caa a22 4500 378881817 CHVBK 20180305123433.0 cr unu---uuuuu 161128e20030601xx s 000 0 eng 10.1524/zkri.218.6.421.20727 doi (NATIONALLICENCE)gruyter-10.1524/zkri.218.6.421.20727 Room- and high-temperature single crystal diffraction studies on γ-Na2Si2O5: an interrupted framework with exclusively Q3-units [Elektronische Daten] [V. Kahlenberg, S. Rakić, C. Weidenthaler] Single crystals of γ-Na2Si2O5 have been obtained from the crystallization of a stoichiometric glass at 520 °C. The monoclinic crystals belong to space group C2/c (a = 33.326(2) Å, b = 14.1457(7) Å, c = 26.206(2) Å, β = 108.60(2)°, V = 11709.0(1.5) Å3, Z = 96, Dcalc = 2.48 g cm-3). The diffraction pattern showed the typical features of a superstructure. The structure was solved by direct methods including the pseudo-translational effects as a prior information for the normalization process and subsequently refined to a residual of R1 = 0.058. The compound can be classified as an interrupted tetrahedral framework with exclusively Q3-units. Basic building units are spiral achter single chains running parallel [010]. Every four of these chains are linked via common corners, surrounding a central tunnel where the sodium atoms are located for charge compensation. The framework density has a value of 16.4 T-atoms/1000 Å3. At 563°C the monoclinic phase undergoes a structural phase transition into a tetragonal high temperature modification (space group I41/a, a = 11.869(2) Å, c = 7.176(2) Å, V = 1011.0(6) Å3, Z = 4). The transition is induced by cooperative rotations of the tetrahedra and involves a bisection of the translation period along the spiral chains. The symmetries of both modifications are in a close relationship: the space group of the RT-phase is a subgroup of index 24 of the space group of the HT-phase. Focussing on the connectivity of the tetrahedra the two phases are identical and can be characterized as defect—cristobalites where 20 of the tetrahedra have been removed. Topologically they can be described as three dimensional 3-connected nets of a type which has been already observed in the intermetallic compounds LiGe and LiSi, as well as in the mineral grumantite. © 2003 Oldenbourg Wissenschaftsverlag GmbH Crystallography nationallicence Inorganic chemistry nationallicence Organic chemistry nationallicence Kahlenberg V. aut Rakić S. aut Weidenthaler C. aut Zeitschrift für Kristallographie - Crystalline Materials De Gruyter Oldenbourg 218/6(2003-06-01), 421-431 2194-4946 218:6<421 2003 218 zkri https://doi.org/10.1524/zkri.218.6.421.20727 text/html Onlinezugriff via DOI 1 research article jats NATIONALLICENCE 856 40 https://doi.org/10.1524/zkri.218.6.421.20727 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Kahlenberg V. aut NATIONALLICENCE 700 1- Rakić S. aut NATIONALLICENCE 700 1- Weidenthaler C. aut NATIONALLICENCE 773 0- Zeitschrift für Kristallographie - Crystalline Materials De Gruyter Oldenbourg 218/6(2003-06-01), 421-431 2194-4946 218:6<421 2003 218 zkri CC0 http://creativecommons.org/publicdomain/zero/1.0 nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-gruyter