Rapid HPHT annealing of synthetic IB-TYPE diamonds

V.N Kazuchits,N.M Kazuchits,M.S Rusetskiy,O.V Korolik,A.V Konovalova,O.V Ignatenko

doi:10.1016/j.carbon.2020.12.002

Abstract

The paper provides the information on the effects of rapid (1 min) high pressure high temperature (RHPHT) annealing of synthetic Ib-type diamond plates at temperatures (1900 °C, 2100 °C, 2300 °C, 2500 °C, 2700 °C) and pressure of 8 GPa. The studies were carried out using the visual analysis, absorption and Raman spectroscopy, photoluminescence and cathodoluminescence. During RHPHT annealing the diamond plates in a high-pressure container were rapidly heated/cooled at a very non-uniform temperature and pressure distribution. All this caused the inhomogeneous plastic deformation of diamond plates. The plastic deformation of diamonds during RHPHT annealing was a powerful “generator” of vacancies. The electron transfer from individual atoms of substituting nitrogen to nitrogen-vacancy centers switched these centers to a negatively charged state. Another accompanying RHPHT annealing process was the diffusion of nitrogen atoms with the formation of it’s simple aggregates – H3 defects (at 2300 °C). At higher RHPHT annealing temperatures more complex aggregates containing three nitrogen atoms – N3 defects — were generated. RHPHT annealing led to the formation of identical nitrogen – vacancy defects, as did quasi stationary HPHT annealing, but the number of these defects was significantly greater after RHPHT annealing.

Highlights

The heat treatment is a common method of controlling diamond properties.Since a diamond at normal pressure is a metastable phase of carbon, it undergoes spontaneous graphitization when heated
Modern advances in diamonds annealing technology without pressure allow it to be carried out at high temperatures when impurity nitrogen atoms become mobile [5,6,7,8,9]
Research methods A 12x magnification optical microscope was used for the visual analysis and photographing of diamond plates

Summary

Introduction

The heat treatment (annealing) is a common method of controlling diamond properties. Since a diamond at normal pressure is a metastable phase of carbon, it undergoes spontaneous graphitization when heated. The low-temperature annealing in which intrinsic interstitials, vacancies, and hydrogen become movable, can be carried out at normal pressure and without graphitization in the nitrogen or inert gas atmosphere. Modern advances in diamonds annealing technology without pressure allow it to be carried out at high temperatures (low pressure high temperature - LPHT annealing) when impurity nitrogen atoms become mobile [5,6,7,8,9]. The graphitization by LPHT annealing in pure hydrogen atmosphere [7, 10] or in vacuum [11] is significantly suppressed. It is impossible to completely get rid of graphitization despite the significant success of LPHT annealing technology

Methods

Results

Conclusion