The Premartensitic Transitions of Titanium Nickel: Observation of a Charge Density Wave in a Binary Alloy

The appearance of a charge-density wave (CDW) and associated phase transitions has been identified in TiNi(Fe), a binary alloy. Bulk thermal and transport measurements have revealed that the "pre-martensitic instability" is composed of two distinct phase transitions. In TiNi(3.2% Fe), these occur at 232 K and 224 K. The Fe impurities are added to produce a large temperature separation between these transitions and the martensitic transformation. Elastic neutron diffraction and x-ray diffraction measurements have shown that the 232 K transition is associated with the appearance of incommensurate 1/3(1-d)(110) and 1/3(102d)(111) superlattices with d(DBLTURN).005 at the onset. The displacements of the 1/3(110) and 1/3(111) superlattices are transversely and longitudinally polarized, respectively. This transition is second order and is associated with a discontinuous change in the slope of the magnetic susceptibility. At 224 K, the lattice undergoes a sudden rhombohedral distortion which makes the lattice and superstructure commensurate. This transition is coincident with the prominent specific heat and resistivity anomalies. On further cooling, the rhombohedral distortion increases, but the superlattice remains commensurate. The total distortion is small; at 200 K, alpha is 89.5 degrees. The crystal domains in the rhombohedral phase according to a random choice of the dilated body diagonal.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2015

Author dc:creator

• Meichle, Michael Eric

• Physics, Condensed Matter

Language dc:language

eng

Identifier

(UMI)AAI8127643

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/77208