Temperature-induced valence instability in the charge-transfer crystal TMB-TCNQ

Nicola Castagnetti, Gabriele Kociok-Kohn, Enrico Da Como, Alberto Girlando

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

The occurrence of so-called temperature-induced neutral-ionic transitions (TINIT) in mixed-stack charge-transfer crystals is quite rare. Here we reinvestigate one of the crystals which has been claimed to undergo such a transition, 3,3′,5,5′-tetramethylbenzidine-tetracyanoquinodimethane (TMB-TCNQ). Extensive optical data allow us to conclude that the transition should be classified as a valence instability, and not as a "true" TINIT, as the ∼0.5 neutral-ionic borderline is not crossed. The ionicity ±, or average charge at the molecular sites, indeed changes very little at the transition, from about 0.3 to about 0.4, and is accompanied by stack dimerization. The transition is first order with large hysteresis, and the crystal may crack or break. For this reason we have been unable to collect x-ray structural data on the low-temperature phase, but with the help of semiempirical calculations we are able to assess a plausible scenario for this peculiar phase transition and its mechanism.

LanguageEnglish
Article number024101
JournalPhysical Review B : Condensed Matter and Materials Physics
Volume95
Issue number2
DOIs
StatusPublished - 3 Jan 2017

Fingerprint

Charge transfer
charge transfer
valence
Crystals
crystals
Dimerization
Temperature
temperature
Hysteresis
Phase transitions
Cracks
X rays
dimerization
tetracyanoquinodimethane
cracks
hysteresis
occurrences
x rays
3,3',5,5'-tetramethylbenzidine

Cite this

Temperature-induced valence instability in the charge-transfer crystal TMB-TCNQ. / Castagnetti, Nicola; Kociok-Kohn, Gabriele; Da Como, Enrico; Girlando, Alberto.

In: Physical Review B : Condensed Matter and Materials Physics, Vol. 95, No. 2, 024101, 03.01.2017.

Research output: Contribution to journalArticle

@article{257a2ed27c0249f5af871935c7aed6a8,
title = "Temperature-induced valence instability in the charge-transfer crystal TMB-TCNQ",
abstract = "The occurrence of so-called temperature-induced neutral-ionic transitions (TINIT) in mixed-stack charge-transfer crystals is quite rare. Here we reinvestigate one of the crystals which has been claimed to undergo such a transition, 3,3′,5,5′-tetramethylbenzidine-tetracyanoquinodimethane (TMB-TCNQ). Extensive optical data allow us to conclude that the transition should be classified as a valence instability, and not as a {"}true{"} TINIT, as the ∼0.5 neutral-ionic borderline is not crossed. The ionicity ±, or average charge at the molecular sites, indeed changes very little at the transition, from about 0.3 to about 0.4, and is accompanied by stack dimerization. The transition is first order with large hysteresis, and the crystal may crack or break. For this reason we have been unable to collect x-ray structural data on the low-temperature phase, but with the help of semiempirical calculations we are able to assess a plausible scenario for this peculiar phase transition and its mechanism.",
author = "Nicola Castagnetti and Gabriele Kociok-Kohn and {Da Como}, Enrico and Alberto Girlando",
year = "2017",
month = "1",
day = "3",
doi = "10.1103/PhysRevB.95.024101",
language = "English",
volume = "95",
journal = "Physical Review B : Condensed Matter and Materials Physics",
issn = "1098-0121",
publisher = "American Physical Society",
number = "2",

}

TY - JOUR

T1 - Temperature-induced valence instability in the charge-transfer crystal TMB-TCNQ

AU - Castagnetti, Nicola

AU - Kociok-Kohn, Gabriele

AU - Da Como, Enrico

AU - Girlando, Alberto

PY - 2017/1/3

Y1 - 2017/1/3

N2 - The occurrence of so-called temperature-induced neutral-ionic transitions (TINIT) in mixed-stack charge-transfer crystals is quite rare. Here we reinvestigate one of the crystals which has been claimed to undergo such a transition, 3,3′,5,5′-tetramethylbenzidine-tetracyanoquinodimethane (TMB-TCNQ). Extensive optical data allow us to conclude that the transition should be classified as a valence instability, and not as a "true" TINIT, as the ∼0.5 neutral-ionic borderline is not crossed. The ionicity ±, or average charge at the molecular sites, indeed changes very little at the transition, from about 0.3 to about 0.4, and is accompanied by stack dimerization. The transition is first order with large hysteresis, and the crystal may crack or break. For this reason we have been unable to collect x-ray structural data on the low-temperature phase, but with the help of semiempirical calculations we are able to assess a plausible scenario for this peculiar phase transition and its mechanism.

AB - The occurrence of so-called temperature-induced neutral-ionic transitions (TINIT) in mixed-stack charge-transfer crystals is quite rare. Here we reinvestigate one of the crystals which has been claimed to undergo such a transition, 3,3′,5,5′-tetramethylbenzidine-tetracyanoquinodimethane (TMB-TCNQ). Extensive optical data allow us to conclude that the transition should be classified as a valence instability, and not as a "true" TINIT, as the ∼0.5 neutral-ionic borderline is not crossed. The ionicity ±, or average charge at the molecular sites, indeed changes very little at the transition, from about 0.3 to about 0.4, and is accompanied by stack dimerization. The transition is first order with large hysteresis, and the crystal may crack or break. For this reason we have been unable to collect x-ray structural data on the low-temperature phase, but with the help of semiempirical calculations we are able to assess a plausible scenario for this peculiar phase transition and its mechanism.

UR - http://www.scopus.com/inward/record.url?scp=85010408116&partnerID=8YFLogxK

UR - http://dx.doi.org/10.1103/PhysRevB.95.024101

U2 - 10.1103/PhysRevB.95.024101

DO - 10.1103/PhysRevB.95.024101

M3 - Article

VL - 95

JO - Physical Review B : Condensed Matter and Materials Physics

T2 - Physical Review B : Condensed Matter and Materials Physics

JF - Physical Review B : Condensed Matter and Materials Physics

SN - 1098-0121

IS - 2

M1 - 024101

ER -