Ya. Litvin et al., Diamonds of new alkaline carbonate-graphite HP syntheses: SEM morphology, CCL-SEM and CL spectroscopy studies, DIAM RELAT, 8(2-5), 1999, pp. 267-272
Colorless octahedral diamonds up to 150 mu m in size were spontaneously cry
stallized from carbon solutions in alkaline-carbonate melts in the Na2Mg(CO
3)(2)-graphite and NaKMg(CO3)(2)-graphite systems at pressures of 8-10 GPa
and temperatures of 1700-1800 degrees C, Seeded growth of carbonate-carbon
(CC) diamond layers was realized on both octahedral {111} and cubic {100} f
aces of natural and synthetic "metal-carbon" (MC) diamond single crystals 0
.5-0.7 mm in size. Scanning electron microscopy (SEM) morphology studies cl
early demonstrate that a preferable mechanism of diamond growth from alkali
ne CC melts is the deposition of newly formed layers in parallel with octah
edral faces, in much the same way as in the case of natural diamonds. A col
or cathodoluminescence (CL) SEM study shows that the specific feature of th
e CC diamonds is the lack of surface color CL as for natural diamonds of ty
pe II with lower nitrogen concentration. The CL spectra of the CC diamonds
consist of three-band system H3, 575 nm, and a weak blue A-band. The struct
ure of the H3 band closely resembles that of natural diamonds of type IIa.
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