Introduction and properties
PtO2 exists in three crystalline phases, α-PtO2, β-PtO2 and a theoretical phase β’-PtO2. Unlike α-PtO2 and other Group 8 metal dioxides, β-PtO2 has an orthorhombic CaCl2 -structure. β-PtO2 is a black, highly insoluble solid, and it is the most stable out of the PtO2 -variations under standard temperature and pressure. Stability of the peculiar orthorhombic crystal structure of β-PtO2 is due to strong hybridization between 2p-orbital of oxygen and 5d-orbital of platinum. When the densities of states curves are drawn for both β-PtO2 (CaCl2) and β’-PtO2 (rutile), an absence of a peak at the fermi level can be observed for β-PtO2. This results in a pseudo-gap in the fermi level, possibly causing interesting properties. However, there is currently very little experimental data on β-PtO2. Some physical properties of β-PtO2 are listed in table 1.
Table 1. Properties of β-PtO2 
Molecular weight [u]
Bulk modulus [GPa]
Band gap (theoretical) [eV]
β-PtO2 crystallizes in the orthorhombic CaCl2 -structure, which is similar to a tetragonal rutile structure, but with small distortions in the directions of a- and b- axes. The tetragonal rutile structure could in theory be obtained when β-PtO2 is heated over 1240 K, resulting in a variation called β’-PtO2. In β-PtO2, the each Pt atom is coordinated to six O atoms and each O atom to three Pt atoms.  The structural information of β-PtO2 is listed in table 2, and the structure is illustrated in figures 1 and 3. A comparison between orthorombic CaCl2 structure and tetragonal rutile structure is shown in figure 2. The simulated XRD powder pattern is shown in figure 4.
Table 2. Structural information of β-PtO2 
Space group (Space group number)
Unit cell volume [Å3]
Lattice parameters [Å]
a = 4.484
b = 4.536
c = 3.136
α = β = γ = 90°
Figure 1. Structure of β-PtO2, on the left ball-stick model (ionic radii), on the right polyhedral model (atomic radii). Red balls represent oxygen, gray balls represent platinum. (Figure: Sini Suurnäkki)
Figure 2. Comparison between CaCl2- and rutile-structure. (Figure: Sini Suurnäkki)
Figure 3. Structure of β-PtO2 viewed from a-, b-, and c- axes, respectively. Red balls represent oxygen, gray balls represent platinum. (Figure: Sini Suurnäkki)
Figure 4. XRD powder pattern of β-PtO2. (Figure: Sini Suurnäkki)
Single crystals can be obtained via high pressure synthesis. Before inventing high pressure synthesis, the precise crystal structure β-PtO2 was unknown, because it could only be synthesized in powder form. β-PtO2 crystals have been synthesized in a temperature of 1500 °C and pressure of 4 kbar, from Pt – KClO3 -mixtures.
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