1. Ionic Conductivity In A Thermochromic Solid
Objectives:
--to synthesize the ionic conductor Cu2HgI4
--to observe thermochromism and ionic conductivity in
different phases of a non-molecular inorganic solid

2. Close-Packed Ions

3. Sites (Voids,Vacancies, Holes) in Close-Packed Structures

5. Face-Centered Cubic Unit Cell
--smallest repeating volume element
--one ion on every face of the cube

6. ZnS Cu2HgI4 Voids and conduction
Disordered high-T (right) and ordered low-T (left) unit cell of Cu2HgI4. In the disordered phase, there are on average two Cu+ ions and one Hg2+ ion for every four Iˉ anions. However, the positions of these cations are not fixed – in any given unit cell, it is expected that these three cations will occupy a random subset of the four potential tetrahedral Cu/Hg sites.
Cu2HgI4
Single (left) and doubled (right) unit cell of ZnS (zinc blende structure)
Voids and conduction

7. Ionic Conduction Two cations of the same size, different charge:
which held less tightly by lattice?
Smaller charge
Two cations of same charge, different sizes:
- which moves more easily through lattice?
Smaller size

8. Resistance: Dimension-Dependanth w l
Experimental Apparatus: cylinder of Cu2HgI4

9. Resistivity R = Resistance (experimentally determined), units = 
 = Dimensionless Resistivity (calculate)
units = W cm
measure length in cm of sample
calculate cross-sectional area of sample
Area of a circle = r2 where r = radius of *sample*

10. Conductivity  = Conductivity (calculate)
units = S cm-1
Siemens = 1/W
--Show that ionic conductivity varies for same compound in
different phase
--Determine how changing phase changes conductivity

11. Experimental --Hg Compounds Safety: Gloves at all times
Do not create or breathe dust
*Keep benches, balances, clean*! Clean up spills
at once.
Dispose of gloves in solid waste container.

12. Summary --Synthesis of an infinite, non-molecular solid in two
different phases
--Differences in physical properties with phase change:
1) color
2) ionic conductance