Distortions of octahedra in rutile-type structures of transition element dioxides

Realization of a reversible switching in TaO2 polymorphs via Peierls distortion for resistance random access memory

“…Here, using tantalum oxide as an example, we make a thorough exploration of the structures of oxide Ta(IV)O 2 . TaO 2 is generally believed to have a rutile (tetragonal) structure (R-TaO 2 ) [11][12][13], which is more stable than another symmetry I4 1 /a [14]. The present evolutionary structure search and ab initio calculations (computational settings can be found in the Method section) revealed a new stable triclinic TaO 2 phase (symmetry group The phase stability of the two TaO 2 polymorphs are studied by the calculated cohesive energy and their phonon dispersions.…”

“…Here, using tantalum oxide as an example, we make a thorough exploration of the structures of oxide Ta(IV)O 2 . TaO 2 is generally believed to have a rutile (tetragonal) structure (R-TaO 2 ) [11][12][13], which is more stable than another symmetry I4 1 /a [14]. The This indicates that the exchange effect of electron interactions is quite different for these two phases with the same composition.…”

Phase transitions in K-doped MoO2

“…In general, tetragonal structures have small distortions which are typically less than 1%, however monoclinic structures have distortions which can reach up to 8% (this is the case for the VO 2 ). 34 The analyses of the Neutron diffraction data for MoO 2 and K 0.05 MoO 2 show clear distortions of the MoO 6 octahedra in both materials. The distortion for pure MoO 2 at 300 K was 2.63% and change to 2.74% at 200 K, after cooling at 2.2 K/min, which represents approximately 3% difference in this temperature range (the value at 300 K is comparable to those reported by Romanov and Skrobot 34 ).…”

“…34 The analyses of the Neutron diffraction data for MoO 2 and K 0.05 MoO 2 show clear distortions of the MoO 6 octahedra in both materials. The distortion for pure MoO 2 at 300 K was 2.63% and change to 2.74% at 200 K, after cooling at 2.2 K/min, which represents approximately 3% difference in this temperature range (the value at 300 K is comparable to those reported by Romanov and Skrobot 34 ). For K 0.05 MoO 2 , S ¼ 2.90% and 2.40% at 300 and 200 K, respectively, which represent near 18% difference in the temperature range where the peaks in the electrical resistivity measurements occur.…”

“…At 306 K, it is Neutron diffraction measurements performed in MoO 2 and K 0.05 MoO 2 below room temperature show no evidence of structural change from the space group P2 1 /c. However, as pointed out by Romanov and Skrobot, 34 one parameter which characterizes transition metal (M) dioxides is the distortion, S, of the MO 6 octahedra. It measures how much the M-O bonds in the octahedra are different from the average bond.…”