Critical Role of Nonrigid Unit and Spiral Acoustical Modes in Designing Colossal Negative Thermal Expansion.

Exploring the relationship between thermal expansion and structural complexity is a challenging topic in the study of modern materials where volume stability is required. This work reports a new family of negative thermal expansion (NTE) materials, AM(CN) with A = Li and Na and M = B, Al, Ga, and In. Here, the compounds of LiB(CN) and NaB(CN) were only synthesized; others were purely computationally studied.

Chemical Framework to Design Linear-like Relaxors toward Capacitive Energy Storage.

ABO-type perovskite relaxor ferroelectrics (RFEs) have emerged as the preferred option for dielectric capacitive energy storage. However, the compositional design of RFEs with high energy density and efficiency poses significant challenges owing to the vast compositional space and the absence of general rules. Here, we present an atomic-level chemical framework that captures inherent characteristics in terms of radius and ferroelectric activity of ions.

Giant uniaxial negative thermal expansion in FeZr alloy over a wide temperature range.

Negative thermal expansion (NTE) alloys possess great practical merit as thermal offsets for positive thermal expansion due to its metallic properties. However, achieving a large NTE with a wide temperature range remains a great challenge. Herein, a metallic framework-like material FeZr is found to exhibit a giant uniaxial (1D) NTE with a wide temperature range (93-1078 K, [Formula: see text]).

Control of Thermal Expansion in TaVO by Double Chemical Substitution.

The control of thermal expansion is an important and challenging issue. Focusing attention on the class of AMO negative thermal expansion (NTE) materials, an approach to control their thermal expansion is still missing. In this work, the thermal expansion of TaVO has been controlled from strong negative to zero to positive by double chemical substitution, i.

Insight into the Relationship between Negative Thermal Expansion and Structure Flexibility: The Case of Zn(CN)-Type Compounds.

High structure flexibility can lead to large negative thermal expansion (NTE), but the reason is not clear. In this work, first-principles calculations have been carried out to investigate the relationship between NTE and structure flexibility in Zn(CN)-type compounds. Smaller bulk modulus corresponds to larger compressibility, thus making the crystal structure more flexible and more suitable for NTE.

Understanding Large Negative Thermal Expansion of NdFe(CN) through the Electronic Structure and Lattice Dynamics.

A large negative thermal expansion (NTE) (α = -4.1 × 10 K, 100-525 K) has been discovered in NdFe(CN). Here, the synchrotron X-ray diffraction and lattice dynamics calculations using the density functional theory were conducted to understand the NTE in NdFe(CN).

Understanding Negative Thermal Expansion of ZnGeO through Local Structure and Vibrational Dynamics.

ZnGeO is a multifunctional material whose intrinsic thermal expansion properties below ambient temperature have not been explored until now. Herein, the thermal expansion of ZnGeO is investigated by synchrotron X-ray diffraction, with the finding that ZnGeO exhibits very low negative (α = -2.02 × 10 K, 100-300 K) and positive (α = +2.

Interplay between local structure, vibrational and electronic properties on CuO under pressure.

The electronic and local structural properties of CuO under pressure have been investigated by means of X-ray absorption spectroscopy (XAS) at Cu K edge and ab initio calculations, up to 17 GPa. The crystal structure of CuO consists of Cu motifs within CuO square planar units and two elongated apical Cu-O bonds. The CuO square planar units are stable in the studied pressure range, with Cu-O distances that are approximately constant up to 5 GPa, and then decrease slightly up to 17 GPa.

Effect of HO Molecules on Thermal Expansion of TiCo(CN).

Understanding the role of guest molecules in the lattice void of open-framework structures is vital for tailoring thermal expansion. Here, we take a new negative thermal expansion (NTE) compound, TiCo(CN), as a case study from the local structure perspective to investigate the effect of HO molecules on thermal expansion. The in situ synchrotron X-ray diffraction results showed that the as-prepared TiCo(CN)·2HO has near-zero thermal expansion behavior (100-300 K), while TiCo(CN) without water in the lattice void exhibits a linear NTE (α = -4.

Negative and zero thermal expansion in α-(CuZn)VO solid solutions.

Negative or zero thermal expansion (NTE or ZTE) of materials is intriguing for controllable thermal expansion. We report a series of orthorhombic α-Cu2-xZnxV2O7 (x = 0, 0.1, 0.

Discovering Large Isotropic Negative Thermal Expansion in Framework Compound AgB(CN) via the Concept of Average Atomic Volume.

Exploring isotropic negative thermal expansion (NTE) compounds is interesting, but remains challenging. Here, a new concept of "average atomic volume" is proposed to find new NTE open-framework materials. According to this guidance, two NTE compounds, AgB(CN) and CuB(CN), have been discovered, of which AgB(CN) exhibits a large NTE over a wide temperature range (α = -40 × 10 K, 100-600 K).

Strong Negative Thermal Expansion in a Low-Cost and Facile Oxide of CuPO.

Negative thermal expansion (NTE) behaviors have been observed in various types of compounds. The achievement in the merits of promising low-cost and facile NTE oxides remains challenging. In the present work, a simple and low-cost CuPO has been found to exhibit the strongest NTE among the oxides (α ∼ -27.

Negative thermal expansion in cubic FeFe(CN) Prussian blue analogues.

Negative thermal expansion (NTE) behavior is an interesting physical phenomenon, but the number of NTE materials is limited. In this study, a new NTE compound has been found, FeFe(CN)6 Prussian blue analogue, where the average linear coefficient of thermal expansion (αl) is -4.260 × 10-6 K-1 between 100 and 450 K.

Large Negative Thermal Expansion Induced by Synergistic Effects of Ferroelectrostriction and Spin Crossover in PbTiO-Based Perovskites.

The discovery of unusual negative thermal expansion (NTE) provides the opportunity to control the common but much desired property of thermal expansion, which is valuable not only in scientific interests but also in practical applications. However, most of the available NTE materials are limited to a narrow temperature range, and the NTE effect is generally weakened by various modifications. Here, we report an enhanced NTE effect that occurs over a wide temperature range , and this NTE effect is accompanied by an abnormal enhanced tetragonality, a large spontaneous polarization, and a G-type antiferromagnetic ordering in the present perovskite-type ferroelectric of (1-)PbTiO-BiCoO.

Tunable Thermal Expansion from Negative, Zero, to Positive in Cubic Prussian Blue Analogues of GaFe(CN).

The achievement of controlling thermal expansion is important for open-framework structures. The present work proposes a feasible way to adjust the coefficient of thermal expansion continuously from negative to positive via inserting guest Na ions or HO molecules into a GaFe(CN) framework. The guest ions or molecules have an intense dampening effect on the transverse vibrations of CN atoms in the -Ga-N≡C-Fe- linkage, especially for the N atoms.

Low-Frequency Phonon Driven Negative Thermal Expansion in Cubic GaFe(CN) Prussian Blue Analogues.

The understanding of the negative thermal expansion (NTE) mechanism is vital not only for the development of new NTE compounds but also for effectively controlling thermal expansion. Here, we report an interesting isotropic NTE property in cubic GaFe(CN) Prussian blue analogues (α = -3.95 × 10 K, 100-475 K), which is a new example to understand the complex NTE mechanism.

Localized Symmetry Breaking for Tuning Thermal Expansion in ScF Nanoscale Frameworks.

The local symmetry, beyond the averaged crystallographic structure, tends to bring unusual performances. Negative thermal expansion is a peculiar physical property of solids. Here, we report the delicate design of the localized symmetry breaking to achieve controllable thermal expansion in ScF nanoscale frameworks.

Isotropic Zero Thermal Expansion and Local Vibrational Dynamics in (Sc,Fe)F.

Scandium fluoride (ScF) exhibits a pronounced negative thermal expansion (NTE), which can be suppressed and ultimately transformed into an isotropic zero thermal expansion (ZTE) by partially substituting Sc with Fe in (ScFe)F (Fe20). The latter displays a rather small coefficient of thermal expansion of -0.17 × 10/K from 300 to 700 K.

Switching Between Giant Positive and Negative Thermal Expansions of a YFe(CN) -based Prussian Blue Analogue Induced by Guest Species.

The control of thermal expansion of solid compounds is intriguing but remains challenging. The effect of guests on the thermal expansion of open-framework structures was investigated. Notably, the presence of guest ions (K ) and molecules (H O) can substantially switch thermal expansion of YFe(CN) from negative (α =-33.

Tunable thermal expansion in framework materials through redox intercalation.

Thermal expansion properties of solids are of fundamental interest and control of thermal expansion is important for practical applications but can be difficult to achieve. Many framework-type materials show negative thermal expansion when internal cages are empty but positive thermal expansion when additional atoms or molecules fill internal voids present. Here we show that redox intercalation offers an effective method to control thermal expansion from positive to zero to negative by insertion of Li ions into the simple negative thermal expansion framework material ScF, doped with 10% Fe to enable reduction.

Thermal and magnetic anomalies of α-iron: an exploration by extended x-ray absorption fine structure spectroscopy and synchrotron x-ray diffraction.

The local structure and dynamics of α-iron have been investigated by extended x-ray absorption fine structure (EXAFS) spectroscopy and x-ray diffraction (XRD) in order to shed light on some thermal and magnetic anomalies observed in the last decades. The quantitative EXAFS analysis of the first two coordination shells reveals a peculiar local vibrational dynamics of α-iron: the second neighbor distance exhibits anharmonicity and vibrational anisotropy larger than the first neighbor distance. We search for possible distortions of the bcc structure to justify the unexplained magnetostriction anomalies of α-iron and provide a value for the maximum dislocation of the central Fe atom.

New Insights into the Negative Thermal Expansion: Direct Experimental Evidence for the "Guitar-String" Effect in Cubic ScF3.

The understanding of the negative thermal expansion (NTE) mechanism remains challenging but critical for the development of NTE materials. This study sheds light on NTE of ScF3, one of the most outstanding materials with NTE. The local dynamics of ScF3 has been investigated by a combined analysis of synchrotron-based X-ray total scattering, extended X-ray absorption fine structure, and neutron powder diffraction.