Calculated X‐ray Diffraction Data for Diamond Polytypes

Abstract

Calculated X-ray diffraction pattern data for diamond polytypes are presented, which provides the required parameters for the characterization of the proposed diamond polytypes. The literature on diamond polytypes contains some small but significant errors with respect to the details of the crystal structure, including space groups, the atom positions in the unit cell, and the atomic layer stacking. In this paper, the crystal structures of four different hexagonal diamond and two different rhombohedral diamond polytypes are theoretically calculated to provide correct crystallographic information with which the diamond polytypes in a given sample can be characterized. [

Nanocrystalline diamond synthesized from C60

“…Compression of fullerene C 60 under non-hydrostatic pressures to 25-30 GPa at room temperature has resulted in direct transformation to diamond, probably with small crystallite sizes [13,14], but the amount of synthesized material was insufficient for detailed characterisation of the structure or mechanical properties and the reproducibility of such experiments has come under scrutiny [15,16]. Numerous nanocluster-based phases with presumably 3D-polymerized fullerite structures have been synthesized from C 60 and carbon singlewall nanotubes at pressures above 13 GPa and temperatures above 800 K [15][16][17]. These new materials show impressive mechanical properties and some of them appeared to be harder than diamond [15,16].…”

X‐Ray Induced Synthesis of 8H Diamond

“…The unit cell parameters are fully consistent with the electron diffraction data ( Table 2). The calculated density of 3.67 g cm À3 (after the problems in the crystal structure table are resolved, then this density value might need to be recomputed) is similar to but greater than that of both cubic diamond and lonsdaleite (3.52 g cm À3 ), [3,14] which suggests the existence of compressive stress, as discussed below. Both nanosized particles and compressive stress can produce broadening and slight shifts of the X-ray peaks consistent with the slight mismatch of some peaks in the observed and simulated patterns.…”

“…[2] Subsequent chemical vapor deposition (CVD) diamond studies have led to the observation of additional polytypes, including 4H, 6H, 8H, and 15R. [3][4][5][6][7][8][9][10] In these materials, particle size fractions range from 1000 nm down to 10 nm, and the phases are always mixed (e.g., 2H, 6H, 8H, and 3C). Recently, carbon nanotubes have been compressed to over 100 GPa, creating a single hard hexagonal phase dominated by sp 3 -bonding.…”

“…As computed in the local density approximation of density functional theory, the energy differences as a function of volume between the three polymorphs 2H, 8H, and 3C are relatively similar. The volume is in bohr 3 (1 bohr ¼ 0.529177 Å) and the energy in hartrees (1 Ha ¼ 27.2116 eV). The inset shows cross-sections through the valence electron density.…”

Analysis of the Intermediate Layers Generated at the Film-Substrate Interface During the CVD Process of Diamond Synthesis

“…INTRODUCTION The potentially new technological applications expected for diamond deposited on different substrates in the form of extended surfaces, coating and layers, have stimulated an enormous interest in the CVD techniques of diamond synthesis under reduced-P/reduced-T conditions [1,21. The nonequilibrium conditions developed in the course of such kinetically driven processes can yield a variety of solid-state carbon species [3]. It is believed that the nucleation kinetics of specific interface structures generated during the early stages of the synthesis plays a decisive role in phase selection 14-81.…”