1. Measurement of DC resistivity of new quasi-one-dimensional conducting platinate COLLABORATORS: R. Ian Leatherbury and Ozarfar Gafarov Department of Physics, University of South Alabama A. P. Weber, L. Pham, and R. E. Sykora Department of Chemistry, University of South Alabama A. Khan Department of Electrical and Computer Engineering, University of South Alabama FUNDING: National Science Foundation (NSF) – Research at Undergraduate Institutions University of South Alabama Jessica A. Alexander Undergraduate student Albert A. Gapud P.I. University of South Alabama Department of Physics Mobile, Alabama

2. Measurement of DC resistivity of new quasi-one-dimensional conducting platinate COLLABORATORS: R. Ian Leatherbury and Ozarfar Gafarov Department of Physics, University of South Alabama A. P. Weber, L. Pham, and R. E. Sykora Department of Chemistry, University of South Alabama A. Khan Department of Electrical and Computer Engineering, University of South Alabama FUNDING: National Science Foundation (NSF) – Research at Undergraduate Institutions University of South Alabama Jessica A. Alexander Undergraduate student Albert A. Gapud P.I. University of South Alabama Department of Physics Mobile, Alabama

3. Quasi-One-Dimensional Conductors (Q1D) Restricted geometry: current confined to chain of metal ions/atoms Peierls Transition: from conductor to insulator, due to lattice distortion – New periodicity, a --> 2a – corresponds to k = 2k F – Elastic energy balanced by coulomb interaction – energy gap at k || = k F from Gruner, Reviews of Modern Physics, Vol. 60, No. 4, Oct 1988

4. Q1D platinates, KCP Platinates: parallel chains of Pt along crystal symmetry axis K 2 Pt(CN) 4 Br 0.3 3. H 2 0 aka “KCP” extensively studied (1970s) Each Pt chain ringed by 4 CN Adjacent Pt planes rotated 45o Pt-Pt spacing: Longitudinal – along chain: 2.89 Å Transverse – between chains: 9.88 Å 4 H 2 O rings each Pt-CN plane K, Br separate Pt-CN-H 2 O complexes From: Toombs, Physics Reports 40, No. 3(1978)181.

5. Pt CN Cs 4 [Pt(CN) 4 ](CF 3 SO 3 ) 2 aka “TCP” Pt-CN complexes: like KCP Pt-Pt spacing (room temp): – Longitudinal: 3.03 Å (5% longer) – Transverse: 13.61 Å (38% farther) Cs instead of H 2 O Triflates (CF 3 SO 3 - ) instead of K, Br New Q1D platinate: TCP

6. Our Study: DC resistivity of TCP KCP: Conductivity vs T High anisotropy -Transverse ~ 10 5 lower Peierls transition temperature not observed (above room temperature?): already semiconducting/insulating DC ρ(T): increases with cooling From: Toombs, Physics Reports 40, No. 3(1978)181. OBJECTIVE: TCP: Measure ρ(T) ; compare to KCP Effect of longer Pt-Pt spacings = ?

7. precipitate from solution bright metallic red in color small dimensions: – approximately 2-5 mm in length – less than 1 mm wide – less than 0.5 mm thick extremely fragile – a “Krogmann salt” – must be handled indirectly opted for 2-point contact – Contact R << sample R (contacts tested on Cu dummy) Experimental Details: TCP samples

8. Experimental Details: Mounting Problem: Contact with Sample Solution: Sputtered Au hydroscopic: liquid layer on the surface of the TCP – Carbon paint contact: V increase (charging) – Sputtered Au : enough energy for better contact for carbon paint, prevent moisture masking: sample set in the folds of teflon tape; covered w/ brass strip Better contact: V stable (no charging) Samples Prepared for DC Sputtering teflon tape brass foil TCP sample glass slide tape DC Sputtering System

9. Experimental Details: Mounting m Problem: Thermal Shock Various mounts attempted Initial, anchored mount: sapphire coated w/ Au, sample across gap in Au Sample breakage w/ thermal cycling Thermal expansion/contraction coefficient significant Freund, J. Appl. Cryst. 7, 631 (1974) “Friction mount”: sample across foils on vacuum grease Stability + more freedom for thermal expansion/contraction “Spring mount”: sample leads are slack Stability + more freedom for thermal expansion/contraction Sample on teflon-tape surface Pt wire C-painted “dumbbells”

10. Experimental Details: Mounting m Problem: Thermal Shock Solution: “Guitar Mount” with Pt Wires G10 tape sample platinum wire Initial, anchored mount: -Sample breakage -Disjointed R(T) from Coleman, Review of Scientific Instruments – August 1975 G10 base w/ a gap in the middle Suspension wires – laid each wire across G10 gap – separation distance tailored to sample – taped to the G10 at each side of the gap – slack – used copper wire at first; switched to platinum wires for less mass & tension sample across the wires, C paint contact soldered wires to fixed current leads SLOW cooling and warming Max 3 K/min

11. Results: CRITERIA: – Smooth R(T) good contact, no thermal shock – Reversible with temperature TCP: more insulating than KCP – R ~ 10 7 Ω – σ || ~ 10 -5 (Ωcm) -1 Compared to KCP: Average ~ 10 5 times smaller T variation ~ 10 3 less Anomalous peak in R(T) – T > 200 K: monotonic increase w/ cooling, like KCP – T ~ 170 K: saturate, then decrease TCP13Guitar

12. Further study: not like KCP Structural transition below 200 K: towards KCP- like spacing? Cryogenic XRD shows lattice contraction w/ cooling – 210 K: Longitudinal: decrease 1.15% Transverse: decrease 0.35% – (Lower temperatures: ongoing) – Peak: Effect dominated by 3D ordering (inter-chain) ? T > 200 K: Different orbital sharing for Pt-Pt? SQUID magnetometry: no response Want: specific heat, pressure effects, … May be consistent with results of NMR study (next talk)

13. Spare slides follow

14. Experimental Details: DC transport Settings: apply current, measure voltage – set based on room temperature resistance of the sample – Both directions, to eliminate offsets temperature control – Indirect cool w/ liquid nitrogen – Slow cool / warm < 3 K/min 9-T, 60-A DC Transport System at USA-Physics Dewar, minimum temp = 4.2 K meters and power supply computer and interface student

15. Results: Figure of the Friction Mount Intermediate between “guitar” and anchored: residual restriction to thermal contraction/expansion – base : molded G10 – four brass foil strips, each mounted on vacuum grease – Sample mounted on inner foils, C paint – Inner foils connected to outer foils w/ slack Pt wire, C paint – current leads: copper wires connected to outer foils w/ C paint “Friction Mount”: showed effect of compression/tension? sample carbon paint vacuum grease copper wire G10 platinum wire brass foils

16. Results: Warming (red): thermal expansion may be suppressed by friction mount: equivalent to longitudinal compression compression may be responsible for earlier thermal shock breakages mount: compression may be weak enough to preserve sample but significant enough to affect electrical properties should increase with T KCP R(T) decreases with compression. TCP : reverse result! 170 K: dip instead of peak <170 K: like KCP >170 K: compression increases R? TCP6Friction m “Friction Mount”: showed effect of compression/tension?