Syntheses, characterization, and theoretical calculation of Rb2Mg3(P2O7)2 polymorphs with deep-ultraviolet cutoff edges

• Published in: Science China materials Vol. 63; no. 4; pp. 593 - 601
• Main Authors: Wu, Hongping, Liu, Shiwei, Cheng, Shichao, Yu, Hongwei, Hu, Zhanggui, Wang, Jiyang, Wu, Yicheng
• Format: Journal Article
• Language: English
• Published: Beijing Science China Press 01.04.2020; Springer Nature B.V
• Subjects: Cations; Chemistry and Materials Science; Chemistry/Food Science; Differential scanning calorimetry; Dimers; First principles; Gravimetry; High temperature; Materials Science; Mathematical analysis; Molecular structure; Phase transitions; Second harmonic generation; Tetrahedra; Ultraviolet spectra; X ray powder diffraction; phosphate; deep-ultraviolet transparent window; polymorphs; structure-property relationship
• ISSN: 2095-8226; 2199-4501
• DOI: 10.1007/s40843-019-1221-0

By the combination of the isolated P 2 O 7 dimers and MgO 4 tetrahedra, α- and β-Rb 2 Mg 3 (P 2 O 7 ) 2 polymorphs were synthesized by a high-temperature solution method. α-Rb 2 Mg 3 (P 2 O 7 ) 2 crystallizes in non-centrosymmetric space group P 2 1 2 1 2 1 , while β-Rb 2 Mg 3 (P 2 O 7 ) 2 crystallizes in centrosymmetric P 2 1 / c . Both structures contain a three dimensional [Mg 3 P 4 O 14 ] 2− anionic framework, while Rb + cations are in the space. Structure analyses show that the isolated P 2 O 7 dimers can easily adjust their variable configurations and orientations to fit the different coordination environments of the cations, which is conducive to the formation of polymorphs. The phase transformation process from α- to β-Rb 2 Mg 3 (P 2 O 7 ) 2 was further investigated by powder X-ray diffraction and thermal gravimetric/differential scanning calorimetry measurements. In addition, UV-vis-NIR diffusion spectra indicate both materials have deep-ultraviolet cut-off edges (below 190 nm). α-Rb 2 Mg 3 (P 2 O 7 ) 2 is second-harmonic generation (SHG)-active and the origin of SHG response was investigated by the SHG density calculations. The first-principle calculations were also carried out to illuminate their structure-property relationships.