Optical Absorption by Polarons in Rutile (TiO<sub>2</sub>) Single Crystals

Bogomolov, V. N.; Mirlin, D. N.

doi:10.1002/pssb.19680270144

Cited by 94 publications

(68 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In [ l ] and [3] it was shown that at high temperatures in the frequency region where o ( o ) = const its value approaches the dc conductivity o. This experimental fact strongly supports the interpretation given in [ l ] and [3]. For all other mechanisms of optical transition this coincidence should be accidental.…”

Section: )supporting

confidence: 77%

On the Experimental Observation of Small Polarons in Rutile (TiO₂)

Bogomolov

Firsov

Kudinov

et al. 1969

Physica Status Solidi (b)

Self Cite

View full text Add to dashboard Cite

A careful analysis of certain observations concerning the polaron nature of current carriers in rutile is presented. The criticism of our paper [l] given in [2] is shown to be unfounded.KpuTasecmx a a n i e r a~~f i , Some arguments confirming the polaron nature of current carriers in rutile were given in [l]. I n the two first sections of his paper Klinger [2] enumerates the well-known results of small polaron theory. I n Section 3 (see items 1' to 5') he criticizes the analysis of experimental data on rutile given in [l].We shall prove in this paper that all arguments given in 1' to 5' of [2] are misleading and do not invalidate our conclusions obtained in [l].1.' I n 1' one may read that "at T = const, a('P)(w) N (T N Ni (1 -K ) as well as a@p)(w) IV 0'' l ) , where d i p ) is the absorption coefficient for polarons localized on impurity ions, d S p ) the absorption coefficient for free polarons, Ni the impurity concentration, K the compensation degree, and (T the dc conductivity. It means that free carrier absorption and absorption due t o nonionized impurities are both proportional to (T, and if one takes G to be a measure of concentration it is impossible to distinguish between them a t T = const. Separation of these both types of absorption can be achieved in particular by taking into account their different T-dependence. On page 484 in [2] Klinger also mentions about this possibility. It is very strange indeed that he did not notice that precisely this simple method was used in [l], where it was shown that G ( O ) increases with increasing T (whereas diP)(w) should decrease with increasing T). The simultaneous increase of cr and a(w) with T for 300 O K < T < 600 OK in samples with deeper donor levels is shown in our recent papers [3].2'. I n 2 we read that "for the SP Seebeck coefficient in" pure "samples, y@P) = const should be observed a t T > T, ( 5 100 OK), while the experiment shows this rather a t T 2 300 OK". Herewith Klinger refers to papers [4] to [7].We reproduce Fig. 6 from [7] which clearly shows that y in rutile is independent of T till T = 70 to 100 OK (cf. Fig. 1). Thus the T-dependence of y is just the same as it should be in Klinger's opinion for small polarons. 1)The original text quoted from [2] is put in inverted commas.

show abstract

Section: )supporting

confidence: 77%

On the Experimental Observation of Small Polarons in Rutile (TiO₂)

Bogomolov

Firsov

Kudinov

et al. 1969

Physica Status Solidi (b)

Self Cite

View full text Add to dashboard Cite

show abstract

“…18 The identification of defects in rutile TiO 2 is particularly challenging as the energy scheme of the defect levels may be influenced by polaronic effects. [19][20][21][22][23][24][25][26][27][28][29] First, this makes the theoretical description of defects in rutile TiO 2 exceptionally challenging. 19,24 Second, polaronic effects can also lead to different defects having similar experimental signatures as electrons are trapped at similar Ti sites no matter which defect they actually originate from.…”

Section: Introductionmentioning

confidence: 99%

“…19,20,23,24 This can, for example, be observed in the case of H i : Conductivity, transport, electron paramagnetic resonance, and infrared absorption measurements report on a shallow donor level with thermal transition energies of several meV, 10,11,25,[30][31][32] while absorption data indicate optical transition energies of around 1-2 eV. 8,28,32,33 Another prominent example is V O . Some experiments indicate that V O is a shallow donor in rutile TiO 2 , responsible for the n-type conductivity observed in samples annealed at low oxygen partial pressure, 13,14,34 while other studies report V O -related deep states.…”

Section: Introductionmentioning

confidence: 99%

Influence of annealing atmosphere on formation of electrically-active defects in rutile TiO2

Zimmermann

Bonkerud

Herklotz

et al. 2018

Journal of Applied Physics

View full text Add to dashboard Cite

Electronic states in the upper part of the bandgap of reduced and/or hydrogenated n-type rutile TiO2 single crystals have been studied by means of thermal admittance and deep-level transient spectroscopy measurements. The studies were performed at sample temperatures between 28 and 300 K. The results reveal limited charge carrier freeze-out even at 28 K and evidence the existence of dominant shallow donors with ionization energies below 25 meV. Interstitial atomic hydrogen is considered to be a major contributor to these shallow donors, substantiated by infrared absorption measurements. Three defect energy levels with positions of about 70 meV, 95 meV, and 120 meV below the conduction band edge occur in all the studied samples, irrespective of the sample production batch and the post-growth heat treatment used. The origin of these levels is discussed in terms of electron polarons, intrinsic point defects, and/or common residual impurities, where especially interstitial titanium atoms, oxygen vacancies, and complexes involving Al atoms appear as likely candidates. In contrast, no common deep-level defect, exhibiting a charge state transition in the 200–700 meV range below the conduction band edge, is found in different samples. This may possibly indicate a strong influence on deep-level defects by the post-growth heat treatments employed.

show abstract

“…4,24,28 In the case of the high-T c cuprate superconductors the MIR band softening was interpreted in terms of large polaron models including polaron-polaron interactions.…”

mentioning

confidence: 99%

Signatures of polaronic excitations in quasi-one-dimensionalLaTiO3.41

et al. 2003

View full text Add to dashboard Cite

The optical properties of quasi-one-dimensional metallic LaTiO3.41 are studied for the polarization along the a and b axes. With decreasing temperature modes appear along both directions suggestive for a phase transition. The broadness of these modes along the conducting axis might be due to the coupling of the phonons to low-energy electronic excitations across an energy gap. We observe a pronounced midinfrared band with a temperature dependence consistent with (interacting) polaron models. The polaronic picture is corroborated by the presence of strong electron-phonon coupling and the temperature dependence of the dc conductivity.Titanium oxide compounds have been investigated extensively over the last decades, at the latest since the discovery of high-T c superconductivity in the cuprates, to study the role of electronic correlations and to explore the doping induced transition from a Mott insulator to a metal, like, e.g., in La 1−y Sr y TiO 3 .1,2 Of further interest are the titanates because of the proposed polaronic nature of their charge carriers. For example, the existence of small polarons in La 1−γ TiO 3±δ was shown by dc resistivity and thermoelectric power measurements.2,3 Signatures of polaronic carriers were also found in the optical response of TiO 2 , BaTiO 3 , and SrTiO 3 in the form of a midinfrared (MIR) band.4-8 Since a MIR band of (spin-) polaronic origin at ≈1000 cm −1 was also found in several cuprates 9-12 it seems to be a characteristic feature of this class of compounds for low doping as well. The proposal that (bi)polarons might play a major role for the high-T c superconductivity 13 stimulated a vast amount of experimental investigations on this issue.On the other hand, the nature of the polaronic carriers in the titanates is still under discussion. In this paper we present the optical properties of another titanium oxide compound, LaTiO 3.41 , to search for polaronic signatures and test their compatibility with the existing models. Indeed, we find a strong MIR band in the optical response showing a strong temperature dependence. A particular property of LaTiO 3.41 is its quasione-dimensional (quasi-1D) metallic character which was recently found by resistivity measurements.14 It is interesting to note that a MIR band was also observed for a variety of organic and anorganic quasi-1D metals, like

show abstract

Optical Absorption by Polarons in Rutile (TiO₂) Single Crystals

Cited by 94 publications

References 20 publications

On the Experimental Observation of Small Polarons in Rutile (TiO₂)

On the Experimental Observation of Small Polarons in Rutile (TiO₂)

Influence of annealing atmosphere on formation of electrically-active defects in rutile TiO2

Signatures of polaronic excitations in quasi-one-dimensionalLaTiO3.41

Contact Info

Product

Resources

About

Optical Absorption by Polarons in Rutile (TiO2) Single Crystals

Cited by 94 publications

References 20 publications

On the Experimental Observation of Small Polarons in Rutile (TiO2)

On the Experimental Observation of Small Polarons in Rutile (TiO2)

Influence of annealing atmosphere on formation of electrically-active defects in rutile TiO2

Signatures of polaronic excitations in quasi-one-dimensionalLaTiO3.41

Contact Info

Product

Resources

About

Optical Absorption by Polarons in Rutile (TiO₂) Single Crystals

On the Experimental Observation of Small Polarons in Rutile (TiO₂)

On the Experimental Observation of Small Polarons in Rutile (TiO₂)