To figure out the role of pH in HA synthesis, we
produced HA nanofibers under different initial pH val-
ues. Fig. 3 shows XRD patterns of two samples synthe-
sized at pH = 4 and 9, respectively, which are consistent
with the standard database (1997, JCPDS 73-1731).
Interestingly, with the increase in initial pH value, dif-
fraction peak of (210) crystal plane was enhanced nota-
bly, suggesting that crystal epitaxy changed. The orien-
tation index (p) of HA crystal could be calculated from
the formulae: R = I(210) / I(211) and p = R/R0, where I is the