Pressure Study of the Thermal Spin Transition and the High-Spin → Low-Spin Relaxation in the R3̄ and P1̄ Crystallographic Phases of [Zn1-xFex(ptz)6](BF4)2 Single Crystals (x = 0.1, 0.32, and 1; ptz = 1-n-propyltetrazole)
Pressure Study of the Thermal Spin Transition and the High-Spin → Low-Spin Relaxation in the R3̄ and P1̄ Crystallographic Phases of [Zn1-xFex(ptz)6](BF4)2 Single Crystals (x = 0.1, 0.32, and 1; ptz = 1-n-propyltetrazole)
复制标题
[Zn1-xFex(ptz)6](BF4)2 单晶 (x = 0.1、0.32 和 1) 的 R3̄ 和 P1̄ 晶相中的热自旋跃迁和高自旋 → 低自旋弛豫的压力研究； ptz = 1-正丙基四唑）
DOI：
10.1021/jp972083k
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发表时间：
1997
影响因子：
3.3
通讯作者：
A. Hauser
中科院分区：
文献类型：
--
作者：
J. Jeftić;A. Hauser
在铁（II）自旋交叉化合物[Fe（ptz）6]（BF 4）2中，热自旋转变伴随着在环境压力下表现出Tc↓ = 128 K和Tc↑ = 135 K的滞后的晶体相变[Franke，P.L.; Haasnot，J. G.;楚尔A. P. Inorg. Chim. Acta 1982，59，5]。滞后是由于自旋转变和R → P晶体学相变之间的相互作用，其中大的低自旋部分在低温下稳定P相。在混晶[Zn 1-xFex（ptz）6]（BF 4）2（x = 0.1）中，铁络合物嵌入同晶锌晶格中，晶体相变可由外部压力诱导[Jeftic，J.; Romstedt，H.;豪瑟，A. J.Phys.Chem.Solids1996，57，1743]。因此，P相通过外部压力额外地稳定。描述自旋变化复合物之间的协同效应的相互作用常数Γ对于两个结晶相是不同的。通过对不同压力和P相中铁含量x的一系列过渡曲线的同时拟合，确定了144（8）cm-1的Γ（P）值和29（4）A3的体积差。将这些值与R相的相应值，即170（9）cm-1和26（3）A3的Γ（R）进行比较。令人惊讶的是，尽管Γ（R）小于Γ（P），但Γ（R）大于Γ（P）。在高于80 K的温度下，高自旋→低自旋弛豫是热激活的，而在低于40 K的温度下，发生与温度无关的隧穿。1 kbar的外部压力在两个晶相的隧穿区中以指数方式加速高自旋→低自旋弛豫1个数量级，并且与x无关。在浓缩材料中，由于内部压力的积累，高自旋→低自旋弛豫是自加速的[豪瑟，A.化学物理快报1992，192，65]。合作效应和外压都导致1A 1 → 1 T1吸收带的最大值发生移动。
In the iron(II) spin-crossover compound [Fe(ptz)6](BF4)2, the thermal spin transition is accompanied by a crystallographic phase transition showing a hysteresis with Tc↓ = 128 K and Tc↑ = 135 K at ambient pressure [Franke, P. L.; Haasnot, J. G.; Zuur, A. P. Inorg. Chim. Acta 1982, 59, 5]. The hysteresis is due to an interplay between the spin-transition and the R → P crystallographic phase transition with a large low-spin fraction stabilizing the P phase at low temperatures. In the mixed crystal [Zn1-xFex(ptz)6](BF4)2, x = 0.1, with the iron complexes imbedded into the isomorphous zinc lattice, the crystallographic phase transition can be induced by an external pressure [Jeftic, J.; Romstedt, H.; Hauser, A. J. Phys. Chem. Solids 1996, 57, 1743]. Thus the P phase is additionally stabilized by external pressure. The interaction constant Γ, which describes cooperative effects between the spin-changing complexes, differs for the two crystallographic phases. Values for Γ(P) of 144(8) cm-1 and the volume difference of 29(4) A3 are determined from a simultaneous fit to a series of transition curves for different pressures and iron content x in the P phase. These values are compared to the corresponding values for the R phase, viz. Γ(R) of 170(9) cm-1 and of 26(3) A3. Surprisingly Γ(R) is larger than Γ(P) despite the fact that is smaller than The high-spin → low-spin relaxation at temperatures above 80 K is thermally activated, while below 40 K temperature independent tunnelling takes place. An external pressure of 1 kbar accelerates the high-spin → low-spin relaxation exponentially by 1 order of magnitude in the tunnelling region in both crystallographic phases and regardless of x. In the concentrated material the high-spin → low-spin relaxation is self-accelerating due a buildup of an internal pressure [Hauser, A. Chem. Phys. Lett. 1992, 192, 65]. Both cooperative effects and external pressure result in a shift of the maximum of the 1A1 → 1T1 absorption band.