Compressibility and thermal expansion of YBa2Cu3Ox

TL;DR

This study measures the compressibility and thermal expansion of YBa2Cu3Ox single crystals, revealing how oxygen ordering and pressure influence their mechanical properties across temperatures.

Contribution

It provides detailed high-resolution measurements of anisotropic compressibility and thermal expansion, highlighting pressure-induced oxygen ordering effects in YBa2Cu3Ox.

Findings

Bulk modulus decreases at 300 K and is enhanced by pressure due to oxygen ordering.

Thermal expansion indicates a glass transition above 225 K linked to oxygen ordering.

Pressure effects on bulk modulus are anomalously high, explained by internal bond differences.

Abstract

The linear compressibilities and the thermal expansion of an untwinned, nearly optimal doped YBa2Cu3O6.94 single crystal were measured along the three crystallographic axes with a high-resolution dilatometer mounted in a high-pressure cell. The measurements were performed in a temperature range from 50 K to 320 K under hydrostatic gas pressure of maximal 0.65 GPa. At a temperature of 300 K the measured bulk modulus is reduced and shows a very strong enhancement under increasing pressure due to pressure-induced oxygen ordering. This ordering process can also be related to a glass transition seen in the thermal expansion above 225 K. At lower temperatures, when oxygen ordering is frozen, the bulk modulus is increased and shows a significantly reduced enhancement under pressure. This pressure dependence, however, is still anomalous high, probably caused by bonds of extremely different compressibilities within the unit cell. The widely spread literature data of the bulk modulus can be explained by this high pressure dependence.