ELECTRICAL RESISTIVITY Four Probe Method Electrical resistivity measurements

ELECTRICAL RESISTIVITY Four Probe Method Electrical resistivity (ρ) measurements are carried out by the standard four-probe method over the temperature 8 -300 K. Four platinum (Pt) electric leads are attached with silver paint/indium soldering on rectangular bar of specimens cut from sintered pellets with uniform cross section, as shown in Figure right side. ρis obtained from ρ= RA/L, where R is resistance, A is area of cross section, and L is length between voltage leads. Schematic diagram of resistivity measurement General Description Closed cycle refrigerator (CCR) systems provide a convenient means of cooling samples to temperatures below 10 K. CCR systems require no liquid nitrogen as a source of cooling. Instead, a closed loop of helium gas is compressed and expanded. The electrical resistivity system include the following components : cold head, gas lines, optional temperature controller, and compressor. Diagram of the Setup of Resistivity Measurement Pump Prepare the sample RMC-Cryosystems Thermometer Sample space System Interconnections CJ-LR 400 GPIB Adapter 7001 Switch System PC AT Program Control Data Output LR-400 Fore-Wire AC Resistance Bridge CTI-Cryogenics (MODEL 22) Experimental Results Electrical resistivity as a function of temperature for La 2 -x. Srx. Cu. O 4 Electrical resistance as a function of temperature for Li. Ti 2 O 4