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K 4 CaSi 6 O 15 —Solving a 90‐year‐old riddle
Author(s) -
Liu Hang,
Hildebrandt Elias,
Krammer Hans,
Kahlenberg Volker,
Krüger Hannes,
Schottenberger Herwig
Publication year - 2021
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.17920
Subject(s) - monoclinic crystal system , stoichiometry , crystallography , melting point , chemistry , differential thermal analysis , crystal structure , powder diffraction , phase diagram , phase (matter) , mineralogy , materials science , diffraction , physics , organic chemistry , optics
Polycrystalline K 4 CaSi 6 O 15 was prepared from (a) solid‐state reactions between stoichiometric mixtures of the corresponding oxides/carbonates and (b) combustion solution synthesis using K‐ and Ca‐nitrates, tetraethyl orthosilicate (TEOS), and glycine (fuel component) as starting reagents. The compound was characterized by powder X‐ray diffraction. Differential thermal analysis indicated that K 4 CaSi 6 O 15 melts congruently at about 956°C. On cooling down from the liquid state, a distinct glass‐forming tendency was observed. Single crystals suitable for further structural investigations were obtained from sinter experiments just below the melting point. Basic crystallographic data are as follows: monoclinic symmetry, space group Pc , a = 6.9299(2) Å, b = 27.3496(9) Å, c = 12.2187(4) Å, β = 93.744(3)°, V = 2310.86(13) Å 3 , Z = 3. The crystal structure of K 4 CaSi 6 O 15 belongs to the group of interrupted framework silicates with exclusively Q 3 ‐units. The tetrahedral network is the first inorganic representative of the so‐called eth ‐type. Charge compensation in the structure is achieved by the incorporation of potassium and calcium cations, which are coordinated by five to nine oxygen ligands. Ninety years after its first mention the present contribution proves the existence of K 4 CaSi 6 O 15 as a stable phase in the ternary system K 2 O–CaO–SiO 2 .