Giant negative thermal expansion covering room temperature in nanocrystalline GaNxMn3

Abstract

Materials with negative thermal expansion (NTE), which contract upon heating, are of great interest both technically and fundamentally. Here, we report giant NTE covering room temperature in mechanically milled antiperovksite GaN x Mn 3 compounds. The micrograin GaN x Mn 3 exhibits a large volume contraction at the antiferromagnetic (AFM) to paramagnetic (PM) (AFM-PM) transition within a temperature window (ΔT) of only a few kelvins. The grain size reduces to ~ 30 nm after slight milling, while ΔT is broadened to 50K. The corresponding coefficient of linear thermal expansion (α) reaches ~ -70 2 ppm/K, which is almost two times larger than those obtained in chemically doped antiperovskite compounds. Further reducing grain size to ~ 10 nm, ΔT exceeds 100 K and α remains as large as -30 ppm/K (-21 ppm/K) for x = 1.0 (x = 0.9). Excess atomic displacements together with the reduced structural coherence, revealed by high-energy Xray pair distribution functions, are suggested to delay the AFM-PM transition. By controlling the grain size via mechanically alloying or grinding, giant NTE may also be achievable in other materials with large lattice contraction due to electronic or magnetic phase transitions.

Giant negative thermal expansion across the first-order magnetoelastic transition in Hf0.86Ta0.14Fe2

“…In majority of these systems the NTE region is limited by the width of the magnetic transition which is usually narrow in bulk samples. This NTE temperature span can be enhanced by processing the material to broaden the transition, for instance by converting it into nanocrystalline form for applications [23,53,57,58]. The NTE properties can be tailored by the control of the microstructure scale.…”

“…Recently, the utilization of a magnetic transition accompanied by large volume contraction upon heating is deemed as a promising avenue towards discovery of giant NTE. The effectiveness of this approach was recognized widely by the giant NTE observed on the Mn3AN-based antiperovskite manganese nitrides [9,23,24,55,56,58] which use volume change due to the magnetic phase transition, i.e., magnetovolume effects. The giant NTE of the antiperovskite manganese nitrides strongly influenced subsequent research, leading to the discovery of many phase-transition-type NTE compounds such as MnCo0.98Cr0.02Ge [30] and La(Fe,Si,Co)13 [31], which display large magnetovolume effects.…”

Spray‐dry synthesis of β‐Cu1.8Zn0.2V2O7 ceramic fine particles showing giant negative thermal expansion

“…[3][4][5][6][7][8][9] Nevertheless, technical difficulties persist in the fabrication of NTE fine particles. Many reports of earlier studies [10][11][12][13] have described that the NTE function is drastically altered by fine particles: The magnitude of the negative coefficient of thermal expansion is degraded, although the temperature window for NTE is expanded. Regarding manganese nitrides, NTE properties are noticeably affected even at the level of several micrometers.…”

Tunable negative thermal expansion and structural evolution in antiperovskite Mn3Ga1−xGexN (0 ≤ x ≤ 1.0)

“…Among these manganese antiperovskites, Mn 3 GaN shows many interesting properties in materials with single phase, such as NTE, BME, giant barocaloric effect, spin‐glass (SG), piezomagnetic effect, so, we focus our attention on the Mn 3 GaN. However, the NTE operation temperature range of Mn 3 GaN is relative narrow due to a sharp change, it is unsuitable for actual applications.…”