H. Hild et al., EFFECT OF TENSILE-STRESS ON THE PHASE-TRANSITION IN CU(2,5-DIMETHYL-N,N'-DICYANOQUINONEDIIMINE)(2) - CORRELATION OF CRYSTAL LENGTH AND CONDUCTIVITY, Solid state communications, 101(8), 1997, pp. 563-567
Using a new interferometric mechanical set up, we have measured the el
ongation and the resistance of deuterated Cu(2,5-dimethyldicyanoquinon
ediimine)(2) crystals along the c-direction as functions of temperatur
e. The crystal length l decreases with dl/(l . dT) = 1.1 . 10(-4)/K at
about 300 K to exhibit a minimum at 50 K. Below 50 K, I increases at
further cooling. At the metal-insulator transition detected by a sharp
increase of the resistance R(T) at about 70 K, l(T) reveals a smooth
step exhibiting a hysteresis between the heating and the cooling cycle
as is also observed in R(T). The new setup allowed us to apply tensil
e stress which shifts the phase transition to lower temperatures. A mo
del for the shrinking of the lattice dimension upon localization of th
e charge carriers (disproportion of the mixed valence Cu states) is gi
ven, based on static coulombic repulsion only. Young's modulus was det
ermined for several temperatures. (C)1997 Elsevier Science Ltd.