109AgNMR investigation of atomic motion in the incommensurate and paraelectric phases of proustite(Ag3

High-temperature phase transitions, dielectric relaxation, and ionic mobility of proustite, Ag3AsS3, and pyrargyrite, Ag3SbS3

“…3,4 They found that proustite exhibits anomalous dielectric relaxation under illumination with white light at TϽ305 K: Ј increases anomalously with decreasing temperature. This behavior coincides with the assumption of Subramanian et al 21 proposed in their NMR, where they have found the onset of Ag ϩ diffusion motions at about 240 K just above the broad transition of Yang and Taylor. 4 Unfortunately, Subramanian et al 21 did not state whether or not their experiments were undertaken in darkness or under illumination, as the system is highly influenced in its characteristics by illumination.…”

“…This behavior coincides with the assumption of Subramanian et al 21 proposed in their NMR, where they have found the onset of Ag ϩ diffusion motions at about 240 K just above the broad transition of Yang and Taylor. 4 Unfortunately, Subramanian et al 21 did not state whether or not their experiments were undertaken in darkness or under illumination, as the system is highly influenced in its characteristics by illumination. In darkness, no Debye relaxation is seen by us at TϽ305 K and there was no maximum observed in the dielectric loss function and Љ, 3 as is confirmed in this study.…”

“…They, therefore, hop between multi-well potentials with an activation energy of 0.42 eV ͑calculated from the dependence of the characteristic relaxation time given by the peak in tan ␦ on 1/T for our measured data͒. The onset of this process claimed by Subramanian et al 21 at 240 K could not be confirmed in our investigation in darkness. An explanation for their measurement could be that their diffusion measured below room temperature is a similar characteristic to the onset of the fast ion conduction at 420 K where the number of disordered Ag ϩ slowly increases up to the transition temperature.…”

Magnetic resonance investigations of phase transitions and modulation wave motions in incommensurate solids

“…These observations were attributed to a spatially inhomogeneous electric field gradient (EFG) which fluctuates in time due to the diffusionlike motions of the incommensurate modulation wave between the pinning centers. (A similarly short Hahn-echo decay time has also been observed in other systems, characterized by different fluctuating interactions, e.g., Knight shift [5] and chemical shift [6], and attributed to slow atomic or molecular motions). However, in the case of 'SCl nuclear quadrupole resonance (NQR) in Rb2ZnC14, observations of a rapid Hahn decay with an exponential dependence on r3 does not unambiguously prove the existence of modulation wave motions because of the possibility that these results may simply reflect slow reorientations of the ZnCl4 tetrahedra.…”

Could incommensurability in sulfosalts be more common than thought? The case of meneghinite, CuPb13Sb7S24

“…Incommensurate modulations can also be found among sulfides, tellurides and sulfosalts including bornite (Buseck & Cowley, 1983), pyrrhotite (Li & Franzen, 1996), calaverite (e.g. Schutte & de Boer, 1988;Caracas & Gonze, 2001), sylvanite (Krutzen & Inglesfield, 1990), rickardite (Schutte & de Boer, 1993), muthmannite (Bindi, 2008), proustite (Subramanian et al, 2000), the cylindrite-franckeite series (Evain et al, 2006;Makovicky et al, 2008Makovicky et al, , 2011, lengenbachite (Makovicky & Hyde, 1981;Makovicky et al, 1994), the pearceite-polybasite series (Withers et al, 2008;Bindi et al, 2013), and sartorite (Pring et al, 1993). Among sulfosalts, however, only the incommensurate structures of levyclaudite (Evain et al, 2006) and franckeite (Makovicky et al, 2011) have been studied by means of a multidimensional crystal structure refinement.…”