An Investigation of Oxides of Tantalum Produced by Pulsed Laser Ablation and Continuous Wave Laser Heating

Recent progress has seen multiple Ta₂O₅ polymorphs generated by different synthesis techniques. However, discrepancies arise when these polymorphs are produced in widely varying thermodynamic conditions and characterized using different techniques. This work aimed to characterize and compare Ta₂O₅ particles formed at high and low temperatures using nanosecond pulsed laser ablation (PLA) and continuous wave (CW) laser heating of a local area of tantalum in either air or an ¹⁸O₂ atmosphere. Scanning electron microscopy (SEM) and Raman spectroscopy of the micrometer-sized particles generated by PLA were consistent with either a localized amorphous Ta₂O₅ phase or a similar, but not identical, crystalline β-Ta₂O₅ phase. The Raman spectrum of the material formed at the point of CW laser impingement was in good agreement with the previously established ceramic "H-Ta₂O₅" phase. TEM and electron diffraction analysis of these particles indicated the phase structure matched an oxygen-vacated superstructure of monoclinic H-Ta₂O₅. Further from the point of laser impingement, CW heating produced particles with a Raman spectrum that matched β-Ta₂O₅. We confirmed that the high-temperature ceramic phase characterized in previous work by Raman spectroscopy was the same monoclinic phase characterized in different work by TEM and could be produced by direct laser heating of metal in air.