Nonlinear Electrical Conductivity, Current Oscillation and Its Control in Halogen-Bridged Nickel(III) Compounds - Material Designs and New Physical Properties in MX-and MMX-Chain Compounds - page 85

[Ni(chx n ) 2 Cl]Cl 2

200K

a b

0.2

0.1

0

0 50 100

c

Time(s)

0

50

100

0 100 200 300 400

VoltageV pq (V)

Fig. 6.4 Current and voltage behaviors for [Ni(chxn) 2 Cl]Cl 2 at 200 K [ 11 ]. (a) Currents I s ( filled
dots ) and I b ( broken line ) are plotted versus voltages V pq . The open circles are the I - V
characteristics of the sample without the serial resistor. The current-voltage trajectory in the
current oscillation is also plotted. (b) Temporal profile of the current with and without the external
capacitor. (c) Temporal profile of the voltage V pq with and without the external capacitor

other hand, with the capacitor (black in Fig. 6.3c, d ), the current and voltage do not
reach the stationary point but oscillate. The period is roughly 20 s. The similar
current oscillation can be obtained in Ni-Cl at 200 K shown in Fig. 6.4 [ 11 ]. In
Fig. 6.4a , the I - V property of the sample is shown by open circles. The I - V
properties of the combined resistance of the sample and the serial resistor R s are
shown by filled circles. We obtained the S-shape curve also for Ni-Cl. However,
the obtained S-shape curve for Ni-Cl is elongated in the direction of current. Using
the S-shape properties, we achieved the current oscillation. The temporal profiles
of the current and voltage are shown in Fig. 6.4b, c , respectively. We obtained clear
oscillations. The amplitude of the current is enough large, and the contrast of the
oscillation (on-off ratio in current) is large. On the other hand, the amplitude is
small for voltage. The obtained contrast is small. These contrasts in the amplitude
of the oscillation are dependent on the original NDR properties of the sample. In
Ni-Br, the slope is small in negative resistance region. Therefore, we achieved the
clear S-shape properties in I-V plot (Fig. 6.2a ) for Ni-Br, while the steep slope in
negative resistance region for Ni-Cl leads to an unclear S-shape curve. Resultantly,
the contrast in voltage is small.
The trajectory of the current and V pq is shown in Fig. 6.4a by a solid line, which
indicates that the current and V pq oscillate counterclockwise in the current-voltage
plot. In more detail, after turning on the current, the current increases along the