Introducing protons into potassium tantalate niobate single crystals

Potassium tantalate niobate single crystals are capable of capturing protons in their lattice. We examined this capability via analysis of their O-H absorption spectra in the near infrared region. Protons are captured in the crystals together with oxygen in the form of water molecules. Therefore, when we wish to introduce protons into the crystals, they must contain oxygen vacancies of some kind. The vacancy concentrations for as-grown crystals depend on the melt compositions used for growth. The addition of copper and/or lithium to the melt decreases the vacancy concentration. We were able to increase the concentration either by deoxidizing the melt used for crystal growth, or by post-growth heat treatment.