Negative Thermal Expansion Near the Precipice of Structural Stability in Open Perovskites

Abstract

Negative thermal expansion (NTE) describes the anomalous propensity of materials to shrink when heated. Since its discovery, the NTE effect has been found in a wide variety of materials with an array of magnetic, electronic and structural properties. In some cases, the NTE originates from phase competition arising from the electronic or magnetic degrees of freedom but we here focus on a particular class of NTE which originates from intrinsic dynamical origins related to the lattice degrees of freedom, a property we term structural negative thermal expansion (SNTE). Here we review some select cases of NTE which strictly arise from anharmonic phonon dynamics, with a focus on open perovskite lattices. We find that NTE is often present close in proximity to competing structural phases, with structural phase transition lines terminating near T=0 K yielding the most prominent displays of the SNTE effect. We further provide a theoretical model to make precise the proposed relationship among the signature behavior of SNTE, the proximity of these systems to structural quantum phase transitions and the effects of phase fluctuations near these unique regions of the structural phase diagram. The effects of compositional disorder on NTE and structural phase stability in perovskites are discussed.

On the question of dynamic domains and critical scattering in cubic methylammonium lead triiodide

“…This implies a first-order because the renormalized frequency decreases towards ω 2 0 = 0 for a second-order tran-sition, as seen in SrTiO 3 . [37,38] In fact, as shown in Fig. S12, the lattice parameter exhibits a discontinuous jump at T C , thus confirming the first-order character of the cubic-tetragonal transition in d 6 -MAPI.…”

Auxetic Behavior and Other Negative Thermomechanical Properties from Rotating Rigid Units

“…[134] Apart from the relative simple yet highly elegant explanation of NTE through the RUM approach, what is remarkable is the large variety of NTE materials that can be represented by this model, as detailed in various reviews on the topic. [51,88,90,130] In a parallel development, the 1990s also saw the first reports where a negative Poisson's ratio started to be attributed to rotating rigid units. In fact, Yeganeh-Haeri et al's [126] work on negative Poisson's ratio in α-cristobailite speaks of "rotations of SiO 4 tetrahedra as the structure is compressed," and the work by Keskar and Chelikowsky [128] states that it is possible to "demonstrate that the rigidity of the SiO 4 tetrahedral units is intimately related to the occurrence of negative Poisson ratios in crystalline forms of silica."…”

“…This system, from a geometric perspective, has strong similarities with the auxetic “rotating triangles.” [ 134 ] Apart from the relative simple yet highly elegant explanation of NTE through the RUM approach, what is remarkable is the large variety of NTE materials that can be represented by this model, as detailed in various reviews on the topic. [ 51,88,90,130 ]…”

“…Such “negative” systems, defined in Figure , which have been at the core of what we now call “mechanical metamaterials” and “architected materials,” expand laterally (get fatter) when uniaxially stretched (negative Poisson's ratio, or auxetic [ 1 ] ) rather than shrinking, [ 1–41 ] expand rather than contract in at least one direction when subjected to a compressive hydrostatic pressure (negative linear compressibility), [ 12,42–50 ] or shrink rather than expand when heated (negative thermal expansion). [ 12,51–99 ] Apart from being fascinating from an academic perspective, these anomalous “negative” materials are known to be useful in various practical applications. For example, auxetics (see various recent reviews and monographs [ 100–111 ] ) are potentially superior to conventional materials in applications as diverse as sports, [ 112,113 ] textiles, [ 26 ] filtration, [ …”

Negative and Near-Zero Thermal Expansion in A2M3O12 and Related Ceramic Families: A Review

“…The ability of thermomiotic materials to counteract PTE is also affected by the fact that vibrational NTE is related to proximity to dynamic instability, and therefore pressure-induced phase transitions are common (Occhialini et al, 2018). These phase transitions can cause significant reductions in volume and the magnitude of the CTE, and therefore, in combination with the pressure-induced softening described above, present a significant challenge to the use of materials which exhibit vibrational NTE in composites (Holzer and Dunand, 1999;Zhou et al, 2017), especially those using stiff PTE components.…”