Electrical conduction in some important copper based superionic solids

Measurement of the thermoelectric power (S) and electrical conductivity () of six superionic solids namely CuI, CuPb₃Br₇, Cu₂HgI₄, Cu₃CdI₅, Cu₃RbCl₄, Cu₇(C₆H₁₂NH₃)Br₈ and Cu₁₆Rb₄I₇Cl₁₃ are reported from 300 K to nearly the melting point of each material. The log T andS againstT ^–1 plots are linear in some temperature ranges with different slopes. For each material they show two distinct regions: one corresponding to superionic (SP) and the other to normal phase (NP). In the superionic phase, Cu⁺ ions are the main entity of charge carrier and an extended lattice gas model explains the transport mechanism fairly well. On the higher temperature side of SP, the other cation in the material starts contributing significantly to. In the normal phase the conduction is mainly due to Frenkel defects (Cu⁺ ions at interstitial sites). The enthalpy for migration and heat of transport of these defects has also been evaluated for CuI, CuPb₃Br₇, Cu₂HgI₄ and Cu₃CdI₅. The formation energy of defects has also been calculated for CuI and Cu₃CdI₅. Normal phase has not been obtained in Cu₃RbCl₄, Cu₇(C₆H₁₂NCH₃)Br₈ and Cu₁₆Rb₄I₇Cl₁₃ as their phase transition temperatures lie below room temperature.     

Electrical conduction in copper phosphate glasses containing nickel or cobalt

A variation in d.c. conductivity and activation energy of 35 mol%CuO-65mol%P₂O₅ glasses is observed as CuO is gradually replaced by NiO or CoO. These results are believed to be due to the change in the redox ratio of the two transition metal oxide glasses, which causes an increase and then a decrease of polaron hopping transitions between the ions of the same element and between the ions of the different transition metal elements.     

Electrical conductivity of single crystal nickel tungstate

Measurements of a.c. and d.c. electrical conductivity in crystals of nickel tungstate, in the temperature range 300 to 1100 K, are presented. NiWO₄ is found to be a semiconductor with a band gap of 2.10 eV. The nature of the electrical conduction is discussed in the light of various conduction models.     

Electrical conduction in manganese molybdate

Electrical conduction in manganese molybdate (MnMoO₄) has been explained on the basis of electrical transport data obtained by measuring electrical conductivity (a.c. and d.c.), thermoelectric power and the dielectric constant of MnMoO₄ in the temperature range 300–1000K. MnMoO₄ has been found to be a semiconductor with the energy gap 3.5 eV. A marked change at ~ 600K occurs due to transition from extrinsic to the intrinsic conduction. Depending upon the electrical transport data, electrical conduction in the extrinsic region has been explained in terms of the small polaron hopping mechanism and in the intrinsic region it has been explained in terms of the localized model of of electrical transport.     

Electrical conduction in quartz powder

Observations have been made on the direct current behaviour of crushed natural quartz at temperatures of the order of 1300 K in order to investigate the effect of applied electric fields on the impurities present in the samples. Migration of the alkaline impurities, leaving an alkali free layer adjacent to the anode, has been detected by analysis of the specimens. It is suggested that the electrical conduction in quartz is due almost entirely to the motion of these impurities. Finally, an estimation of a mean diffusion coefficient for these metals was made and was found to be of the order of 10^–l6m² sec^–1.     

Electrical conduction in non-metallic rare-earth solids

Schematic energy band diagrams for the genesis of charge carriers in non-metallic rare-earth solids have been presented. It has been shown that positions of 4f bands have significant effect on the genesis and nature of charge carriers, their conduction mechanism and magnitude of electrical conductivity () and Seebeck coefficient (S) of the solid. Relevant relations have been given for both and S in different situations. Experimental data on rare-earth sesquioxides (R₂O₃), rare-earth tungstates [R₂(WO₄)₃] and rare-earth molybdates [R₂(MoO₄)₃] in the intrinsic range have been explained as examples for the validity of energy band diagrams.     

Electrical conduction in solution-grown polycarbonate films

The electrical conduction in solution-grown polycarbonate films was studied at different voltages between 1 and 10⁴V as a function of thickness from 25 to 65 μm at a constant temperature of about 385 K and as a function of temperature in the range 328–430 K at a constant thickness of about 50 μm. The results show two distinct regions corresponding to different types of conduction: region I at low or moderate fields where the slope of the current-voltage characteristics is about 2 and region II at high fields where the slope is about 4. The Richardson-Schottky effect was suggested as the dominant mode of conduction at moderate fields whereas at high fields the currents were found to be space charge limited.     

Electrical conduction in light rare-earth tungstates

This paper reports the results of electrical conductivity (σ) and thermoelectric power (H) of light rare-earth tungstates in the temperature range 600–1200K. Holes are the dominant charge carriers over the whole studied temperature range for Nd, Sm and Gd tungstates. However, in the case of La, Ce and Pr tungstates, the conduction is dominated by electrons at lower temperatures, but above 950K in La, 800K in Ce and 950K in Pr the dominant charge carriers become holes. A sharp break and change in the log σ vs 1/T slope occurs in La, Ce and Pr tungstates around the same temperature at which the dominant charge carrier changes from electrons to holes. In the case of Nd, the conductivity anomaly occurs around 1020K without any change in the nature of the charge carrier. The data have been analysed using band theory.     

Electrical conduction in CuWO4 crystals

The d.c. electrical conductivity and thermoelectric power of CuWO₄ have been measured in the temperature range 300 to 700 K on unannealed and annealed single crystals and on polycrystalline pellets. It has been found that CuWO₄ is an n-type semiconductor. Relevant conduction mechanisms appropriate to the regions below and above 455 K are discussed on the basis of the experimental data on activation energy, mobility and carrier concentration.     

Electrical conduction of sodium acetylacetonate

The temperature dependence of DC electrical conductivityσ of sodium acetylacetonate compound Na(ac,ac) is studied for fresh and polarized samples. Both samples show semiconductor behaviour, but the value ofσ for the fresh sample is higher than that of the polarized sample. Three distinct regions are observed in the temperature conductivity curves. The conduction mechanism of each region is discussed. Anomalous conductivity phenomena are observed above 105°C and attributed to unidirectional intermolecular or phase transformation. The results are discussed on the basis of ionic conduction and some conduction parameters such as conduction energyE _c, transport energyE _u, ion mobilityu, free ion densityn, are calculated.