TY - JOUR

T1 - The internal structure of hydrothermally grown leucosapphire crystals

AU - Thomas, Victor G.

AU - Daneu, Nina

AU - Mashkovtsev, Rudolf I.

AU - Rečnik, Aleksander

AU - Fursenko, Dmitry A.

N1 - Publisher Copyright: © The Royal Society of Chemistry.

PY - 2019/2/21

Y1 - 2019/2/21

N2 - This study explores the fine structural details of the boundaries between the growth micro-sectors in a leucosapphire (pure corundum, α-Al 2 O 3 ) crystal grown hydrothermally on a nonsingularly oriented (011) seed. Numerous lamellae along the basal planes of corundum formed on the boundaries of the growth micro-sectors; the thickness of the lamellae ranges from 10 to 30 nm with a length of up to 10 μm. They are composed of an aluminum oxyhydroxide phase, best approximated by the boehmite structure compressed along the c axis by 17% of the initial value of parameter c and stretched along the a and b axes by 12 and 6%, respectively, and therefore called boehmite′. Boehmite′ of the lamellae is epitaxially intergrown with the host leucosapphire (0001) C ‖ (020) B′ . In some lamellae, boehmite′ undergoes a subsequent partial or full topotaxial transformation into corundum, in a twinned or identical orientation with respect to the leucosapphire host. The trigger for this retrograde transition is partial dehydration and reduction of local tensions around the lamellae. Comparison of the results with IR spectroscopic data on synthetic leucosapphire and ruby, grown under identical conditions, showed a complete analogy of sets of absorption lines in the stretch-oscillation region of OH groups. This paper analyses the differences in the internal structure of crystals of both varieties of corundum.

AB - This study explores the fine structural details of the boundaries between the growth micro-sectors in a leucosapphire (pure corundum, α-Al 2 O 3 ) crystal grown hydrothermally on a nonsingularly oriented (011) seed. Numerous lamellae along the basal planes of corundum formed on the boundaries of the growth micro-sectors; the thickness of the lamellae ranges from 10 to 30 nm with a length of up to 10 μm. They are composed of an aluminum oxyhydroxide phase, best approximated by the boehmite structure compressed along the c axis by 17% of the initial value of parameter c and stretched along the a and b axes by 12 and 6%, respectively, and therefore called boehmite′. Boehmite′ of the lamellae is epitaxially intergrown with the host leucosapphire (0001) C ‖ (020) B′ . In some lamellae, boehmite′ undergoes a subsequent partial or full topotaxial transformation into corundum, in a twinned or identical orientation with respect to the leucosapphire host. The trigger for this retrograde transition is partial dehydration and reduction of local tensions around the lamellae. Comparison of the results with IR spectroscopic data on synthetic leucosapphire and ruby, grown under identical conditions, showed a complete analogy of sets of absorption lines in the stretch-oscillation region of OH groups. This paper analyses the differences in the internal structure of crystals of both varieties of corundum.

KW - ELECTRON-DENSITY

KW - HYDROGEN

KW - RUBY

KW - MECHANISM

KW - BOEHMITE

KW - RUTILE

UR - http://www.scopus.com/inward/record.url?scp=85061397351&partnerID=8YFLogxK

U2 - 10.1039/c8ce01796d

DO - 10.1039/c8ce01796d

M3 - Article

AN - SCOPUS:85061397351

VL - 21

SP - 1122

EP - 1129

JO - CrystEngComm

JF - CrystEngComm

SN - 1466-8033

IS - 7

ER -