nanopowders were found to be hexagonal unit cell and matched well with JCPDS

Card No. 09-432 for hydroxyapatite. The mean crystallite size, crystallinity, and

lattice parameters of all as-synthesized nanopowders calculated from XRD diffrac-

tion peaks are given in Table 23.4. The changes in lattice parameters “a” and “c” of

as-synthesized ionic substituted HA nanopowders showed the effect of ionic substi-

tution in HA. Broader diffraction peaks of as-synthesized HA nanopowder indicated

its amorphous nature. Its lattice parameters, i.e., “a” ¼ 9.411 Å and “c” ¼ 6.878 Å,

matched well with hydroxyapatite. Both ZnHA and MgHA nanopowders showed a

decrease in crystallite size. However, ZnHA nanopowder showed an increase in

lattice parameters and MgHA nanopowder showed decrease in lattice parameters as

compared to HA. The changes in lattice parameters with zinc substitution suggested

possible Zn substitution at Ca sites in the apatite lattice. In MgHA nanopowder, a

decrease in the value of lattice parameters was due to smaller ionic radii of Mg

(0.66 Å) with respect to Ca (0.99 Å). EuHA nanopowder showed a decreased value

of lattice parameter “a” and an increased value of lattice parameter “c” as compared

to HA.

The XRD pattern of fluorine-substituted HA nanopowder was compared with

JCPDS Card No. 15-0876 of fluorapatite. The XRD spectra of FHA nanopowder

exhibited an identical behavior as HA.

FHA showed stronger XRD intensities and broader peaks than HA which

indicated its lower crystallinity. The two peaks (211) and (112) combined because

of fluorination. SiHA nanopowder showed increased crystallinity and decreased

lattice parameters of HA on silicon substitution. KSiHA nanopowder showed

“a”-axis contraction as compared to SiHA. But minor expansion of the c-axis was

observed for KSiHA with respect to SiHA. The contraction in the a-axis was due to

the substitution of silicon ion. Although the ionic radius of potassium ion (1.33 Å) is

greater than the ionic radius of calcium ion, the further decrease in lattice parameter

“a” of KSiHA nanopowder was due to the substitution of a bivalent cation (Ca²⁺) by

a monovalent cation (K⁺), resulting in the decrease of channel diameter of “a”

parameter (Kannan et al. 2007). Substitution of Zn and F in HA lattice showed

increased crystallite size and lattice parameters. In MgSrHA nanopowder, XRD

peaks shifted towards lower angle as compared to MgHA. The co-substitution of

magnesium and strontium (MgSrHA) in HA showed lower crystallinity and

increased lattice parameters. Multi-substituted MgSrFHA nanopowder showed vari-

ation in crystallite size and lattice parameters. MgSrFHA showed higher crystallite

size than SrFHA nanopowder. Lattice parameter ‘a’ was smaller whereas lattice

parameter ‘c’ was higher in MgSrFHA than SrFHA.

On heat treatment of as-synthesized nanopowders, change in mean crystallite

size, crystallinity, lattice parameters, and phase transformations were observed

(Fig. 23.5). The change in their respective values is summarized in Table 23.5.

Crystallite size and crystallinity of nanopowders increased with an increase in heat

treatment temperature. At higher heat treatment temperatures, the increase in crys-

tallite size is due to the coalescence of small grains through grain boundary diffusion

(Choodamani et al. 2014). The increase in crystallinity after heat treatment indicates

23

Unleashing Potential of Bone Mimicking Nanodimensional Hydroxyapatites and. . .

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