Colossal electroresistance response accompanied by metal-insulator transition in a mixed-valent vanadate

Abstract

Colossal electroresistance (CER) in manganites, i.e., a large change in electrical resistance under the influence of either an applied electric field or an applied electric current, has often been described as complimentary to the colossal magnetoresistance (CMR) effect. Mixed valent vanadates with active t 2g and empty e g orbitals, unlike manganites, have not naturally been discussed in this context, as double exchange based CMR is not realizable in them. However, presence of coupled spin and orbital degrees of freedom, metal-insulator transition (MIT) accompanied by orbital order-disorder transition, etc., anyway make the vanadates an exciting group of materials. Here we probe a Fe-doped hollandite lead vanadate PbFe 1.75 V 4.25 O 11 (PFVO), which exhibits a clear MIT as a function of temperature. Most importantly, a giant fall in the resistivity, indicative of a CER, as well as a systematic shift in the MIT towards higher temperature are observed as a function of applied electric current. Detailed structural, magnetic, thermodynamic and transport studies point towards a complex interplay between orbital order/disorder effect, MIT and double exchange in this system.

Preferred orientation in polycrystalline colossal electroresistive hollandite PbFexV6‐xO11

“…Accordingly, temperature dependent transport property measurements have been carried out on an oriented pellet in the directions parallel and perpendicular to the pellet surface which is similar to making measurements on a single crystal parallel and perpendicular to the a−b plane, respectively. Clearly, at every temperature the resistivity appears higher along the c-direction which is consistent with our previous report 12 . It was discussed earlier 12 that presence of intervening Fe 3+ (3d 5 ) ions would restrict the electronic conduction along the cdirection while the conduction will be mostly expressed in the a−b plane (see Figure 4A,B).…”

“…Clearly, at every temperature the resistivity appears higher along the c-direction which is consistent with our previous report 12 . It was discussed earlier 12 that presence of intervening Fe 3+ (3d 5 ) ions would restrict the electronic conduction along the cdirection while the conduction will be mostly expressed in the a−b plane (see Figure 4A,B). Moreover, the onset of the step-wise transition from the high resistive to the low resistive state due to subtle structural changes is also going to be manifested differently along different crystallographic directions which is exactly what is observed here.…”

“…Synchrotron X-ray diffraction measurements on pure polycrystalline PbFe 1.75 V 4.25 O 11 (PFVO-175) samples were performed using a spinning capillary sample mount at low temperature as well as at 300 K by Saha et al 12 and Rietveld refinement of the same were carried out by considering the P6 3 mc space group using the Fullprof software (see Figure 1A,B). However, when the powder PFVO-175 sample is placed in a flat-plate single crystal sample mount using the front-loading (FL) technique (polycrystalline powder placed in a sample mount pressed by a glass slide, the result shown in Figure 1C) and the Rietveld refinement are attempted using the same space group, it is observed that there are severe mismatches between the experimental and calculated relative intensities of few of the d hkl peaks.…”

“…F I G U R E 3 X-ray powder diffraction (light green circle) and Rietveld refinement fitted line (dark green line) and the difference of observed and fitted data (olive line) from pressed PFVO-175 sample at 300K (A) without considering the preferred orientation and (B) considering preferred orientation along (00l) pressed. Therefore, it is evident that the platy habit of the grains of these polycrystalline hollandites are easily susceptible to preferred orientation and should therefore be carefully handled, especially in the context of structure and Fe 3+ (3d 5 ) ions, along with a M(4) trigonal bipyramid consisting of Fe 3+ , connect these planes along the c-direction 12 . Accordingly, temperature dependent transport property measurements have been carried out on an oriented pellet in the directions parallel and perpendicular to the pellet surface which is similar to making measurements on a single crystal parallel and perpendicular to the a−b plane, respectively.…”

“…They were pelletized and sealed in an evacuated quartz tube after wrapping the pellet in a platinum foil (purity 99.95%). The mixtures with doping of x = 1, 1.25, 1.5, 1.75 were annealed in 1198 K, 1173 K, 1148 K, and 1073 K, respectively, for 72 h and then quenched to room temperature 11,12,13 . The purity of the compounds were checked in a Rigaku SmartLab X-Ray Diffractometer with Cu K α (λ = 1.5406 Å) X-ray source, using a flat-plate sample mounting system under Bragg-Brentano geometry.…”