Humidity effect on hydration of CsLiB6O10 nonlinear optical crystal: X-ray diffraction study

•Cesium lithium borate crystals were kept under the relative humidity of 15–77%.•At RH 45% or lower, water molecules are incorporated into CLBO structure.•As a result symmetry reduces from I-42d to I-4 without the loss of crystal quality.

Cesium lithium borate crystals (CLBO) grown from melt were kept under the relative humidity of 15–77%. At RH 45% or lower, water molecules are incorporated into CLBO structure resulting in symmetry reduction from I4¯2d to I4¯ without the loss of crystal quality. At higher humidity, crystal degradation is caused by the presence of liquid water on its surface as a result of capillary condensation.