Crystallization of HPHT diamond crystals in a floatage system under the influence of nitrogen and hydrogen simultaneously

Abstract

Employing floatage as a driving force for diamond growth, the crystallization of diamond crystals in a Fe–Cr–C system co-doped with nitrogen and hydrogen elements is established at a static pressure of ~6.5 GPa and a temperature range of 1335–1485 °C. Under the influence of nitrogen and hydrogen incorporated into the diamond structure simultaneously, a rich morphological diversity of diamond specimens is produced, such as hexagonal slice-shape, trapezoidal slice-shape, strip shape and triangular slice-shape crystals. Observation of the infrared spectra of the as-grown crystals indicates that a dramatic enhancement in the simultaneous incorporation of hydrogen and nitrogen atoms into the diamond structures is present in the strip-shape specimens, confirmed by the fact that relatively high absorption coefficients of the peaks at 1130 cm⁻¹, and 1344 cm⁻¹ are accompanied with high absorption coefficients of the bands at 2850 cm⁻¹ and 2920 cm⁻¹. Hydrogen-related absorption in the three-phonon region further indicates that hydrogen atoms exist in the diamond structures as sp³ bonded –CH₂– and –CH₃ group forms. At atmospheric pressure, these hydrogen-containing structures are rather stable and can sustain high temperatures of up to 1800 °C. Nitrogen donors are universally observed as an isolated substitutional form in the crystals, while minor paired-form nitrogen atoms are readily formed in the strip shape crystals or other crystals crystallized at higher temperature.