Martensitic transformation in V_3Si single crystal: ^51V NMR evidence for coexistence of cubic and tetragonal phases

TL;DR

This study uses ^51V NMR on a high-quality V_3Si single crystal to reveal that the Martensitic transformation involves a microscopic coexistence of cubic and tetragonal phases over a temperature range, with no pre-transformed phase at superconducting transition.

Contribution

It provides direct NMR evidence of phase coexistence during Martensitic transformation in V_3Si, highlighting the transformation's gradual nature and domain formation.

Findings

Martensitic transformation is not abrupt but involves phase coexistence.

No pre-transformed phase exists at the superconducting transition temperature.

Transformation involves domain formation with lengthening perpendicular to the growth axis.

Abstract

The Martensitic transformation (MT) in A15 binary-alloy superconductor V_3Si, though studied extensively, has not yet been conclusively linked with a transition to superconductivity. Previous NMR studies have mainly been on powder samples and with little emphasis on temperature dependence during the transformation. Here we study a high-quality single crystal, where quadrupolar splitting of NMR spectra for ^51V allowed us to distinguish between spectra from transverse chains of V as a function of temperature. Our data revealed that (1) the MT is not abrupt, but rather there is a microscopic coexistence of pre-transformed cubic phase and transformed tetragonal phase over a few K below and above Tm, while (2) no pre-transformed phase can be found at Tc, and (3) the Martensitic lengthening of one axis occurs predominantly in a plane perpendicular to the crystal growth axis, as twinned domains.