High-purity La3-xTe4 Material with Superior Thermoelectric Performance Synthesized via Te-vapor Transport and Solid-State Diffusion.

La3-xTe4 is a very promising high-temperature candidate applied in next-generation Radioisotope Thermoelectric Generators (RTGs). Conventional synthesis of such materials is based on the mechanochemical method, which makes the sample difficult to purify due to the high-energy ball milling. In this report, a novel synthetic method is developed, which utilizes Te-vapor transport and solid-phase diffusion to efficiently produce the RE3-xTe4 phases (RE = La, Ce, Pr, Nd). Notably, this method obviates the requirement for high-energy ball-milling instruments, conventionally indispensable in the mechanochemical syntheses. For as-synthesized La2.74Te4 material, a high figure of merit of 1.5 is achieved at 1073 K, owning to the reduced electronic thermal conductivity with metal impurities well eliminated.

7-[(5,5-Dimethyl-2-oxido-1,3,2-dioxaphosphinan-2-yl)-oxy]-4-methyl-2H-chromen-2-one.

The title compound, C(15)H(17)O(6)P, was obtained from a reaction of 4-methyl-7-hy-droxy-coumarin and 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphinane 2-oxide. There are two mol-ecules in the asymmetric unit in which the benzopyran ring system is almost planar [r.m.s. deviation for each molecule = 0.003 Å]. In the crystal, C-H⋯O hydrogen bonds and π-π stacking inter-actions [with centroid-centroid distances of 3.743 (3) and 3.727 (3) Å] link the two mol-ecules. The dioxaphospho-rinane ring adopts a chair conformation in both asymmetric molecules.

(1-Oxo-2,6,7-trioxa-1-phosphabicyclo-[2.2.2]octan-4-yl)methyl 4-methyl-benzene-sulfonate.

In the title compound, C(12)H(15)O(7)PS, the P atom has a distorted tetra-hedral environment. The P-O-C-C torsion angles deviate significantly from zero [average = 12.0 (3)°], indicating that the bicyclic OP(OCH(2))(3)C cage is strained. In the crystal, weak C-H⋯O inter-actions consolidate the packing.

2-Amino-4,6-dimethyl-pyrimidin-1-ium 1-oxo-2,6,7-trioxa-1λ-phosphabicyclo-[2.2.2]octane-4-carboxyl-ate.

In the title compound, C(6)H(10)N(3) (+)·C(5)H(6)O(6)P(-), the cation and anion are linked by pairs of N-H⋯O hydrogen bonds. There are additional inter-molecular N-H⋯N hydrogen bonds, which generate centrosymmetric tetramers of two cations and two anions.

Ethyl 3-[2-(p-tolyl-carbamothio-yl)hydrazinyl-idene]butano-ate.

The title compound, C(14)H(19)N(3)O(2)S, was obtained from a condensation reaction of N-(p-tol-yl)hydrazinecarbothio-amide and ethyl acetoacetate. The mol-ecule assumes an E configuration; the thio-semicarbazide and ester groups are located on the opposite sides of the C=N bond. The almost planar thio-semicarbazide unit (r.m.s. deviation = 0.0130 Å) is tilted at a dihedral angle of 49.54 (12)° with respect to the benzene ring. Inter-molecular N-H⋯N and N-H⋯S hydrogen bonding stabilizes the crystal structure. The eth-oxy group of the ester unit is disordered over two positions, with a site-occupancy ratio of 0.680 (10):0.320 (10).