Another Complex Oxide, AB2O4 Spinel
• Valence Requirement:
A+2B=8
• A+2B=2+2x3, 1+7, or
1+2x3.5?
• Spinel consists of an
CCP array of ions with
cations occupying 1/8
of T-site and ½ of Osites;
Normal Spinel, AB2O4
• Normal Spinel: Divalent A ions occupy T-sites;
trivalent B ions occupy O-sites; general formula is
AtB2oO4c; unit cell (a0=8.0~8.5) contains 32 O= + 8A2+
+16B3+;
• Typical Example for Normal Spine:
• How Mg2+ and Al3+ are located in MgAl2O4 lattice?
• To Determine lattice parameter based on Tetrahedral
and Octahedral Coordination;
• Check RMg+2, RAl+3 (for desired CN) based on
Shannon’s Paper;
• To understand the site compression of spinel lattice；
• To calculate the theoretical density of spinel；
HW for Normal/Inverse Spinel
• For MgAl2O4 (Normal Spinel)
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Check RMg+2, RAl+3 (for desired CN)；
(i) Determine Lattice Parameter based on (T site-O );
(ii) Determine Lattice Parameter based on (O site-O);
(iii) If it is known lattice parameter from MgAl2O4
Crystal is 8.02Å, please discuss (a) the observed
lattice is determine by Al-O or Mg-O coordination; (b)
what site (T or O) is compressed apparently;
• Calculate the theoretical density based on (i) and (ii);
Inverse Spinel, AB2O4
• Normal Spinel: Divalent A ions occupy T-sites;
trivalent B ions occupy O-sites; general formula
is AtB2oO4c; unit cell (a0=8.0~8.5) contains 32 O=
+ 8A2+ +16B3+;
• Inverse Spinel: A2+ ions switch places with ½ of
B3+ ions; general formula is Bt [AB]oO4c;
• Fe3O4 is good example for Inverse Spinel;
• Why Fe3O4 is a good example for inverse spinel?
• Size dependence for Fe2+, Fe3+ under different
coordination；