The mechanical relaxation study of polycrystalline MgCNi3

TL;DR

This study investigates the mechanical relaxation spectra of MgCNi3, revealing internal friction peaks linked to carbon atom dynamics, with differences between superconducting and non-superconducting samples, and suggests atomic jumping as a key mechanism.

Contribution

It provides new insights into the atomic relaxation processes in MgCNi3, especially relating to carbon atom behavior and its relation to superconductivity.

Findings

Internal friction peaks at 300 K and 125 K in superconducting MgCNi3

Peak P2 shifts with frequency, indicating thermally activated process

Carbon atom jumping among off-center positions explains P2 behavior

Abstract

The mechanical relaxation spectra of a superconducting and a non-superconducting MgCNi3 samples were measured from liquid nitrogen temperature to room temperature at frequency of kilohertz. There are two internal friction peaks (at 300 K labeled as P1 and 125 K as P2) for the superconducting sample. For the non-superconducting one, the position of P1 shifts to 250 K, while P2 is almost completely depressed. It is found that the peak position of P2 shifts towards higher temperature under higher measuring frequency. The calculated activation energy is 0.13eV. We propose an explanation relating P2 to the carbon atom jumping among the off-center positions. And further we expect that the behaviors of carbon atoms maybe correspond to the normal state crossovers around 150 K and 50 K observed by many other experiments.