Theoretical study of hydration in Y2Mo3O12: Effects on structure and negative thermal expansion

Abstract

We report ab-initio calculations of water absorption in Y2Mo3O12. The absorption geometry of H2O in Y2Mo3O12 and the binding property between H2O and Y2Mo3O12 have been first identified. Our calculated results show that water is chemisorbed in Y2Mo3O12 with O of the water binding to the Y3+ cation, which is further strengthened by hydrogen bonding between each of the hydrogen atoms of H2O and the bridge O in Y2Mo3O12, shared by polyhedrons YO6 and MoO4. The absorption of water leads to a reduced angle of Y-O-Mo and shortened Y-Mo distance, and consequently volume contraction of the material, almost linearly with the increasing number of water molecules per unit cell, up to eight in total. In addition, our phonon calculation show that the transverse vibration of Y-O-Mo is restricted due to water absorption, which in turn hinders the NTE, as it is mainly originated from this vibrational mode. Our results clarify further the fundamental mechanisms of the large volume shrinkage and the lost NTE of the framework oxide due to water absorption.

Red phosphor based on Eu3+-doped Y2(MoO4)3 incorporated with Au NPs synthesized via Pechini's method

“…Marinkovic et al showed that the water molecules occupy microchannels with diameter around 5 Å along c-crystallographic directions in Y 2 (MoO 4 ) 3 structure, leading to a negative thermal expansion in Y 2 (MoO 4 ) 3 [38]. Furthermore, M. Wu et al showed that the water absorption reduces the Y-Mo bond distance, shortening the Y-O-Mo bond angle and consequently reducing the solid volume [41].…”

In situ investigation of the surface morphology evolution of the bulk ceramic Y2Mo3O12 during crystal water release

“…The HRTEM image and the diffraction fringes reflect the real status of the hydrated Y 2 Mo 3 O 12 Á3H 2 O because the crystal waters are not physically adsorbed but are chemically bonded. 22,24 The regular lattice diffraction fringes indicate no lattice distortion in the sample, i.e. fully hydrated Y 2 Mo 3 O 12 Á3H 2 O still presents a periodic structure but the space group is different from the unhydrated Y 2 Mo 3 O 12 reported by Lind et al 20,23 It can be inferred that fully hydrated Y 2 Mo 3 O 12 Á3H 2 O with the space group Pba2 is the most energetically favorable form, and that lattice distortion will occur during the release of crystal water and it will eventually become unhydrated Y 2 Mo 3 O 12 with the space group Pbcn.…”

Structures and Photophysical Characterization of the Samarium-doped Y2Mo3O12 Ceramics

“…Molybdates with a general formula A 2 Mo 3 O 12 family, where A is a trivalent cation, are known to be hosts for transition metal ions and lanthanide ions [1][2][3]. Recently, these materials have attracted lots of attention because of negative thermal expansion (NTE), characterized by chemical exibility and a phase transition, from monoclinic to orthorhombic, depending on the A 3+ cation size [4][5][6][7][8].…”

“…Recently, these materials have attracted lots of attention because of negative thermal expansion (NTE), characterized by chemical exibility and a phase transition, from monoclinic to orthorhombic, depending on the A 3+ cation size [4][5][6][7][8]. These NTE materials are microporous and interstitial cation-free frameworks consisting of vertex-linked AO 6 octahedra and MO 4 tetrahedra, where each AO 6 octahedron joins MO 4 tetrahedra sharing oxygen of their corners [1,9].…”

“…However, NTE materials have not been applied widely because of several disadvantages: hygroscopicity, high phase transition temperature, and metastable structure [11,12]. These hygroscopicity and high phase transition temperature in A 2 Mo 3 O 12 family have been studied widely and achieved progresses in practical applications [13][14][15]: the reduction of hygroscopicity in A 2 Mo 2 O 12 theoretically and experimentally [1,10,11]. Among these molybdates, Y 2 Mo 3 O 12 represents larger NTE because yttrium (Y) has larger ionic radius compared with other trivalent transition metals [9].…”