Presentation on theme: "Ionic Conductivity In A Thermochromic Solid Objectives: --to synthesize the ionic conductor Cu 2 HgI 4 --to observe thermochromism and ionic conductivity."— Presentation transcript:
Ionic Conductivity In A Thermochromic Solid Objectives: --to synthesize the ionic conductor Cu 2 HgI 4 --to observe thermochromism and ionic conductivity in different phases of a non-molecular inorganic solid
Sites (Voids,Vacancies, Holes) in Close-Packed Structures
Face-Centered Cubic Unit Cell --smallest repeating volume element --one ion on every face of the cube
ZnS Single (left) and doubled (right) unit cell of ZnS (zinc blende structure) Disordered high-T (right) and ordered low-T (left) unit cell of Cu 2 HgI 4. In the disordered phase, there are on average two Cu + ions and one Hg 2+ 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. Cu 2 HgI 4 Voids and conduction
Ionic Conduction Two cations of the same size, different charge: – which held less tightly by lattice? Smaller charge Smaller size Two cations of same charge, different sizes: - which moves more easily through lattice?
Resistance: Dimension- Dependant l w h Experimental Apparatus: cylinder of Cu 2 HgI 4
Resistivity = Dimensionless Resistivity (calculate) R = Resistance (experimentally determined), units = units = cm 1)measure length in cm of sample 2)calculate cross-sectional area of sample Area of a circle = r 2 where r = radius of *sample*
Conductivity = Conductivity (calculate) units = S cm -1 Siemens = 1/ --Show that ionic conductivity varies for same compound in different phase --Determine how changing phase changes conductivity
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.
Summary --Synthesis of an infinite, non-molecular solid in two different phases --Differences in physical properties with phase change: 1) color 2) ionic conductance