Acoustic Stimulation of the Formation and Growth of Synthetic Diamonds within the Region of Their Thermodynamic Stability

The influence of ultrasonic exposure on the processes of nucleation and growth of synthetic diamond under high-pressure, high-temperature (HPHT) conditions was investigated. It was shown that an acoustic field with frequencies around 100 kHz and amplitudes of about 1.5–2.5 μm leads to a significant reduction in the energy barrier of the graphite–diamond phase transition, acceleration of stable nucleus formation, and improvement in growth kinetics. Experimental data demonstrate an increase in diamond yield, enhanced monocrystallinity, and reduced structural defectiveness under ultrasonic action. Based on the analysis of processes in the solid phase and at the interfacial region, a physico-mathematical model of the acoustically stimulated phase transition was proposed, taking into account the dynamic change of the critical nucleus radius, reduction of the barrier ΔG*, enhanced diffusion, and increased efficiency of crystal doping with impurities. The results confirm the promise of ultrasonic stimulation as a tool for controlled intensification of HPHT diamond synthesis and optimization of the structure of growing crystals.