Temperature Dependence of Raman Spectra of Cuprous Halides

Fukumoto, T.; Nakashima, S.; Tabuchi, K.; Mitsuishi, Akiyoshi

doi:10.1002/pssb.2220730134

Cited by 31 publications

(12 citation statements)

References 26 publications

(5 reference statements)

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“…For CuBr, the formation energy of the Cu 4 center is calculated to be nearly zero ͑0.0 6 0.05 eV͒, while for CuI, Cu 4 is found to be unstable. These results are consistent with experimental observations that the anomalous TO͑b͒ phonon mode in CuBr is seen at temperatures above 80 K [2,8], indicating a low energy metastable state, but that for CuI no anomalous phonon mode is seen [7,8]. The results are also consistent with a smaller (35%) deviation of the bulk modulus in CuBr from its expected value (as compared to 40% in CuCl) and the closeness of the measured and theoretical values for CuI [12,25,26].…”

supporting

confidence: 90%

“…Among the cuprous halides CuCl is the most puzzling and exhibits the greatest number of anomalies. Infrared and Raman experiments show that the phonon spectrum is highly unusual in that two distinct sets of TO and LO phonon modes [2][3][4][5][6][7][8][9][10] are seen (even at temperatures as low as 2 K) where only one set is expected [11]. The Lyddane-Sachs-Teller relation is not obeyed, unless both sets of phonons are taken into account [2,3].…”

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confidence: 99%

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Ground State Structural Anomalies in Cuprous Halides: CuCl

Park¹,

Chadi²

1996

Phys. Rev. Lett.

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We have examined structural instabilities and elastic anomalies in CuCl via first-principles calculations and find that its crystal structure is not ideal zinc blende but that correlated displacements of groups of four Cu atoms lead to a more stable configuration. About 20% of the Cu atoms are estimated to be affected. The Cu-Cu distance in the Cu 4 complex shrinks from 3.82 to 2.72 Å, close to that of metallic Cu. The energetics of defect formation are examined also for CuBr and CuI. PACS numbers: 61.50.Ah, 61.66.Fn, 61.72.Ji, 62.20.Dc Cuprous halides are the most ionic crystals with a zinc blende lattice structure. Their ionicities are near the critical threshold above which cubic binary compounds prefer either the NaCl or the CsCl structure [1]. Among the cuprous halides CuCl is the most puzzling and exhibits the greatest number of anomalies. Infrared and Raman experiments show that the phonon spectrum is highly unusual in that two distinct sets of TO and LO phonon modes [2-10] are seen (even at temperatures as low as 2 K) where only one set is expected [11]. The Lyddane-Sachs-Teller relation is not obeyed, unless both sets of phonons are taken into account [2,3]. Another anomaly first pointed out by Martin [12] is that in comparison with other zinc blende compounds the values of the bulk and shear moduli for CuCl deviate strongly from a simple d 24 scaling with bond length. In particular, the bulk modulus of CuCl is only 60% as large as its expected value.It is well known that CuCl is a superionic material at temperatures above about 450 ± C. At lower temperatures, e.g., room temperature, x-ray and neutron diffraction studies show that CuCl is structurally disordered [5,13,14] with the Cu ions having large displacements away from their tetrahedral sites. Several models [3][4][5][6]13,15] have been suggested to explain the phonon anomalies and disorder in CuCl. Vardeny and Brafman [6] proposed the existence of low energy secondary minima along the four ͓111͔ antibonding directions for Cu. The model received strong support from the first-principles calculations of Wei, Zhang, and Zunger who verified the existence of such minima with a formation energy of 0.1 eV [16].The ͑111͒ soft modes can manifest themselves in two different ways. The displaced Cu atoms can occupy the various ͑111͒ minima randomly, giving a statistically disordered distribution; or if the energy barriers are small (as indicated by the calculations), the potential experienced by a Cu ion would be strongly anharmonic and the Cu atoms would sample the four minima dynamically [6,13]. Most experimental data on CuCl have been interpreted in terms of either the statically disordered or the anharmonic model. Schreurs, Mueller, and Schwartz [14] pointed out many years ago that the two models could be ex-perimentally distinguished via neutron scattering experiments. They suggested that for the anharmonic model all diffuse scattering would be inelastic while for the disordered model there would be an elastic component. The results of their experime...

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supporting

confidence: 90%

mentioning

confidence: 99%

Ground State Structural Anomalies in Cuprous Halides: CuCl

Park¹,

Chadi²

1996

Phys. Rev. Lett.

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“…The DFPT phonon dispersion of CuI is shown in Figure 3a and shows good agreement with the experimental frequencies reported in the literature. 84,85 The minor disparity, such as for the LO-TO splitting, may be attributed to the challenge of precisely capturing the dielectric constants in CuI, as discussed in the next section. This plot is accompanied by the corresponding spectral decomposition of the hole scattering rates at different T (Figure 3b), and shows that the highfrequency longitudinal optical mode T 2 (LO) is the main contributor to the e−ph scattering in CuI.…”

Section: Resultsmentioning

confidence: 99%

Limits to Hole Mobility and Doping in Copper Iodide

Willis,

Claes,

Zhou

et al. 2023

Chem. Mater.

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Over one hundred years have passed since the discovery of the p-type transparent conducting material copper iodide, predating the concept of the “electron–hole” itself. Supercentenarian status notwithstanding, little is understood about the charge transport mechanisms in CuI. Herein, a variety of modeling techniques are used to investigate the charge transport properties of CuI, and limitations to the hole mobility over experimentally achievable carrier concentrations are discussed. Poor dielectric response is responsible for extensive scattering from ionized impurities at degenerately doped carrier concentrations, while phonon scattering is found to dominate at lower carrier concentrations. A phonon-limited hole mobility of 162 cm2 V–1 s–1 is predicted at room temperature. The simulated charge transport properties for CuI are compared to existing experimental data, and the implications for future device performance are discussed. In addition to charge transport calculations, the defect chemistry of CuI is investigated with hybrid functionals, revealing that reasonably localized holes from the copper vacancy are the predominant source of charge carriers. The chalcogens S and Se are investigated as extrinsic dopants, where it is found that despite relatively low defect formation energies, they are unlikely to act as efficient electron acceptors due to the strong localization of holes and subsequent deep transition levels.

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“…The lower frequency peak therefore seems to originate from a rather well defined lattice mode. Phonon spectra recorded a t 4.2 K by Fukumoto et al [9] indicate that the situation hardly will be qualitatively different at very low temperatures unless the low frequency peak loses its IR-activity which would imply a phase transition.…”

Section: Resultsmentioning

confidence: 98%

The origin of the anomalous TO‐doublet in cubic CuCl studied by light scattering

Fukushi

Nippus

Claus

1978

Physica Status Solidi (b)

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Light scattering experiments are performed concerning polaritons associated with the anomalous TO-doublet in CuCl. A quantitative description of the dispersion behaviour, recorded a t liquid N, temperature, may be obtained by taking into account coupling of the fundamental zone centered TO-phonon with second order modes due to two van Hove singularities. This description is in good agreement with recent calculations of the two-phonon density of states in CuCl. Eswerden Lichtstreuexperimente an Polaritonen, die mit dem anomalen TO-Dublett in CuCl verknupft sind, durchgefuhrt. Eine quantitative Beschreibung des Dispersionsverhaltens, das bei der Temperatur des flussigen Stickstoffs aufgenommen wurde, wird unter Beriicksichtigung der Kopplung des fundamentalen TO-Phonons im Zonenzentrum mit Moden zweiter Ordnung infolge von zwei van Hove-Singularititen erhalten. Diese Beschreibung ist in guter ubereinstimmung mit kiirzlichen Berechnungen der Zwei-Phononenzustandsdichte in CuCI. 1) Schellingstr. 4, 8000 Munchen 40, BRD.

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Temperature Dependence of Raman Spectra of Cuprous Halides

Cited by 31 publications

References 26 publications

Ground State Structural Anomalies in Cuprous Halides: CuCl

Ground State Structural Anomalies in Cuprous Halides: CuCl

Limits to Hole Mobility and Doping in Copper Iodide

The origin of the anomalous TO‐doublet in cubic CuCl studied by light scattering

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