ARTICLE pubs.acs.org/crystal
Diamond Growth from a PhosphorusCarbon System at High Pressure High Temperature Conditions Yuri N. Palyanov,*,†,‡ Igor N. Kupriyanov,† Alexander G. Sokol,† Alexander F. Khokhryakov,†,‡ and Yuri M. Borzdov† †
Sobolev Institute of Geology and Mineralogy, Siberian Branch of Russian Academy of Sciences, Koptyug ave 3, Novosibirsk, 630090, Russia ‡ Novosibirsk State University, Novosibirsk, 630090, Russia ABSTRACT: Diamond crystallization in phosphoruscarbon systems was studied at high pressures and high temperatures of 6.3 and 7.5 GPa and 14001850 C. To allow for the crystallization kinetics, the run times were set as long as 4060 h. As a result, the range of the pressuretemperature (PT) conditions of diamond nucleation and growth on seeds was considerably extended and the fields of diamond spontaneous nucleation, diamond growth on seeds, and formation of metastable graphite were determined. It is experimentally established that the main parameters governing diamond crystallization processes are pressure, temperature, and run duration. The occurrence of Ca, Mg-phosphate, insoluble to phosphorus melt, is found to affect significantly the growth and morphology of diamond. The phosphate melt adsorbs selectively on the tetrahexahedral {310} faces giving rise to peculiar Æ321æ growth steps. Crystallized diamonds were characterized by Fourier transform infrared (FTIR) absorption and Raman spectroscopy. It is found that with decreasing growth temperature both the strength of continuous absorption in the IR spectra and the width and asymmetry of the diamond Raman line significantly increases. The observed asymmetry of the diamond Raman line is suggested to be due to the Fano-type interference.
’ INTRODUCTION Considerable interest in diamond as a promising material for high-technology applications stems from its exceptional physical and chemical properties. Most of the physical properties of diamond are significantly influenced or completely determined by impurities incorporated in the diamond lattice. It is well-known that boron acts in diamond as a shallow acceptor and produces p-type conductivity. Doping diamond with boron is nowadays a well-developed route to produce p-type semiconducting diamond by both high pressure high temperature (HPHT) and chemical vapor deposition (CVD) growth methods.1 Among doping elements, capable of creating shallow donor states in diamond and producing n-type conductivity, of particular importance is phosphorus. Diamonds doped with phosphorus and exhibiting n-type semiconductor properties have been successfully produced by CVD methods.2,3 At HPHT conditions, the synthesis of P-doped diamonds was realized only from carbon solution in phosphorus melt.4 Phosphorus belongs to the class of elemental nonmetallic solventcatalysts for diamond synthesis. It was experimentally shown that besides the phosphoruscarbon system there are other solvents from this class promising for HPHT diamond synthesis, which include sulfurcarbon,57 seleniumcarbon, and telluriumcarbon8 systems. The original studies on diamond crystallization from various nonmetallic solvents have demonstrated the necessity of extremely high PT parameters (7.58 GPa and about 2000 C) to provide r 2011 American Chemical Society
conversion of graphite to diamond.9 However, subsequent studies showed that PT parameters of diamond synthesis in nonmetallic systems could be significantly decreased.10 It was shown experimentally that these systems are characterized by an induction period preceding nucleation and growth of diamond, and the duration of this induction period increases significantly with decreasing pressure and temperature and can be as high as several tens of hours.11 Experimental studies on diamond crystallization in the phosphorus melt at HPHT conditions and data on characterization of HPHT phosphorus-doped diamonds are quite limited, but have already demonstrated unique features of diamond growth, specific morphology, and properties of crystallized diamonds.4,1215 Taking into account that the significant effect of kinetics on diamond crystallization processes has been experimentally demonstrated for various nonmetallic solvents, in the present work we studied diamond crystallization in the PC systems in experiments with a duration of several tens of hours over a wide range of temperatures from 1400 to 1850 C at pressures of 6.3 and 7.5 GPa.
’ EXPERIMENTAL SECTION Experiments on diamond crystallization in the phosphoruscarbon system were performed using a pressless high-pressure apparatus of the Received: March 21, 2011 Revised: April 21, 2011 Published: April 25, 2011 2599
dx.doi.org/10.1021/cg2003468 | Cryst. Growth Des. 2011, 11, 2599–2605
Crystal Growth & Design
ARTICLE
Table 1. Experimental Resultsa
a
diamond growth
diamond
R, % Gr f Dm
diamond
metastable
on seeds
nucleation
transformation
morphology
graphite
40
þ
þ
100
{111}
40
þ
þ
100
{111}
1700
16
*
þ
40
{111}
7.5
1700
40
þ
þ
100
{111}
P-1235
7.5
1650
23.5
þ
þ
80
{111}
P-1238
7.5
1600
40
þ
þ
80
{111}
P-1239 P-1240
7.5 7.5
1550 1500
40 40
þ þ
þ þ
30 ∼1
{111} {111}
þ
P-1305
7.5
1450
60
þ
þ
