Chemistry Reference
In-Depth Information
the
walk
. The extended Zintl-Klemm concept (
EZKC
) and the concept that relates
of oxidation-pressure-temperature effects provide a basis for understanding the
observed transitions.
Keywords Alloys
Cation arrays
Extended Zintl-Klemm concept
High pressure
Metals
Oxides
Phase transitions
Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 135
2 From Fluorite to Spinel: The Structures of Na
2
S
and Their Oxides, Na
2
SO
3
and Na
2
SO
4
..............................................137
2.1 The Cation Array of Thenardite (V-Na
2
SO
4
)
and TiSi
2
: The First “Missing Link” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 140
2.2 Two Parallel Transitions: Olivine
!
Thenardite
!
Spinel
and Ni
2
In
!
TiSi
2
!
MgCu
2
..................................................... 141
2.3 A Possible Mechanism for the Ni
2
In
!
TiSi
2
!
MgCu
2
Transitions . . . . . . . . . . . . . 143
2.4 The Opposite Way: From Olivine to Fluorite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 145
3 The Important Information Contained in Na
2
SO
3
: Its Comparison with Na
2
S ..........146
3.1 Na
2
SO
3
and the Ni
2
Al Alloy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
3.2 A Mechanism for the CaF
2
!
Ni
2
Al Transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 150
3.3 Can the Internal Pressure Be Estimated? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 152
3.4 Na
2
SO
2
: A Hypothetical Compound with the Anti-Fluorite Structure? . . . . . . . . . . . . 154
4 The Complete
Journey
from Fluorite to the Laves Phases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154
5 Oxidation, Temperature and Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 156
6 The Third Missing Link: The Fe
2
P Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159
6.1 Description of BaCl
2
and Its Relation to the CoSn-Type Structure . . . . . . . . . . . . . . . . 161
6.2 The BaCl
2
and LaCl
3
Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 162
6.3 The Ba Subarray in Hexagonal BaCl
2
............................................. 164
6.4 BaCl
2
: The Cotunnite-Type Phase and Its Relation to the Fe
2
P-Type Structure . . . 167
6.5 Oxides Derived from the Fe
2
P Structure: LiNaSO
4
and LiCaPO
4
................. 168
7 The High-Temperature Fe
2
P
Wurtzite Transition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 169
8 The Post-Spinel Structures Under Pressure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 170
8.1 The Structure of Ca
2
SnO
4
and Related Compounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
8.2 Extension to Mn
2
GeO
4
: The Olivine-, Spinel- and Sr
2
PbO
4
-Type Structures . . . . . 176
8.3 Ca
2
SnO
4
and the FeB Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179
9 The Structure of Ba
2
SnO
4
...............................................................183
9.1 The Ca
2
SnO
4
- and Ba
2
SnO
4
-Type Structures and the Decomposition Processes . . 185
9.2 The Phases of CaGe, Ca
2
Ge and the CaGeO
3
and Ca
2
GeO
4
Oxides . . . . . . . . . . . . . . 186
10 The Question of the Charge Transfer Between Cations: Arguments Accounting for the
Structures of the Group 14 Elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 188
11 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193
!
Abbreviations
bcc sc
Body-centred cubic, simple cubic
bct
Body-centred tetragonal
CN
Coordination number
ELF
Electron localization function
