Abstract
The negative thermal expansion material potassium cadmium dicyanoargentate, KCd[Ag(CN)2]3, is studied at high pressure using a combination of X-ray single-crystal diffraction, X-ray powder diffraction, infrared and Raman spectroscopy, and density functional theory calculations. In common with the isostructural manganese analogue, KMn[Ag(CN)2]3, this material is shown to exhibit very strong negative linear compressibility (NLC) in the crystallographic c direction due to structure hinging. We find increased structural flexibility results in enhanced NLC and NTE properties, but this also leads to two pressure-induced phase transitions—to very large unit cells involving octahedral tilting and shearing of the structure—below 2 GPa. The presence of potassium cations has an important effect on the mechanical and thermodynamic properties of this family, while the chemical versatility demonstrated here is of considerable interest to tune unusual mechanical properties for application.
Highlights
IntroductionMaterials where external stimuli induces an anomalous response, such as expansion upon cooling (negative thermal expansion, NTE1−3) or on application of hydrostatic pressure (negative linear compressibility, NLC4,5), have recently received considerable attention
Materials where external stimuli induces an anomalous response, such as expansion upon cooling or on application of hydrostatic pressure, have recently received considerable attention
We identify two main phase transitions up to 4 GPa and solve the distorted structures based on powder and single-crystal X-ray diffraction
Summary
Materials where external stimuli induces an anomalous response, such as expansion upon cooling (negative thermal expansion, NTE1−3) or on application of hydrostatic pressure (negative linear compressibility, NLC4,5), have recently received considerable attention. These materials that “break the rules” as a result of specific, and rare, elastic anomalies[6−8] are curious from a fundamental point of view but might be revolutionary for a range of technologies including interferometric pressure sensors, pressure-controlled or pressure-sensitive electronic devices, and smart actuation.[2,4,9−11] The ability to design materials with unusual properties is a key focus of the field: can we understand these elastic anomalies so that we can tune the magnitude and/or range of negative responses?.
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