A 2 B 2 O 7 -type oxides with low thermal conductivities are potential candidates for next-generation thermal barrier coatings. The formation of high-entropy ceramics is considered as a newly effective way to further lower their thermal conductivities. High-entropy Y 2 (Ti 0.2 Zr 0.2 Hf 0.2 Nb 0.2 Ta 0.2 ) 2 O 7 (5HEO) and Y 2 (Ti 0.25 Zr 0.25 Hf 0.25 Ta 0.25 ) 2 O 7 (4HEO) ceramics were prepared by in situ solid reaction sintering, considering the important roles of B-site cations on thermal conductivities of the A 2 B 2 O 7 -type oxides. Reaction process, phase structures, microstructures, and thermal conductivities of the as-sintered ceramics were investigated. Lattice distortion effects on their thermal conductivities were also discussed by using the proposed criterion based on the supercell volume difference of the individual compounds. Near fully-dense 5HEO and 4HEO ceramics were obtained after being sintered at 1600 • C. The former one had a dual-phase structure containing high-entropy Y 2 (Ti 0.227 Zr 0.227 Hf 0.227 Nb 0.136 Ta 0.182 ) 2 O 7.318 pyrochlore oxide (5HEO-P) and Y(Nb, Ta)O 4 solid solution, while the latter one was a single-phase pyrochlore oxide (4HEO-P) with homogeneous element distribution. The formed 5HEO-P oxide has larger lattice distortion than 4HEO-P oxide due to the larger total amounts of Nb and Ta cations at B sites in the 5HEO-P oxide. It results in lower thermal conductivity of 5HEO ceramics (keeping at 1.8 W⋅m -1 ⋅K -1 ) than those of 4HEO ceramics (ranging from 1.8 to 2.5 W⋅m -1 ⋅K -1 ) at temperatures from 25 • C to 1400 • C. Their glass-like thermal conductivities were determined by the selection of B site cations and high-entropy effects. These results provide some useful information for the material design of novel thermal barrier coating materials.

Neutral open-structured metal phosphites of Al and In are hydrothermally synthesized; they are structural analogues that constructed by HPO3 and MO6 groups with intersecting eight- and 10-ring channels. The two metal sites serve as four- and five-connected centers, respectively, with the rest oxygen atoms belonging to the coordinated water molecules.

Two new open-framework zincophosphites, Zn(H 6 C 4 N 2 S)(HPO 3 ) (TJPU-4) and [C 6 N 2 H 14 ] · [Zn 3 (HPO 3 ) 4 ] (TJPU-5) have been hydrothermally synthesized by using 2-mercapto-1-methylimidazole [MMI] and 1,4-diazabicyclo[2.2.2]octane [DABCO] as templates. TJPU-4 crystallizes in monoclinic space groupP2 1 /c with the cell parameters a ϭ 8.787(4) Å , b ϭ 9.732(4) Å , c ϭ 10.515(4) Å , β ϭ 105.316(6)°, V ϭ 867.3(6) Å 3 . The structure of TJPU-4 is constructed by ZnO 3 S tetrahedron and HPO 3 pseudo-pyramid to generate a layer of 4, 8-network in bc plane. The organic template locates on the both sides of the 8membered rings and bonds to zinc atom through ZnϪS bond. TJPU-5 crystallizes in the triclinic space group P1 with cell param-

Two Neutral Open-Framework Metal Phosphites with Ten-Ring Channels Constructed by Three-, Four-, and Five-Connected Centers. -Two isostructural open-framework phosphites, [M2(H2O)3(HPO3)3]·H2O (M: Al, In) are hydrothermally synthesized from mixtures of Al(NO3)3 or InCl3, H3PO3, cyclohexanebis(methylamine) and H2O (pH 1.5-2, 180°C, autoclave, 6 d) and characterized by powder and single crystal XRD. The compounds crystallize in the monoclinic space group P21 with Z = 2. The structure contains HPO 3 and MO 6 groups with intersecting eight-and 10-ring channels. -(YANG, Y.; ZHAO*, Y.; YU, J.; PANG, N.; SU, H.; PANG, S.; Chem. Lett.