Structural and electrical properties of infinite-layer CaCuO₂ under high pressure

Abstract

The structural and electrical properties of infinite-layer CaCuO 2 (IL CaCuO 2 ) under high pressure at room temperature were studied using a diamond anvil cell by in situ high pressure energy-dispersive X-ray diffraction with synchrotron radiation and by simultaneous resistance and electrical capacitance measurements. The results indicate that the primary crystal structure of IL CaCuO 2 is stable under pressure up to 30 GPa with an anisotropic compressibility. The equation of state of IL CaCuO 2 was obtained from the V/V 0 KP relationship based on the Birch-Murnaghan equation, which gives rise to a bulk modulus B 0 Z96 GPa in the low pressure range below 6 GPa, and B 0 Z186 GPa at pressures from 6 to 30 GPa for IL CaCuO 2 . The resistance and capacitance measurements of IL CaCuO 2 up to 20 GPa revealed several unusual changes. There is an abrupt resistance drop in the pressure range of 3-6 GPa followed by an abnormal hump occurring around 12 GPa with increasing pressure. Corresponding changes were also observed in the dependence of capacitance on pressure. The former drop is attributed to an isostructural phase transition as observed in the synchrotron radiation experiments. The latter is considered to be related to an electronic structure transition resulting from the anisotropic compression of the IL CaCuO 2 unit cell under high pressure. q

Geometric effects in the infinite-layer nickelates

“…The calculated value is 150 GPa, which is similar to that measured in CaCuO 2 and other cuprates (see, e.g., Ref. [39]). Thus, from the lattice parameters obtained for YNiO 2 , the La → Y substitution in these infinite-layer nickelates can be seen as equivalent to a chemical pressure of ∼19 GPa.…”

Possible very high transition temperatures in the infinite-layer ACuO$ _{2} $ cuprate superconductor for A={Mg, Ca, Sr, Ba}: A DFT study

“…The c/a ratio scales with unit-cell volume as c/a ≈ αV + const. with α = 0.0044 Å−3 , which is similar to what is found experimentally 56 . We do not observe any buckling of the CuO 2 layers, as expected on symmetry grounds.…”

“…As expected, these materials become more compressible as the ion-size increases. By comparison Qin et al 56 experimentally determine the bulk moduli of CaCuO 2 to be 96 GPa for P < 6 GPa and 186 GPa for P > 6 GPa, where P denotes (external) pressure. (For comparison with other cuprates, B 0 = 123 GPa for YBa 2 Cu 3 O 7 and 78 GPa for YBa 2 Cu 3 O 6 .…”

“…For example, CaCuO 2 with a unit-cell volume of V = 45.6 Å3 corresponds to an external pressure of P = 9.6 GPa when using the experimental bulk modulus of 186 GPa (Ref. 56) and has the ratio c/a = 0.813. This simulated external pressure has a similar effect on the c/a ratio as that of internal pressure.…”

Growth and interfacial properties of epitaxial CaCuO2 thin films

“…29 However, Ohnishi and co-workers have published that atomically flat substrates with A-site layer termination can be obtained by a thermodynamic equilibrium process of (110)-or (001)-oriented NdGaO 3 (NGO) substrates in air. 30 Despite the very good lattice matching to NGO, i.e., the pseudocubic lattice parameter of NGO amounts to a % 3.86 Å and for CCO a ¼ 3.855 Å , 31 high-quality pseudomorphic growth of CCO on top of NGO is difficult. 15,24,32,33 Possibly, the reduced interfacial growth quality may be influenced by a polarisation mismatch at the interface due to different polarities of the layers.…”