The joint effect of elasticity, interaction energy and entropy on behavior of pressure- and temperature-induced electronic bistability in a family of two-dimensional Hofman-like coordination polymers

Abstract

A comprehensive study of the temperature and pressure-induced spin transition and the change of the physical properties of the 2D Hofmann-type compounds [Fe(Fpz)2M(CN)4] (M = Pd, Ni; Fpz = F-pyrazine)...

Pressure-Induced Mixed States Caused by Spin-Elastic Interactions during First-Order Spin Phase Transition in Spin Crossover Compounds

“…The difference between these values is small and depends on the difference in compressibility of these compounds in high-spin and low-spin states. Using these values Δ p κ , the relative change in the volume δ HS (equal to 0.0237 for Fe–Pt and 0.022 for Fe–Pd) obtained from the X-ray measurements in refs and , and the modulus of elasticity in the high-spin state (equal to 7.14 GPa for Fe–Pt and 9.62 GPa for Fe–Pd), we calculated the coefficients α from expression eq , which determines the spin-elastic interactions and the coefficients D from equation eq or eq determining the change of the spin-elastic energy at ST. For Fe–Pt, α = 0.17 GPa, D = 0.31 GPa, and for Fe–Pd, α = 0.21 GPa, D = 0.5 GPa. It can be seen that as the bulk modulus increases, the spin-elastic energy increases.…”

“…Figure a shows four characteristic temperature dependences of the high-spin fraction (γ HS ) of the molecules calculated from temperature-induced spin transition (TIST) measured in ref at various external pressures for Fe–Pt, and Figure b shows the same data for Fe–Pd calculated from the analogical measurements in ref . At ambient pressure, the hysteresis has a rectangular shape, which meets the abrupt conversion between low-spin and high-spin states.…”

“…Temperature dependences of the high-spin fraction of the molecules γ HS at various external pressure measured with temperature rate 1 K/min: (a) for [Fe­(Fpz) 2 Pt­(CN) 4 ] and (b) for [Fe­(Fpz) 2 Pd­(CN) 4 ] …”

“…They have a first-order ST at ambient pressure (156 and 116 K, respectively), which can be changed to room temperature using pressure and allows us to track changes over a wide temperature range. In the presented work, the effect of pressure on the shape of the TIST in both compounds has been investigated by analyzing the temperature dependences of the order parameter under pressure as well as the Raman spectroscopy behavior under pressure performed in refs and . Additionally, temperature dependences of Raman spectra were measured at atmospheric pressure for both compounds.…”

Anomalous Pressure Response of Temperature-Induced Spin Transition and a Pressure-Induced Spin Transition in Two-Dimensional Hofmann Coordination Polymers

“…, with the coefficient k = 3 being the peak intensity ratio of the completely populated HS and LS states. 36,38,51 The evolution of γ HS for Isoq-Pt and Isoq-Pd with pressure is shown in Figure 3d. The γ HS (P) shows that Isoq-Pt undergoes an "abrupt" complete ST in the interval (ΔP(Pt)) ∼0.25 GPa with transition pressure (P 1/2 Pt ) and hysteresis width (ΔP 1/2 Pt ) of ∼0.81 and ∼0.26 GPa, respectively.…”