Synthesis, characterization, and properties of two new phosphate crystals MZnAl(PO4)2 (M = Na, K) with 3D framework tunnel structures

Autor: Hong-Yan Lu, Chang-Yu Meng, Yunjian Wang, Lei Geng, Hao Wang
Rok vydání: 2020
Předmět:
Zdroj: Journal of Alloys and Compounds. 820:153176
ISSN: 0925-8388
DOI: 10.1016/j.jallcom.2019.153176
Popis: Two new phosphate crystals, MZnAl(PO4)2 (M = Na, K), were successfully synthesized by high temperature solid state reaction method. NaZnAl(PO4)2 crystallizes in the triclinic centrosymmetric space group P-1 (No.2) with the unit cell parameters of a = 8.2050(9) A, b = 8.8142(9) A, and c = 9.4997(10) A, and Z = 4. KZnAl(PO4)2 crystallizes in the monoclinic centrosymmetric space group C2/c (No.15) with the unit cell parameters of a = 13.2906(7) A, b = 13.1956(8) A, and c = 8.6660(5) A, and Z = 8. The major structural characteristics of the two crystals are three-dimensional tunnel frameworks formed from ZnO4, AlO4 and PO4 tetrahedrons by sharing the oxygen atoms with the alkali metal atoms distributed in the tunnels. Interestingly, compared with the structures of MZnAl(PO4)2 (M = Na, K), it can be found that the structural symmetries show a gradually rising tendency from Na to K as a result of cation size effect of alkali metals. The results of UV–vis spectrum and IR spectra measurements indicate that NaZnAl(PO4)2 and KZnAl(PO4)2 have wide optical transmission ranges and large band gaps of 3.70 eV and 3.76 eV, respectively. The thermal analyses show that the two compounds have excellent thermal stability. AC complex impedance spectra were measured and fitted by the equivalent circuit, based on which the relatively low activation energies of 0.56 and 0.49 eV for NaZnAl(PO4)2 and KZnAl(PO4)2 were derived respectively, indicating that the tunnel structures can provide the ion channels and may be potentially used for alkali metal batteries and high temperature ionic conductors.
Databáze: OpenAIRE
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