Anomalous Thermal Expansion in Superconducting Mg1− x Al x B2 System

Abstract

The thermal lattice expansion in the superconducting Mg 1-x Al x B 2 system (x=0, 0.13 and 0.59) has been measured using high-resolution X-ray powder diffraction. An unusual large negative

Direct observation of charge re-distribution in a MgB2 superconductor

“…A crossover can be observed at T NTE ∼50 K, where the positive thermal expansion (PTE) changes to NTE, whereas it remains approximately constant below 40 K. The anisotropic NTE effects are observed in the region of 40 to 50 K. The solid lines depict the NTE coefficients of α a = 3.477 × 10 −5 K −1 and α c =2.397×10 −5 K −1 , respectively. The fitting results exhibit changes in the basal plane of NTE to be about 1.45 times larger than the c-axis, confirming the unexpectedly large and anisotropic NTE behavior in MgB 2 [16][17][18]. A change in thermal expansion at T C is expected from the Ehrenfest relation for a second-order phase transition.…”

Peierls-type structural phase transition in the low-dimensional superconductor Sc3CoC4

“…Up to now, a wide and diverse field of compounds is known, where small structural changes occur that are either in a competition with the onset of superconductivity, leave it unaffected or even lead to its stabilization [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. These structural changes can be subtle and solely indicated by an anomaly in the thermal expansion directly above the T c as exemplified by the broadly known MgB 2 [27][28][29]. But they may also break the rotational and/or translational symmetry of the crystal structure as demonstrated by the trigonal-to-triclinic phase transitions in the Chevrel phases [8-10, 26, 30-32] or the tetragonal-to-orthorhombic phase transitions in the iron-based superconductors [12][13][14][15][16]33].…”