TY - JOUR

T1 - A closer look into close packing

T2 - pentacoordinated silicon in a high-pressure polymorph of danburite

AU - Pakhomova, Anna

AU - Bykova, Elena

AU - Bykov, Maxim

AU - Glazyrin, Konstantin

AU - Gasharova, Biliana

AU - Liermann, Hanns-Peter

AU - Mezouar, Mohamed

AU - Gorelova, Liudmila

AU - Krivovichev, Sergey

AU - Dubrovinsky, Leonid

PY - 2017/9

Y1 - 2017/9

N2 - Due to their high technological and geological relevance, silicates are one of the most studied classes of inorganic compounds. Under ambient conditions, the silicon in silicates is almost exclusively coordinated by four oxygen atoms, while high-pressure treatment normally results in an increase in the coordination from four-to sixfold. Reported here is a high-pressure single-crystal X-ray diffraction study of danburite, CaB2Si2O8, the first compound showing a step-wise transition of Si coordination from tetrahedral to octahedral through a trigonal bipyramid. Along the compression, the Si2O7 groups of danburite first transform into chains of vertice-sharing SiO5 trigonal bipyramids (danburite-II) and later into chains of edge-sharing SiO6 octahedra (danburite-III). It is suggested that the unusual formation of an SiO5 configuration is a consequence of filling up the pentacoordinated voids in the distorted hexagonal close packing of danburite-II.

AB - Due to their high technological and geological relevance, silicates are one of the most studied classes of inorganic compounds. Under ambient conditions, the silicon in silicates is almost exclusively coordinated by four oxygen atoms, while high-pressure treatment normally results in an increase in the coordination from four-to sixfold. Reported here is a high-pressure single-crystal X-ray diffraction study of danburite, CaB2Si2O8, the first compound showing a step-wise transition of Si coordination from tetrahedral to octahedral through a trigonal bipyramid. Along the compression, the Si2O7 groups of danburite first transform into chains of vertice-sharing SiO5 trigonal bipyramids (danburite-II) and later into chains of edge-sharing SiO6 octahedra (danburite-III). It is suggested that the unusual formation of an SiO5 configuration is a consequence of filling up the pentacoordinated voids in the distorted hexagonal close packing of danburite-II.

KW - phase transitions

KW - polymorphism

KW - five-coordinate silicon

KW - danburite

KW - silicates

KW - STRUCTURAL-CHARACTERIZATION

KW - CALCIUM SILICATE

KW - REEDMERGNERITE

KW - TRANSFORMATION

KW - 6-COORDINATE

KW - COMPLEXES

KW - CRYSTALS

U2 - 10.1107/S2052252517010612

DO - 10.1107/S2052252517010612

M3 - статья

VL - 4

SP - 671

EP - 677

JO - IUCrJ

JF - IUCrJ

SN - 2052-2525

ER -