Comparing XRDspectra (Figure 1) of the products
synthesized by the C-H method at 120, 160, and 200∘C for
12 h with the JCPDS database (WO3, No. 72-1465) [19], they
corresponded with pure monoclinic crystal system and P21/n space group at the synthesis temperatures of 160 and 200∘C
for 12 h.