Stabilization of the monoclinic phase of KH$_2$PO$_4$ under restricted geometry conditions

From the analysis of X-ray diffraction patterns the crystal structure of KH$_2$PO$_4$ embedded from an aqueous solution into the pore space of porous glass with an average pore diameter of 7 $\pm$ 1 nm was determined. It has been established that at room temperature KH$_2$PO$_4$ nanoparticles crystalizes in a monoclinic structure, which is metastable in bulk KH$_2$PO$_4$ under normal conditions. The characteristic size of potassium dihydrogen phosphate nanoparticles was determined to be (27 $\pm$ 3 nm) in the pores of this matrix.