathrm{Yb}}^{2+}$, 1 ${\mathrm{MnSb}}_{4}^{9\ensuremath{-}}$, 1 ${\mathrm{Sb}}_{3}^{7\ensuremath{-}}$, and 4 ${\mathrm{Sb}}^{3\ensuremath{-}}$ atoms. When Mn is replaced by Mg or Zn, the Zintl defined motifs become 13 ${\mathrm{Yb}}^{2+}$, 1 ${\mathrm{Yb}}^{3+}$, 1 (Mg, Zn)${\mathrm{Sb}}_{4}^{10\ensuremath{-}}$, 1 ${\mathrm{Sb}}_{3}^{7\ensuremath{-}}$, and 4 ${\mathrm{Sb}}^{3\ensuremath{-}}$. The predicted existence of ${\mathrm{Yb}}^{3+}$ based on simple electron counting rules of the Zintl formalism calls the Yb valence of these compounds into question. X-ray absorption near-edge structure, magnetic susceptibility, and specific heat measurements on single crystals of the three analogs show signatures of intermediate valence Yb behavior and in particular, reveal the heavy fermion nature of ${\mathrm{Yb}}_{14}{\mathrm{MgSb}}_{11}$. In these isostructural compounds, Yb can exhibit a variety of electronic configurations from intermediate ($M=\mathrm{Zn}$), mostly 2+ ($M=\mathrm{Mn}$), to 3+ ($M=\mathrm{Mg}$). In all cases, there is a small amount of intermediate valency at the lowest temperatures. The amount of intermediate valency is constant for $M=\mathrm{Mn}$, Mg and temperature dependent for $M=\mathrm{Zn}$. The evolution of the Yb valence correlated to the transport properties of these phases is highlighted. The presence of Yb in this structure type allows for fine tuning of the carrier concentration and thereby the possibility of optimized thermoelectric properties along with unique magnetic phenomena.

The synthesis, and spectroscopic and structural characterization of bridged dicationic derivatives of benzo-2,1,3-selenadiazoles are reported. The chloride salt of [H4C6NSeN–CH2–CH2–NSeNC6H4]2+ crystallizes forming a macrocyclic structure in which two cations are bridged by Se⋯Cl chalcogen bonds (ChBs), with a third chloride at the centre of the macrocycle. The structure of [1,2-(H4C6NSeN)2-C6H10]Cl2 consists of two selenadiazolium cations linked by a chiral cyclohexane and capped by Se⋯Cl ChBs. Tetrafluoroborate salts of a xylene bridge crystallize in two pseudopolymorphs in which the cations form Se⋯F ChBs in an anti- or syn-conformation. The triflate salt of ethylene-bridged cations dimerizes through the formation of the [Se–N]2 supramolecular synthon with Se⋯O ChBs capping the second selenium atom. In contrast, [H4C6NSeN–CH2–CH2–CH2–NSeNC6H4](CF3SO3)2 only forms Se⋯O ChBs.

Zn–Sb compounds (e.g., ZnSb, β-Zn13Sb10) are known to have intriguing thermoelectric properties, but studies of the Zn3Sb2 composition are largely absent. In this work, α-Zn3Sb2 was synthesized and studied via temperature-dependent synchrotron powder diffraction. The α-Zn3Sb2 phase undergoes a phase transformation to the β form at 425 °C, which is stable until melting at 590 °C. Rapid quenching was successful in stabilizing the α phase at room temperature, although all attempts to quench β-Zn3Sb2 were unsuccessful. The structure of α-Zn3Sb2 was solved using single crystal diffraction techniques and verified through Rietveld refinement of the powder data. α-Zn3Sb2 adopts a large hexagonal cell (R 3 space group, a = 15.212(2), c = 74.83(2) A) containing a well-defined framework of isolated Sb3– anions but highly disordered Zn2+ cations. Dense ingots of both the α-Zn3Sb2 and β-Zn13Sb10 phases were formed and used to characterize and compare the low temperature thermoelectric properties. Resistivity and Seeb...

A conventional solid-state approach has been developed for the synthesis of phase-pure magnetocaloric Mn2–xFexSi0.5P0.5 materials (x = 0.6, 0.7, 0.8, 0.9). Annealing at high temperatures followed by dwelling at lower temperatures is essential to obtain pure samples with x = 0.7, 0.8, and 0.9. Structural features of the samples with x = 0.6 and 0.9 were analyzed as a function of temperature via synchrotron powder diffraction. The Curie temperature, temperature hysteresis, and magnetic entropy change were established from the magnetic measurements. According to the diffraction and magnetization data, all samples undergo a first-order magnetostructural transition, but the first-order nature becomes less pronounced for samples that are more Mn rich.

A conventional solid-state approach has been developed for the synthesis of phase-pure magnetocaloric Mn

The Zn9-δSb7 phase has been identified via high-temperature powder diffraction studies. Zn9-δSb7 adopts two modifications: an α form stable between 514 °C and 539 °C and a Zn-poorer β form stable from 539 °C till its melting temperature of 581 °C. The Zn9-δSb7 structure was solved from the powder data using the simulated annealing approach. Both modifications adopt the same hexagonal structure (P6/mmm) but with slightly different lattice parameters. The α-to-β transformation is abrupt and first-order in nature. The Zn atoms occupy the tetrahedral holes created by Sb atoms. The ideal Zn9Sb7 composition can be explained by its tendency to adopt a charge balance configuration. Out of 7 Sb atoms, 3 Sb atoms form dimers (Sb(2-) ions) and 4 Sb atoms are isolated (Sb(3-) ions), which require 9 Zn(2+) cations for charge neutrality.