title: Flux versus Hydrothermal Growth: Polymorphism of A2(UO2)Si2O6(A = Rb, Cs).
abstract: Single crystals of two new uranyl silicates were grown from mixed alkali fluoride/alkali chloride fluxes. Polymorphism is observed in Cs2(UO2)Si2O6, where hydrothermal conditions lead to the α polymorph and flux growth favors the β polymorph. Rb2(UO2)Si2O6crystallizes in a monoclinic distortion of the α-Cs2(UO2)Si2O6structure type with space group I2/a and lattice parameters a = 14.9932(5) Å, b = 14.8032(5) Å, c = 16.2377(9) Å, and β = 90.7220(10)°. β-Cs2(UO2)Si2O6constitutes a new polymorph of Cs2(UO2)Si2O6and crystallizes in the monoclinic space group C2 with lattice parameters a = 12.136(2) Å, b = 10.0426(17) Å, c = 7.7896(13) Å, and β = 95.849(4)°. The two structures are compared, the driving force behind the observed polymorphism is discussed, and the luminescence properties are reported for each compound.
authors.affiliation: Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States.
authors.forename: Gregory
authors.identifier: http://orcid.org/0000-0001-9674-9224
authors.initials: G
authors.lastname: Morrison
authors.affiliation: Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States.
authors.forename: Mark D
authors.initials: MD
authors.lastname: Smith
authors.affiliation: Department of Chemistry and Biochemistry, University of South Carolina , Columbia, South Carolina 29208, United States.
authors.forename: Hans-Conrad
authors.identifier: http://orcid.org/0000-0001-7351-9098
authors.initials: HC
authors.lastname: Zur Loye