Page 52 - Book Hosokawa Nanoparticle Technology Handbook

1.8 CRYSTAL STRUCTURE FUNDAMENTALS
Table 1.8.1
Crystal symmetries and Bravais lattices.

Crystal symmetry Bravais lattices
α,β,γ≠90°
γ
Triclinic
β
α
Primitive Base Centered
α≠90° α≠90°
β,γ=90° β,γ=90°
γ γ
Monoclinic
β β
α
α
Primitive Base Centered Body Centered Face Centered
a ≠ b ≠ c a ≠ b ≠ c a ≠ b ≠ c a ≠ b ≠ c

Orthorhombic
c c c c
a a a a
b b b b
a ≠ c
c
Hexagonal

a
α,β,γ≠90°
γ
Rhombohedral
β a
a α
a
Primitive Body Centered
a ≠ c a ≠ c
Tetragonal
c c

a a
a a
Primitive Body Centered Face Centered
Cubic a
a a
a a a
a a a
There are two controversial theories for the forma- reasons such as particle diameter and atmosphere.
tion of metastable tetragonal zirconia. One theory The latter is explained schematically in Fig. 1.8.1 [6].
claims that a tetragonal phase forms thermodynami- From this figure, it is easily understood that higher
cally [4, 5] and the other insists that it forms potential or symmetric phase preferentially appears
kinetically [6]. In the former theory a tetragonal before the crystallization of the stable phase when
phase is stabilized by the strain energy originated the nanocrystal forms from homogeneous amor-
from impurity incorporation, surface energy of phous state. Considering the crystallization behavior
nanoparticles and constrained force by the matrix. of nanoparticles, first, very tiny instable pre-
And in the latter theory a tetragonal phase forms particles (precursors) gather with each other to form
preferentially from a cubic phase and exists embryo with a critical size to make a nuclei,
metastably at around room temperature by some followed by the stabilization and crystallization.

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