Infrared study of OH− defects in KTiOPO4 crystals

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Abstract
Variations in the concentrations and distributions of the OH−defects present in flux and hydrothermal KTiOPO4 (KTP) crystals, measured by infrared spectroscopy of single crystals, are attributed to differences in the growth environments and other nonhydrogenic defects present in the crystals. The concentrations of OH− have been estimated from the infrared data to be approximately 400 ppma (parts per million atomic) (3.0×1019 cm−3) in the flux crystals, 1100–1500 ppma (0.74–1.1×1020 cm−3) in the high‐temperature hydrothermal and 600 ppma (4.3×1019 cm−3) in the low‐temperature hydrothermal crystals. A 3566 cm−1 peak and a 3575 cm−1 band are observed in all crystals. The integrated intensity of the OH− absorption band at 3566 cm−1 increases at the expense of the 3575 cm−1 band at higher temperatures in the high‐temperature hydrothermal crystals. Several OH− peaks (3490, 3455, 3428, 3420, and 3333 cm−1), which have strongly temperature‐dependent linewidths, are present in the hydrothermally grown KTP crystals. The temperature dependencies of their peak frequencies and widths are consistent with the presence of mobile protons in the lattice. The protons located in the 3490 and 3428 cm−1 sites are believed to contribute to the ionic conductivity of the high‐conductivity high‐temperature hydrothermal crystals.