Showing papers on "Molecular solid published in 1973"
TL;DR: In this paper, the first paraferroelectric transition was observed in a pure molecular solid (without H bonds) without H bonds using x-ray diffraction, calorimetric and dielectric measurements and direct optical observation of domain-wall displacement under an applied electric field.
Abstract: We report here evidence for the first paraferroelectric transition observed in a pure molecular solid (without H bonds); we present results from x-ray diffraction, calorimetric and dielectric measurements, and direct optical observation of domain-wall displacement under an applied electric field.
54 citations
TL;DR: In this article, the authors proposed the Frenkel tight-binding model to describe the lower energy states of molecular solids, i.e., ion pair states in which an electron and hole are localized on neighboring lattice sites.
Abstract: The electronic states generally characterize solids as insulators, semiconductors, or metals,1 but in some respects organic molecular crystals are an exception to ths scheme. To describe the lower energy states of these solids, the concepts of a valence band and a conduction band are not very useful because the electrons are hghly localized. These states are described better by the Frenkel tight-binding model in which molecular states are the progenitors of crystal states.2 Generally at higher energies, crystal states not present in the free molecule are expected.3 These states, the ionic states, consist of an electron and an ionized molecule. Such states may be similar to the exciton and conducting states of other solids or may be somewhat unique to the molecular solid, e.g., ion pair states in which an electron and hole are localized on neighboring lattice sites. In spite of the apparent importance of the ionic states in understanding electron and energy transfer phenomena in molecular aggregat...
35 citations
TL;DR: In this article, a new method to identify the nature of vibrations in molecular crystals as external or internal is proposed, which is supported by experimental isotopic mixed crystal studies of many molecular crystals.
22 citations
TL;DR: In this article, the trap depths are the same for all three rotations in benzene mixed crystals, and a one-to-one correspondence between the mixed crystal absorption and the pure crystal absortion is shown.
Abstract: Raman spectra of mixed crystals of benezene‐h6 and benzene‐d6 have been studied throughout the whole concentration range (0%–100%). They are discussed in the virtual crystal limit, suitable for small trap depths. It is shown that within this limit: (1) All the phonons are delocalized in mixed crystals; (2) k‐designation is still valid, and (3) no appreciable broadening is expected in mixed crystals. In particular, because the trap depths are the same for all three rotations in benzene mixed crystals, it is further inferred that: (1) There is a one‐to‐one correspondence between the mixed crystal absorption and the pure crystal absortion; (2) spectral line positions depend on the concentration linearly; and (3) the normal coordinates in the mass (or moment of inertia)‐weighted coordinates remain unchanged from benzene‐h6 to mixed crystals to benzene‐d6. All these conclusions are supported by the experimental data. More general cases, where trap depths are different for different degrees of freedom, are also...
21 citations
01 Jan 1973
TL;DR: In this paper, the authors discuss a class of organic solids in which arise questions of fundamental solid state physics interest as well as having potential technological applications, and the main purpose of these lectures is to discuss the theoretical aspects of the electronic properties of the systems under consideration.
Abstract: The purposes of these lectures is to discuss a class of organic solids in which arise questions of fundamental solid state physics interest as well as having potential technological applications. Although our focus will be on the solid state physics aspects of the electronic properties of the systems under consideration, the general field of study involves a strong overlap between physics and chemistry.
4 citations
TL;DR: In this article, the spin-phonon interaction in molecular crystals is discussed in terms of the direct process single phonon absorption by the paramagnetic spin system, and it is estimated that sufficient acoustic power densities may be produced to observe acoustic paramagnetic resonance by optical detection methods.
3 citations
2 citations
1 citations
TL;DR: In this article, it is shown that the self-energy due to disorder is in general non-diagonal when bands with different trap depths are interacting, and a useful products rule is derived that is independent of the intermolecular potential provided it is the same for both components.
1 citations
IBM1
TL;DR: In this article, the electrical and optical properties of a photo-sensitive polyvinyl carbazole (PVCZ) and 2,4,7-trinitrofluorenone (TNF) were investigated.
Abstract: Our interest in these calculations is based on our desire to understand the properties of a photosensitive polymer. The organic polymer film consisting of a 1:1 monomer molar ratio mixture of poly-n-vinylcarbazole (PVCZ) and 2,4,7-trinitrofluorenone (TNF) is a sensitive organic photoconductor currently being used in the IBM electrophotographic copier. In this laboratory we are presently investigating the electrical and optical properties of this and related materials. The carbazole monomer unit and the TNF molecule (see Figs. 1 and 2) are known to form charge transfer complexes about which relatively little is known. But these molecules are mainly responsible for the photosensitivity in the visible region. Our experimental results indicate that optical absorption, photo-generation efficiency of free carriers, and the very small charge carrier mobilities are all strongly field dependent. These results support the description of these materials as disordered molecular solids and we expect that the properties of the basic molecular constituents can be expected to have a relatively direct correlation to the properties of the solid as a whole.
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TL;DR: Clark as discussed by the authors proposed a coordinate polyhedron approach for non-molecular solids, based on the Structures of Non-Molecular Solids (SNS) approach.
Abstract: The Structures of Non-molecular Solids: a Coordinated Polyhedron Approach. By Graham M. Clark. Pp. xii + 365. (Applied Science: London, 1972.) £9.