Question

(a) The structure of \(\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7}\) can be described as consisting of rock salt and perovskite layers. Describe the origin of this description. (b) Why is the potential replacement of NbTi by high-temperature superconducting components in M RI equipment of commercial interest?

Short answer

(a) It's based on the structure combining rock salt (Y, BaO) and perovskite (CuO) layers. (b) High-temperature superconductors reduce cooling costs, enhancing MRI efficiency commercially.

Step-by-step solution

Understand the Compound

The compound \(\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7}\), also known as Yttrium barium copper oxide (YBCO), is a high-temperature superconductor. It has a complex crystal structure that can be understood in terms of layers, specifically rock salt and perovskite layers. The rock salt layer typically consists of Y(BaO), and the perovskite layer is composed of stacked CuO sheets.

Rock Salt and Perovskite Layers Description

The rock salt layer in \(\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7} \) looks structurally like a combination of layers of yttrium and barium oxide (Y, BaO), resembling the ionic bonding seen in rock salt (NaCl). The perovskite structure is based on the stacked cuprate sheets, which resemble perovskite-type structures seen in compounds like \(\mathrm{CaTiO}_{3} \).The structure is effectively a transition between these two well-known structures, explained as a combination of the ionic bonding typical for rock salt and the edge-sharing CuO octahedral units characteristic of perovskites.

Commercial Interest in High-Temperature Superconductors for MRI

Typical MRI machines use coils made of NbTi, a low-temperature superconductor. Replacing these coils with high-temperature superconductors like \(\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7}\) can eliminate the need for expensive and complex cryogenic systems necessary for NbTi. High-temperature superconductors operate at higher temperatures, potentially reducing operating costs and increasing efficiency, making them commercially attractive.

Key concepts

YBCO (Yttrium Barium Copper Oxide)

Yttrium Barium Copper Oxide, commonly known as YBCO, is an important member of the high-temperature superconductors family. Unlike traditional superconductors, which require extremely cold temperatures to function, YBCO can operate at relatively higher temperatures. This is due to its unique chemical composition and structure.
YBCO has the chemical formula \(\mathrm{YBa}_{2} \mathrm{Cu}_{3} \mathrm{O}_{7}\) and is composed of yttrium, barium, copper, and oxygen. The combination of these elements creates a material that can conduct electricity without resistance when cooled below its critical temperature. In YBCO, this temperature is around 90 K, which is notably higher than many other superconductors.

• Discovered in 1987, YBCO marked a breakthrough, as its high operational temperature meant liquid nitrogen could be used as a coolant, which is cheaper and more practical than the liquid helium required by lower-temperature superconductors.

This high-temperature capability makes YBCO highly significant in scientific and commercial applications, driving interest in the development and research of superconducting technologies.

Crystal Structure Analysis

In the world of crystallography, understanding the crystal structure of a compound like YBCO is crucial. YBCO's crystal structure can be dissected into layers, famously described as rock salt and perovskite layers. This multi-layered nature is what gives YBCO its unique properties as a superconductor.
The rock salt layer mimics the structure of actual rock salt, where yttrium and barium oxide form an ionic bonding environment which is structurally stable. On the other hand, the perovskite layer consists of copper oxide sheets, each sharing edges and forming octahedral shapes, much like the structure seen in perovskite minerals like \(\mathrm{CaTiO}_{3}\).
These layers work together to facilitate the flow of electricity without loss.

• The rock salt layers provide structural stability.
• The perovskite layers are instrumental in the superconducting ability of YBCO, especially due to the interaction of copper and oxygen atoms within these sheets.

This cumulative structural configuration effectively supports superconductivity by enabling critical electron interactions within the layers.

Commercial Applications of Superconductors

One of the most promising areas for the application of superconductors like YBCO is in magnetic resonance imaging (MRI) technology. Typically, MRI machines use superconducting coils made from low-temperature materials like NbTi. However, these require costly cryogenic systems to maintain the low temperatures necessary for superconductivity.
High-temperature superconductors, such as YBCO, can drastically change this landscape.
Replacing NbTi with YBCO could allow MRIs to operate at higher temperatures, possibly utilizing the more accessible and less expensive liquid nitrogen instead of liquid helium. This substitute could reduce operational costs and simplify system maintenance.

• Leveraging high-temperature superconductors in MRI manufacturing can enhance system efficiency due to reduced cooling requirements.
• It can also lead to more compact designs, essential for medical facilities where space is limited.

Besides medical imaging, high-temperature superconductors hold potential in power transmission, magnetic levitation for trains, and other applications where their efficiency and reduced cooling requirements would be beneficial.