THE TRICLINIC ROOM-TEMPERATURE MODIFICATION OF K2MGWO2(PO4)(2)

K2MgWO2(PO4)(2) [dipotassium magnesium tungsten dioxide bis(phosphate) ; abbreviated formula KMgWP], a new compound crystal-chemically deriva ble from the well known nonlinear optical crystal KTiOPO4 (KTP), under goes at least five phase transitions between its melting point (T-m si milar or equal to 1068 K) and room temperature. KMgWP's triclinic room -temperature structure (space group P1) can be described as a slightly distorted modification of its tetragonal high-temperature phase (T > 782 K), which is isostructural with K2NiWO2(PO4)(2) (KNiWP, space grou p P4(1,3)2(1)2).