Interaction of crystal water with the building block in Y2Mo3O12 and the effect of Ce3+ doping

Abstract

Ce(3+) ions are introduced into the lattice of Y2Mo3O12 with a sol-gel method with the aim to reduce its hygroscopicity and pursue the interaction of crystal water molecules with the building block. It is found that Ce(3+) ions occupy the positions of Y(3+) in the lattice and have the function of expelling crystal water molecules in the microchannels so that the number of crystal water molecules decreases significantly as the Ce(3+) content increases and a complete depletion of the crystal water is achieved when the content of Ce(3+) is higher than 8 mol%. Based on the binding energy changes of Mo 3d and Y 3d with and without Ce(3+) in the lattice, the configuration of the crystal water in the building block is deduced, namely, a crystal water serves as a spring with its O(2-) pointing to the Y(3+) in an octahedron and with its H(+) approaching the next nearest O(2-) in the Y-O-Mo bridge. With such a configuration, the effects of the crystal water on the thermal expansion properties of Y2Mo3O12 and the like are explained. It is also shown that the number of crystal water molecules per molecular formula can be quantified by the full width at half maximum of the Raman bands or relative intensity with linear relationships, suggesting that Raman spectroscopy can be a potential tool in quantifying crystal water molecules at room temperature in this or related materials.

Substitutions of Zr4+/V5+ for Y3+/Mo6+ in Y2Mo3O12 for Less Hygroscopicity and Low Thermal Expansion Properties

“…Figure 1a shows the relative linear length change curves of Y 2− x Zr x Mo 3− x V x O 12 (0.0 ≤ x ≤ 1.4). For the sample with x = 0.1 in Y 2− x Zr x Mo 3− x V x O 12 , the thermal expansion property was similar to the reported Y 2 Mo 3 O 12 ( x = 0.0) [22,23], indicating that less substitution of Zr/V for Y/Mo in Y 2 Mo 3 O 12 could not change the crystal structure of Y 2 Mo 3 O 12 . However, for x = 0.3, the thermal contraction and thermal expansion corresponding to the release of adsorbed and crystal water before 476 K reduced remarkably, indicating obvious reduction of the hygroscopicity (Figure 1b) [29].…”

“…Figure 2c shows the Raman spectra of Y 2− x Zr x Mo 3− x V x O 12 . For x = 0.1, there were three primary Raman bonds similar to 940, 821, and 334 cm −1 and that of Y 2 Mo 3 O 12 , due to the presence of crystal water [22,23,25]. Additionally, two weak peaks at 258 and 887 cm −1 were also detected, which should have been related to Zr-O or V-O vibrations.…”

“…Figure 2a shows the XRD patterns of Y 2− x Zr x Mo 3− x V x O 12 at RT with x = 0.0, 0.1, 0.3, 0.5, 1.0, 1.3, and 1.4 (for comparison, the XRD patterns of the samples with x = 0.2, 0.4, and 0.7 are also presented in Figure S1). For x = 0.0, there were only four diffraction peaks corresponding to the fully hydrated form of Y 2 Mo 3 O 12 ·3H 2 O [22,23,24,25]. The XRD spectra had minor changes with the increase of Zr 4+ /V 5+ , without diffraction peaks from other materials (such as ZrMo 2 O 8 , YVO 4 , ZrO 2 , and ZrV 2 O 7 ), which agreed with the results of the thermal expansion.…”

“…NTE could only be present after releasing crystal water. The hygroscopicity of Y 2 Mo 3 O 12 could be reduced by using the ion-substitution (Ce 3+ [22], Fe 3+ [23], La 3+ [24], and (LiMg) 3+ [25]) method. Aliovalent substitution of Mo 6+ and W 6+ for V 5+ in ZrV 2 O 7 does not change its structure [26,27].…”

Near-Zero Thermal Expansion and Phase Transitions in HfMg1−xZnxMo3O12

“…Since most materials expand on heating and contract on cooling, materials with opposite property, namely negative thermal expansion (NTE), are particularly desired for tailoring CTEs. The rediscovery of NTE in ZrW 2 O 8 in a wide temperature range (Evans et al, 1996, 1997a) triggered continuous efforts on understanding the NTE phenomenon and searching for more NTE materials (Yang et al, 2007; Chen et al, 2013, 2015; Tallentire et al, 2013; Lama et al, 2014; Liu et al, 2014; Peng et al, 2014; Xiao et al, 2014; Hu et al, 2015). To date, different families of NTE materials based on various mechanisms, such as the phonon effect (Pryde et al, 1996; Wang et al, 2011; Bridges et al, 2014; Cheng et al, 2016a; Ge et al, 2016a), magnetovolume effect (Takenaka and Takagi, 2005; Qu et al, 2012; Yan et al, 2014), spontaneous ferroelectric polarization (Chen et al, 2013; Peng et al, 2016), and charge transfer (Long et al, 2009; Azuma et al, 2011; Yamada et al, 2016) have been reported.…”