Silver mercury iodide (β, ordered) Ag₂HgI₄

Unit cell

Lattice constants

a = 6.317 Å, b = 6.317 Å, c = 12.633 Å; α = 90°, β = 90°, γ = 90°

Cell volume

504.1 ų

Atoms in the cell

14 (Hg 2, Ag 4, I 8)

Formula units Z

2

Calculated density

4.77 g cm⁻³

Shortest contact

2.774 Å

Coordination

Hg

CN 4 at 2.77 Å (4 I)

Ag

CN 4 at 2.77 Å (4 I)

I

CN 3 at 2.77 Å (1 Hg + 2 Ag)

About the structure

• A zinc-blende-type I⁻ array in which only three-quarters of the tetrahedral cation sites are occupied, ordered between Ag⁺ and Hg²⁺ at room temperature (tetragonal I-4).
• Above ~50 °C the cations disorder over all the sites and Ag⁺ conductivity jumps by a thousand-fold; the colour changes yellow → orange, so it is also a thermochromic pigment.
• Coordinates from the Crystallography Open Database, entry 1509816 (open data); hydrogen and water sites with partial occupancy below 0.5 are left out.

Atom positions (fractional, one cell)

Z, coordination numbers, distances, density and packing on this page are computed from these coordinates.