CRYSTALLOGRAPHIC DATA OF A NEW PHASE OF DICALCIUM SILICATE

Unit-cell parameters and the space group of a new phase of dicalcium s ilicate (Ca2SiO4) were determined by using powder X-ray diffractometry and selected-area electron diffraction techniques. This phase could b e synthesized via the dissociation of hydrothermally synthesized alpha -Ca-2(SiO4H)OH at temperatures of similar to 500 degrees-920 degrees C , Crystallographic data for the sample synthesized at 600 degrees C we re as follows: Ca2SiO4, monoclinic; P2(1)/c space group; lattice param eters of a = 0.82147(9) nm, b = 0.9808(1) mm, c = 0.9741(1) nm, and be ta = 94.642(7)degrees; cell volume (V) of 0.7857(1) nm(3); Z = 8 (wher e Z is the number of chemical formula units in a unit cell); and a den sity of 2.91 g/cm(3). The crystallographic data for samples synthesize d at 800 degrees C had slightly different unit-cell parameters of a = 0.82124(6) nm, b = 0.97348(7) nm, c = 0.97935(7) nm, beta = 94.831(5)d egrees, and V = 0.7849(1) nm(3). Structural relationships of the new p hase with the other dicalcium silicates are discussed.