Using the Inverse Proximity Effect to Increase the Tc of YBCO

15 August 2025
Superconductors.ORG

        Recently Superconductors.ORG reported a direct link had been found between dielectric constant (relative permittivity K) of lattice substructures and the transition temperature (Tc) of a superconductor. However, reformulation is necessary to employ this mechanism to increase Tc, which is not always possible. Now, it's been found that the inverse proximity effect (IPE) can accomplish the same result in some high temperature superconductors - like YBCO - without reformulation. High permittivity ferroelectrics like lead-zirconate-titanate (PZT) and barium-titanate (BT) have been found to promote the Tc of YBCO by simply being in close contact.

       In the two magnetization plots at page top a 50-50 mix of YBCO powder⁽¹⁾ and either PZT or BT powder⁽²⁾ are shown. Both adjuncts increased the Tc of YBCO by 11-14 degrees⁽³⁾ — without any sintering. And, since industrial grade YBCO is normally fabricated as a thin film, this method may lend itself to epitaxial bonding of a thin film of ferroelectric material to YBCO. Already many manufacturers are using the insipient ferroelectric STO (strontium-titanate) as a growth substrate. Unfortunately, STO only improves the Tc of YBCO by 2 degrees, from 91 to 93 Kelvin.

       Tests also revealed that YBCO formulations that have already been improved by other means, can still benefit from IPE. For example, YBCO-Mg (YBa2Cu2MgO7+) increased its Tc from 100.5K to 105.0K (see below right). And there was no vestige of the original Tc in any of the plots. So the volume fraction is as high as the original formulation.

       With the critical transition temperature of YBCO now approaching that of BSCCO, IPE could be a game-changer for these competing superconductor products. Efforts to improve the Tc of BSCCO by use of IPE failed. So its Tc remains unimproved at 108 Kelvin.

1. A commercial grade YBCO test pellet was obtained from Colorado Superconductor, Fort Collins, CO., and then ground into a fine powder.

2. The PZT powder was PZT-8 (PbZr_0.53Ti_0.47Sr_.08O_3.1). The BT was barium titanate powder (BaTiO₃, 99.9% purity, 325 mesh), obtained from Chemsavers, Bluefield, VA.

3. Testing temperatures were determined using an Omega type "T" thermocouple. The magnetometer employed a Honeywell SS94A1F Hall-effect sensor with a sensitivity of 25 mv/Gauss.

E. Joe Eck
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