Syntheses and Structures of (Ga1-xBx)PO4, with a New Modification of High Cristobalite,and (B1-xZnx)PO4, with Low Cristobalite Type

The transition metal element substitutions of the industrial catalytic material ortho-borophosphate, BPO₄, can lead to either new type of structure for Cr^1] or stabilize low cristobalite structure for Mn, Fe,Co, Ni and Cu^2] Here we report our results on the substitution by main group elements Zn and Ga. The two title compounds were synthesized by high temperature solid state reactions and the structure were refined by powder diffraction methods.The structure parameters:(B_0.25Ga_0.75)PO₄:Tetragonal, P-4, a=4.727(1), c=7.078(1) Å,V=158.17(1) ų, Z=2, R(P)=0.0965, R(I)=0.0426; (B_0.61Zn_0.39)PO₄:Orthorhombic, C222₁ a=7.080(1), b=7.087(1),c=6.990(1) Å, V=350.71(2) ų, Z=4,R(P)=0.0904,R(I)=0.0438. Pure GaPO₄ were found three kinds of structures, low- and high-cristobalite and high -quartz with an observation of an unknown unstable high cristobalite at high temperature^3] The boron substitution of the high-cristobalite GaPO₄ with space group I-A leads to lower symmetry space group(P-4). We assume the low symmetry structure related to the unknown unstable phase. The structures of both compounds are similar to very well known cristobalite (see figure below).