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Ionic Conductivity In A Thermochromic Solid

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Presentation on theme: "Ionic Conductivity In A Thermochromic Solid"— Presentation transcript:

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-Dependant
h 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

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