Abstract
Six potassium rare-earth molybdates KRE(MoO4)2 (RE = Tb, Dy, Ho, Er, Yb, and Lu) were synthesized by flux-assisted growth in K2Mo3O10. The crystal structures were determined using single-crystal X-ray diffraction data. The synthesized molybdates crystallize with the ortho-rhom-bic Pbcn space group (No. 60). Trendlines for unit-cell parameters were calculated using data from the current study. The unit-cell parameters a and c increase linearly whereas b decreases with larger RE cations, based on crystal radii. The unit-cell volumes increase linearly and the densities decrease linearly with larger RE cations. The average distances between the RE cations and the nearest O atoms increase with larger cations whereas the average distances of Mo-O and K-O do not show specific trends.
Highlights
MoO3, and K2SO4 at 1000C for 24 h. They reported that crystals containing RE = Tb ! Lu crystallized in the Pbcn space group whereas RE = La and Pr crystallized in the I41/a space group and others were not defined (Wanklyn & Wondre, 1978)
The title KRE(MoO4)2 compounds crystallized in the orthorhombic Pbcn space group and have alternating layers of [RE(MoO4)2]À and K+ ions (Fig. 1a)
The structural parameters in these previous studies are from powder samples whereas the data in this study are from single-crystal studies
Summary
Rare-earth (RE) molybdates have been studied extensively because of their luminescent, magnetoelectric, and ferroelectric properties (Borchardt & Bierstedt, 1967; Axe et al, 1971; Pratap et al, 1987; Ponomarev et al, 1994; Shi et al, 1996; Kut’ko, 2005; Wang et al, 2007; Ponomarev & Zhukov, 2012). The RE molybdates of ARE(MoO4) (A = Li, Na, K, Rb, Cs, Ag) generally crystallize with the tetragonal I41/a space group with the scheelite (CaWO4) structure or the orthorhombic Pbcn space group (Wanklyn & Wondre, 1978; Hanuza & Fomitsev, 1980; Leask et al, 1981; Hanuza et al, 1994; Stedman et al, 1994; Shi et al, 1996; Voron’ko et al, 2004; Kut’ko, 2005; Wang et al, 2007; Mat’aset al., 2010; Poperezhai et al, 2017). The unit-cell parameters of a and c increase while those of b decrease linearly with increasing size of the RE cations (Fig. 2). These trends are shown clearly, there are large deviations from the trendlines for some molybdates including. The unit-cell volumes increase linearly whereas the densities of the phases decrease linearly as the radius of the RE cations increases (Fig. 2)
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