Raman Spectroscopy Study of alpha-, beta-, gamma-NaxCoO2 and gamma-(Ca,Sr)xCoO2

H. F. Tian; H. X. Yang; J. Q. Li; R. J. Xiao; X. Liu; Y. G. Shi; Y. L. Liu; Y. Xia

REVIEW

Raman Spectroscopy Study of alpha-, beta-, gamma-NaxCoO2 and gamma-(Ca,Sr)xCoO2

H. X. Yang, Y. Xia, Y. G. Shi, H. F. Tian, R. J. Xiao, X. Liu, Y. L. Liu, J. Q. Li

Superconductivity · Submitted 21 Feb 2006 · 36 references

Pith's verdict: A useful phase-fingerprint Raman dataset for NaxCoO2 and (Ca,Sr)xCoO2, whose central stacking assignments are credible but the cation-ordering zone-folding interpretation is speculative and needs support.

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arXiv IDcond-mat/0602489 (version 2)

Pith IDDSQBUJFC, Pith's permanent record of this paper and its review

CitationH. F. Tian, H. X. Yang, J. Q. Li, R. J. Xiao, X. Liu, Y. G. Shi, Y. L. Liu, Y. Xia. "Raman Spectroscopy Study of alpha-, beta-, gamma-NaxCoO2 and gamma-(Ca,Sr)xCoO2." arXiv:cond-mat/0602489 (2006). https://pith.science/paper/DSQBUJFC

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Editor's note

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Worth a serious look if you work on cobalt-oxide phonons. The genuinely new content is the Raman data on alpha-NaCoO2 and beta-Na0.6CoO2, plus the first spectra of the gamma-(Ca,Sr)xCoO2 series; the five-mode spectrum of gamma-Na0.75CoO2 repeats their own earlier paper. That new data is useful: the paper connects each spectrum to XRD and TEM-confirmed phase identity, which is exactly the missing piece in earlier conflicting Raman reports. Their two-mode alpha and five-mode gamma assignments are consistent with group theory and with the data shown. The warning that deintercalated "single crystals" can contain stacked alpha/beta/gamma intergrowths is well-taken and worth remembering.

Soft spots, in rough order:

- The abstract says four Raman active phonons for beta-Na0.6CoO2, but the body reports three observed peaks and nine predicted modes explained by overlap. That is not a fatal error, but it needs reconciling before publication. - The text lists 673.3 cm-1 twice, once as A1g and once as an E2g, in the gamma assignment. Obvious typo, but symptomatic of rushed editing. - The Sr0.35CoO2 ~148 cm-1 mode is attributed to Brillouin-zone folding from the sqrt3 x sqrt3 superstructure, with no polarization data and no lattice-dynamics calculation; samples are polycrystalline. Sr content, conductivity, and skin depth also change in the same compositional window, so the mode is not cleanly tied to ordering. Ca0.3CoO2 has the same superstructure but no 148 cm-1 mode, and the "less well-defined/coexistence" explanation is post hoc. The ordering-induced spectral changes are plausible and worth reporting, but the zone-folding mechanism is not established. - The alpha/beta/gamma comparison varies Na content along with stacking. They themselves note A1g is sensitive to Na-layer occupancy, so calling it an interlayer-stacking effect is partially confounded. A sentence or two of qualification would be enough.

There are no parameter fits passed off as predictions, no invented entities, and the qualitative conclusions are not load-bearing erroneous. I would send it to review, but with a clear request to fix the beta inconsistency, the typo, and soften the zone-folding claim to a suggestion rather than an assignment.

If my group were in this subfield I would cite it for the alpha/beta reference spectra. For a general reading group it is maybe, not must.

Referee report

Significance

If the assignments are correct, the paper provides a useful framework for reconciling conflicting Raman data on sodium cobaltates: the alpha, beta, and gamma polytypes have different numbers of zone-center Raman phonons, and samples described as gamma may contain alpha-phase surfaces or intergrowths. The paper's strength is its combination of XRD, TEM, and Raman on structurally characterized phases, and its group-theory counting is standard and internally coherent for the alpha and gamma phases. The cautionary TEM evidence for phase coexistence in Na0.5CoO2 is a valuable methodological contribution. However, the paper's most novel quantitative claim - that cation ordering produces specific new Raman features such as the 148 cm-1 mode - is not backed by a lattice-dynamics calculation, polarization-resolved data, or a fixed-composition control. The beta-phase discussion is also incomplete because the predicted nine modes are not reconciled with the three observed peaks. The qualitative stacking dependence is likely correct, but the cation-ordering mechanism is currently only a hypothesis.

Major objections (3)

[Abstract and Section 3, Fig. 2] The abstract states that there are four Raman active phonons for beta-NaCoO2, but the text reports only three strong peaks (around 461, 577, and 691 cm-1) and does not identify a fourth mode. The factor-group analysis predicts nine modes (5Ag+4Bg), and the statement that the discrepancy is due to peak overlap is made without any fitting, polarization data, or single-crystal measurements. The beta phase therefore does not currently provide a clean test of the stacking-count argument, and the abstract's 'four phonons' is unsupported. The abstract should be corrected to match the observed three peaks, or the fourth mode should be explicitly assigned and justified.
[Section 3, Figs. 4(a) and 4(b)] The attribution of the ~148 cm-1 mode in Sr0.35CoO2 to Brillouin-zone folding from the sqrt(3) x sqrt(3) superstructure is not established. The comparison is made across different Sr contents (x = 0.15, 0.25, 0.35, 0.40), so the Sr concentration, carrier concentration, and optical skin depth all change simultaneously; the paper itself notes a metal-insulator crossover near x ~ 0.35. No zone-folding or factor-group calculation for the sqrt(3) x sqrt(3) supercell is provided, and the polycrystalline backscattering geometry gives no polarization information about the symmetry of the 148 cm-1 mode. The authors' own data on Ca0.3CoO2, which also has a sqrt(3) x sqrt(3) superstructure, show no 148 cm-1 mode, and the explanation of 'coexistence of complex multiple superstructures' is post hoc. The conclusion that cation ordering 'could result in visible alterations' is therefore suggestive but needs either a fixed-composition ordering control, a zone-folding calculation, or explicit downgrading of this part of the claim to a speculation.
[Section 3, Fig. 2] The central comparison of the alpha, beta, and gamma phases is confounded with Na content, because alpha-NaCoO2, beta-Na0.6CoO2, and gamma-Na0.75CoO2 have different stoichiometries. The text itself notes that the A1g energy strongly depends on the occupancy of the Na layer. Thus, while the number of Raman-active modes is determined by the stacking symmetry, the reported frequency differences among the three phases cannot be attributed uniquely to the CoO6 stacking sequence. A statement acknowledging this limitation is needed in the conclusions, or the paper should compare samples with matched Na content where the stacking differs.

Minor objections (4)

[Section 3, gamma-Na0.75CoO2 mode list] The sentence listing gamma-Na0.75CoO2 modes contains six numbers: A1g at 673.3 cm-1, E1g at 188.5 cm-1, and E2g at 470.4, 510.7, 605.8, and 673.3 cm-1. Since five modes are claimed, the second 673.3 appears to be a typographical error and should be removed or corrected.
[Throughout and Fig. 5 caption] There are several typographical errors: 'Brillouine' should be 'Brillouin' (twice), 'new mood' should be 'new mode', 'theses peaks' should be 'these peaks', and the Fig. 5 caption 'taken alone [010] zone-axis' should be 'taken along [010]'.
[Section 3, Fig. 4 caption] The Fig. 4(b) caption states that the spectra show 'spectral features arising from cation ordering,' but for several compositions the ordering state is not directly characterized in this paper; the text itself invokes phase separation and multiple superstructures. The caption should be phrased more cautiously, e.g., 'spectral changes accompanying changes in Ca content and ordering.'
[Section 3 and Ref. [31]] The metal-insulator crossover near x ~ 0.35 in SrxCoO2 is supported only by an unpublished reference [31]. Since this crossover is used to explain the changing signal-to-noise ratio, the associated data should be included or a published source cited.

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The paper

The paper claims

The number and energy of Raman-active phonons in NaxCoO2 track the CoO6 stacking sequence and the ordering of intercalated Ca/Sr cations.

The reading

Raman spectra of three Na$_x$CoO$_2$ polytypes that differ in the stacking of their CoO$_6$ octahedra along the $c$ axis are compared: $\alpha$-NaCoO$_2$, $\beta$-Na$_{0.6}$CoO$_2$, and $\gamma$-Na$_{0.75}$CoO$_2$. The number and energy of the observable phonons follow the stacking sequence, with two modes in $\alpha$, three strong peaks in $\beta$, and five modes in $\gamma$. In the $\gamma$ phases with Ca or Sr between the CoO$_2$ layers, the Raman spectra change visibly when the intercalated cations order into a $\sqrt{3}\times\sqrt{3}$ superstructure; Sr$_{0.35}$CoO$_2$ even shows a new mode near 148 cm$^{-1}$ that the authors attribute to Brillouin-zone folding. The paper concludes that interlayer interaction and local structural features, not just the isolated CoO$_2$ sheets, control the lattice dynamics of this layered family.

What carries the argument

The carrying object is the factor-group analysis of Raman-active phonon modes for each polytype: $A_{1g}+E_g$ for $\alpha$, $5A_g+4B_g$ for $\beta$, and $A_{1g}+E_{1g}+3E_{2g}$ for $\gamma$, where the labels name the symmetry species of the vibrational modes. This machinery assigns each observed peak to a mode type and accounts for which atoms move (oxygen only for the $A_{1g}$ and $E_{1g}$ modes of $\gamma$; sodium and oxygen for some $E_{2g}$ modes). The second carrying ingredient is the electron-diffraction and high-resolution TEM identification of the $\sqrt{3}\times\sqrt{3}$ cation superstructure in ordered Sr$_{0.35}$CoO$_2$, which the paper uses to explain the extra 148 cm$^{-1}$ peak as a Brillouin-zone-folding effect.

Extended reading notes

Core claim

On the paper's own terms, the central discovery is that the Raman-active phonon spectrum of Na$_x$CoO$_2$ is a structural fingerprint of the CoO$_6$ stacking sequence. $\alpha$-NaCoO$_2$ (space group $R\bar{3}m$) shows two oxygen-derived modes at 486.5 and 586.4 cm$^{-1}$; $\beta$-Na$_{0.6}$CoO$_2$ ($C2/m$) shows three strong peaks near 461, 577, and 691 cm$^{-1}$, fewer than the nine symmetry-allowed modes because of overlap; and $\gamma$-Na$_{0.75}$CoO$_2$ ($P6_3/mmc$) shows five modes at 188.5, 470.4, 510.7, 605.8, and 673.3 cm$^{-1}$. The paper further claims that cation ordering alters the spectra: $\gamma$-(Ca,Sr)$_x$CoO$_2$ with $x = 0.15$ and $0.25$ keeps the five $\gamma$ phonons shifted to higher frequency, while Sr$_{0.35}$CoO$_2$, with a well-defined $\sqrt{3}\times\sqrt{3}$ superstructure, acquires a new mode near 148 cm$^{-1}$ assigned to zone folding. These observations lead to the conclusion that interlayer interaction and local structural features govern the lattice dynamics and physical properties of this layered system.

Load-bearing premise

The comparisons assume that the observed spectral differences are caused by the CoO$_6$ stacking sequence and by cation ordering, even though the sodium content also differs between the three phases, the out-of-plane oxygen vibration is known to depend on how full the sodium layer is, and the 148 cm$^{-1}$ zone-folding assignment lacks a lattice-dynamics calculation or polarization data.

Editorial extensions

If this is right

Raman scattering becomes a quick structural fingerprint for telling $\alpha$-, $\beta$-, and $\gamma$-Na$_x$CoO$_2$ apart, even in polycrystalline samples.
Conflicting Raman results in the literature can be reconciled by sample phase: nominally similar Na$_x$CoO$_2$ crystals can be $\alpha$-, $\beta$-, or $\gamma$-stacked, and the TEM images here show $\gamma$/$\beta$ intergrowth in deintercalated Na$_{0.5}$CoO$_2$.
The shift of the oxygen-derived $A_{1g}$ and $E_{1g}$ modes to higher frequency in $\gamma$-(Ca,Sr)$_x$CoO$_2$ indicates stronger electrostatic coupling between divalent cations and the CoO$_2$ layers, a factor relevant to thermoelectric and superconducting behavior.
Any lattice-dynamics model of these layered cobalt oxides must include interlayer interactions to reproduce the observed stacking- and ordering-sensitive phonon structure.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

A decisive test would measure Raman spectra of $\alpha$-, $\beta$-, and $\gamma$-phases at fixed sodium content (or vary sodium content within one stacking type); if the stacking-specific mode pattern survives, the stacking claim is cleanly confirmed.
The zone-folding interpretation of the 148 cm$^{-1}$ mode predicts that the $\sqrt{3}\times\sqrt{3}$ superstructure should also fold other phonons at different wavevectors, so inelastic neutron or x-ray scattering on Sr$_{0.35}$CoO$_2$ could look for the corresponding zone-boundary modes.
Since Raman scattering is contact-free, it could be a practical probe of cation ordering and stacking in air-sensitive or electron-beam-sensitive layered oxides such as Li$_x$CoO$_2$, where TEM observations risk altering the cation arrangement.
The linewidth and lineshape changes in the Ca series could be quantified and correlated with ordering coherence lengths from TEM, turning the qualitative "visible alterations" into a quantitative measure of how ordering length controls phonon damping.

Original abstract

Raman spectroscopy measurements have been performed on alpha-, beta-, gamma-NaxCoO2 phases differing in their stacking of CoO6 octahedra along the c-axis direction. The results demonstrate that, in general, there are five active phonons for gamma-Na0.75CoO2, two Raman active phonons for alpha-NaCoO2, and four Raman active phonons for beta-NaCoO2. We have also performed Raman scattering measurements on several gamma-(Ca,Sr)xCoO2 (0.15 <= x <= 0.35) samples which show well-defined intercalated Ca/Sr-ordering. The experimental data show that the intercalated cation ordering could result in visible alterations on Raman spectral structures. The observations of the spectral changes along with the variation of the CoO6 stacking, as well as the intercalated Sr/Ca ordering suggest that the interlayer interaction plays an important role for understanding the lattice dynamics in this layered system.

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Compiled by classifier-1.13-20260917 via OpenRouter, question bank abstract-p1-20260923, 2026-09-23: 1 request, 4,467 input tokens, $0.0002 reported.

What the abstract itself states, as probabilities: claims first 0.02 · states limitation 0.06 · human participants 0.02 · controlled comparison 0.07 · randomized assignment 0.01 · states quantitative result 0.98 · compares with prior results 0.10 · mentions code or data availability 0.01.

The abstract, sentence by sentence

arXiv listing abstract v2. Results and the main claim are underlined; show every role.

Raman spectroscopy measurements have been performed on alpha-, beta-, gamma-NaxCoO2 phases differing in their stacking of CoO6 octahedra along the c-axis direction. The results demonstrate that, in general, there are five active phonons for gamma-Na0.75CoO2, two Raman active phonons for alpha-NaCoO2, and four Raman active phonons for beta-NaCoO2. We have also performed Raman scattering measurements on several gamma-(Ca,Sr)xCoO2 (0.15 <= x <= 0.35) samples which show well-defined intercalated Ca/Sr-ordering. The experimental data show that the intercalated cation ordering could result in visible alterations on Raman spectral structures. The observations of the spectral changes along with the variation of the CoO6 stacking, as well as the intercalated Sr/Ca ordering suggest that the interlayer interaction plays an important role for understanding the lattice dynamics in this layered system.

background contribution method result interpretation main claim

What the classifier reports for each sentence. The number is the probability it gave the label.
#	sentence	role	the authors' own work	states the main conclusion	strength
s0	Raman spectroscopy measurements have been performed on alpha-, beta-, gamma-NaxCoO2 phases differing in their stacking of CoO6 octahedra along the c-axis direction.	contribution 0.57	0.94	0.03	asserted 1.00
s1	The results demonstrate that, in general, there are five active phonons for gamma-Na0.75CoO2, two Raman active phonons for alpha-NaCoO2, and four Raman active phonons for beta-NaCoO2.	result 1.00	0.94	0.09	asserted 1.00
s2	We have also performed Raman scattering measurements on several gamma-(Ca,Sr)xCoO2 (0.15 <= x <= 0.35) samples which show well-defined intercalated Ca/Sr-ordering.	contribution 0.79	0.97	0.04	asserted 1.00
s3	The experimental data show that the intercalated cation ordering could result in visible alterations on Raman spectral structures.	result 0.90	0.93	0.13	hedged possibility 0.90
s4	The observations of the spectral changes along with the variation of the CoO6 stacking, as well as the intercalated Sr/Ca ordering suggest that the interlayer interaction plays an important role for understanding the lattice dynamics in this layered system.	interpretation 1.00	0.85	0.83	hedged possibility 0.99

What kind of paper the classifier reports this is: empirical study 1.00 · evidence from observation or experiment 1.00.

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sources read

arXiv listing abstract v2

not examined

full text
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relations to other papers

levels run

P abstract

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S sections
T body sentences
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R cross-paper relations

Every quoted sentence on this record is the authors'. Every label is from Pith's closed vocabulary, with the probability shown beside it. Every number in the measurements table is the authors', checked by code. Record as JSON

References

Works cited (36)

[1]

Introduction Layered NaxCoO2 materials have been extensively investigated in recent years due to a notably large thermoelectric power coexis ting with superconductivity and complex charge-ordering (CO) transitions [1-3]. In or der to understand the lattice dynamics in this layered system, Raman scattering [4-9], infr ared absorption [10], and neutron scat...

View on Pith
[2]

Experimental Polycrystalline samples of α-NaCoO2, β-Na0.6CoO2, γ-Na0.75CoO2 and (Sr,Ca)xCoO2 (0.15 ≤ x ≤ 0.40) materials were used in our Raman scattering study. The γ-Na0.75CoO2 phase was synthesized following the proce dure as described in Ref [17], while α-NaCoO2 and β-Na0.6CoO2 were prepared by conventional solid-state reactions at relatively lower te...

View on Pith
[3]

Results and discussion Figure 1(a) shows the XRD patterns for the α-NaCoO2, β-Na0.6CoO2 and γ-Na0.75CoO2 phases. These phases differ crystallogra phically in the stacking patterns of CoO6 octahedra along the c-axis direction [15-21]. In the α-NaxCoO2 system, the parent phase with a nominal composition of α-NaCoO2 has a hexagonal ce ll with lattice paramet...

View on Pith
[4]

zone-axis HRTEM image for Sr 0.35CoO2, illustrating the atomic structure for this superstructure. The image was obtained from a th in region of the crystal near the Scherzer defocus value ( ≈-60nm). The metal atom (Co) positions are therefore recognizable as dark dots. In this image, the hexagona l superstructure is clearly seen in the relative thick area...

View on Pith
[5]

Conclusions The Raman scattering spectra obtained from the α, β, γ -NaxCoO2 phases, γ-CaxCoO2 and γ-SrxCoO2 (0.15 ≤ x ≤ 0.40) materials have been an alyzed. Experimental results demonstrate that the Raman spectra from α, β, and γ -Na xCoO2 phases have notably different structural features. In genera l, five Raman active phonons at around 186 cm -1 (E1g), ...

View on Pith
[6]

I. Terasaki, Y . Sasago, K. Uchinokura, Phys. Rev. B, 56, R12685 (1997)

View on Pith 1997
[7]

K. Takada, H. Sakurai, E. Takayama-Murom achi, F. Izumi, R.A. Dilanian and T. Sasaki, Nature, 422, 53 (2003)

View on Pith 2003
[8]

M.L. Foo, Y .Y . Wang, S. Watauchi, H.W. Zandbergen, T. He, R.J. Cava, and N.P. Ong, Phys. Rev. Lett. 92, 247001 (2004)

View on Pith 2004
[9]

Y.G. Shi, Y.L. Liu, H.X. Yang, C.J. Nie, R. Jin, J.Q. Li, Phys. Rev. B , 70, 052502 (2004)

View on Pith 2004
[10]

P. Lemmens, V. Gnezdilov, N.N. Kovaleva, et al ., J. Phy. : -Cond. Matt., 16, S857-S865 (2004)

View on Pith 2004
[11]

H.X. Yang, C.J. Nie, Y.G. Shi, H.C. Yu, S. Ding, Y.L. Liu, D. Wu, N.L. Wang, J.Q. Li, Solid State Commun.134, 403 (2005)

View on Pith 2005
[12]

X.N. Zhang, P. Lemmens, , V. Gnezdilov, K. Y. Choi, B. Keimer, D.P. Chen, C.T. Lin, F.C. Chou, Physica B 359-361, 424 (2005)

View on Pith 2005
[13]

M.N. Iliev, A.P. Litvinchuk, R.L. Meng, Y.Y. Sun, J. Cmaidalka, C.W. Chu. Physica C, 402, 239 (2004)

View on Pith 2004
[14]

P. Lemmens, K.Y. Choi, V. Gnezdilov, E. Ya.Sherman, D.P. Chen, C.T. Lin, F.C. Chou, B. Keimer, Phys. Rev. Lett., 96, 167204 (2006)

View on Pith 2006
[15]

N.L. Wang, D. Wu, G . Li, X. H. Chen, C.H. Wang, X.G . Lou, Phys. Rev. Lett . 93, 147403 (2004)

View on Pith 2004
[16]

J.W. Lynn, Q. Huang, C.M. Brown, V.L. Mille r, M.L. Foo, R.E. Schaak, C. Y. Jones, E.A. Mackey, and R.J. Cava, Phys. Rev. B 68, 214516 (2003). 16

View on Pith 2003
[17]

Z.Y. Li, J.L. Yang, J.G. Hou and Q.S. Zhu, Phys. Rev. B 70, 144518 (2004)

View on Pith 2004
[18]

J.F. Qu, W. Wang, Y. Chen, G. Li, X.G. Li, Phys. Rev. B, 73, 092518 (2006)

View on Pith 2006
[19]

Y.G. Shi, H.X. Yang, H. Huang, X. Liu, and J.Q. Li*, Phys. Rev. B, 73, 094505 (2006)

View on Pith 2006
[20]

K. Takada, H. Sakurai, E. Takayama-Murom achi, F. Izumi, R.A. Dilanian, and T. Sasaki, Adv. Mater. 16, 1901 (2004)

View on Pith 2004
[21]

S. Mistry, D.C. Arnold, C. J. Nuttall, A. Lappas and M. A. Green, Chem. Commun., 2440 (2004)

View on Pith 2004
[22]

C. Fouassier, Gn. Matejka, J.-M. Reau, and P.J. Hagenmuller, J. Solid State Chem . 6, 532 (1973)

View on Pith 1973
[23]

T. Motohashi, R. Ueda, E. Naujalis, T. Toj o, I. Terasaki, T. Atake, M. Karppinen, H. Yamauchi, Physical Review B 67,064406(2003)

View on Pith 2003
[24]

M.L. Foo, T. Klimczuk, L Li, N.P. Ong, R.J. Cava. Solid State Commun. 133, 407 (2005)

View on Pith 2005
[25]

Y. Takahash, Y. Gotoh, J. Akimoto, J. Solid State Chem. 172, 22 (2003)

View on Pith 2003
[26]

Y . Ono, R. Ishikawa, Y . Miyazaki, Y . Ishii, Y . Morii, and T. Kajitani, J. Solid State Chem., 166, 177 (2002)

View on Pith 2002
[27]

P.H. Zhang, R.B. Capaz, M.L. Cohen, S.G . Louie, Phys. Rev. B, 71, 153102 (2005)

View on Pith 2005
[28]

A. Van der Ven, M. K. Aydinol, G . Ceder, G . Kresse and J. Hafner, Phys. Rev. B 58, 2975 (2004)

View on Pith 2004
[29]

H.X. Yang, Y .G . Shi, X. Liu, R.J. Xiao, H.F. Tian and J.Q. Li, , Phys. Rev. B 73, 014109 (2006)

View on Pith 2006
[30]

H.X. Yang, Y .G . Shi, Y .Q. Guo, X. Liu, R.J. Xiao, J.L. Luo, J.Q. Li, 17 cond-mat/0503136

View on Pith Pith review arXiv
[31]

E. Kroumova, M.I. Aroyo, J.M. Perez-Mato, A. Kirov, C. Capillas, S. Ivantchev, H. Wondratschek, Phase Transitions 76, 155 (2003)

View on Pith 2003
[32]

M.L. Foo, Y . Wang, S.Watauchi, H.W. Zandbergen, T. He, R.J. Cava, and N.P. Ong, Phys. Rev. Lett. 92, 247001 (2004)

View on Pith 2004
[33]

B.L. Cushing, J.B. Wiley, J. Solid. State. Chem. 141, 385 (1998)

View on Pith 1998
[34]

I. Levin, S.A. Prosandeev, and J.E. Maslar, Applied Physics Letters 86, 011919 (2005)

View on Pith 2005
[35]

H.W. Zandbergen, M. Foo, Q. Xu, V . Kumar, R.J. Cava, Phys. Rev. B , 70, 024101 (2004)

View on Pith 2004
[36]

Y.Q. Guo, J.L. Luo, G.T. Liu, H.X. Yang, J.Q. Li, N.L. Wang, D. Jin, unpublished. 18 Figure Captions Fig. 1: (a) XRD patterns for parent phases of α-NaCoO2, β-Na0.6CoO2 and γ-Na0.75CoO2. The lattice parameters for all phases are shown for comparison. (b) Structural models of α-NaCoO2, β-Na0.6CoO2 and γ-Na0.75CoO2 phases. Fig. 2 : Raman spectra of the α-Na...

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Discussion

Disagree with the review, or know something it missed? Leave a comment, highlight any passage above to comment on it, or challenge this review formally.

[1] [1]

Introduction Layered NaxCoO2 materials have been extensively investigated in recent years due to a notably large thermoelectric power coexis ting with superconductivity and complex charge-ordering (CO) transitions [1-3]. In or der to understand the lattice dynamics in this layered system, Raman scattering [4-9], infr ared absorption [10], and neutron scat...

View on Pith

[2] [2]

Experimental Polycrystalline samples of α-NaCoO2, β-Na0.6CoO2, γ-Na0.75CoO2 and (Sr,Ca)xCoO2 (0.15 ≤ x ≤ 0.40) materials were used in our Raman scattering study. The γ-Na0.75CoO2 phase was synthesized following the proce dure as described in Ref [17], while α-NaCoO2 and β-Na0.6CoO2 were prepared by conventional solid-state reactions at relatively lower te...

View on Pith

[3] [3]

Results and discussion Figure 1(a) shows the XRD patterns for the α-NaCoO2, β-Na0.6CoO2 and γ-Na0.75CoO2 phases. These phases differ crystallogra phically in the stacking patterns of CoO6 octahedra along the c-axis direction [15-21]. In the α-NaxCoO2 system, the parent phase with a nominal composition of α-NaCoO2 has a hexagonal ce ll with lattice paramet...

View on Pith

[4] [4]

zone-axis HRTEM image for Sr 0.35CoO2, illustrating the atomic structure for this superstructure. The image was obtained from a th in region of the crystal near the Scherzer defocus value ( ≈-60nm). The metal atom (Co) positions are therefore recognizable as dark dots. In this image, the hexagona l superstructure is clearly seen in the relative thick area...

View on Pith

[5] [5]

Conclusions The Raman scattering spectra obtained from the α, β, γ -NaxCoO2 phases, γ-CaxCoO2 and γ-SrxCoO2 (0.15 ≤ x ≤ 0.40) materials have been an alyzed. Experimental results demonstrate that the Raman spectra from α, β, and γ -Na xCoO2 phases have notably different structural features. In genera l, five Raman active phonons at around 186 cm -1 (E1g), ...

View on Pith

[6] [6]

I. Terasaki, Y . Sasago, K. Uchinokura, Phys. Rev. B, 56, R12685 (1997)

View on Pith 1997

[7] [7]

K. Takada, H. Sakurai, E. Takayama-Murom achi, F. Izumi, R.A. Dilanian and T. Sasaki, Nature, 422, 53 (2003)

View on Pith 2003

[8] [8]

M.L. Foo, Y .Y . Wang, S. Watauchi, H.W. Zandbergen, T. He, R.J. Cava, and N.P. Ong, Phys. Rev. Lett. 92, 247001 (2004)

View on Pith 2004

[9] [9]

Y.G. Shi, Y.L. Liu, H.X. Yang, C.J. Nie, R. Jin, J.Q. Li, Phys. Rev. B , 70, 052502 (2004)

View on Pith 2004

[10] [10]

P. Lemmens, V. Gnezdilov, N.N. Kovaleva, et al ., J. Phy. : -Cond. Matt., 16, S857-S865 (2004)

View on Pith 2004

[11] [11]

H.X. Yang, C.J. Nie, Y.G. Shi, H.C. Yu, S. Ding, Y.L. Liu, D. Wu, N.L. Wang, J.Q. Li, Solid State Commun.134, 403 (2005)

View on Pith 2005

[12] [12]

X.N. Zhang, P. Lemmens, , V. Gnezdilov, K. Y. Choi, B. Keimer, D.P. Chen, C.T. Lin, F.C. Chou, Physica B 359-361, 424 (2005)

View on Pith 2005

[13] [13]

M.N. Iliev, A.P. Litvinchuk, R.L. Meng, Y.Y. Sun, J. Cmaidalka, C.W. Chu. Physica C, 402, 239 (2004)

View on Pith 2004

[14] [14]

P. Lemmens, K.Y. Choi, V. Gnezdilov, E. Ya.Sherman, D.P. Chen, C.T. Lin, F.C. Chou, B. Keimer, Phys. Rev. Lett., 96, 167204 (2006)

View on Pith 2006

[15] [15]

N.L. Wang, D. Wu, G . Li, X. H. Chen, C.H. Wang, X.G . Lou, Phys. Rev. Lett . 93, 147403 (2004)

View on Pith 2004

[16] [16]

J.W. Lynn, Q. Huang, C.M. Brown, V.L. Mille r, M.L. Foo, R.E. Schaak, C. Y. Jones, E.A. Mackey, and R.J. Cava, Phys. Rev. B 68, 214516 (2003). 16

View on Pith 2003

[17] [17]

Z.Y. Li, J.L. Yang, J.G. Hou and Q.S. Zhu, Phys. Rev. B 70, 144518 (2004)

View on Pith 2004

[18] [18]

J.F. Qu, W. Wang, Y. Chen, G. Li, X.G. Li, Phys. Rev. B, 73, 092518 (2006)

View on Pith 2006

[19] [19]

Y.G. Shi, H.X. Yang, H. Huang, X. Liu, and J.Q. Li*, Phys. Rev. B, 73, 094505 (2006)

View on Pith 2006

[20] [20]

K. Takada, H. Sakurai, E. Takayama-Murom achi, F. Izumi, R.A. Dilanian, and T. Sasaki, Adv. Mater. 16, 1901 (2004)

View on Pith 2004

[21] [21]

S. Mistry, D.C. Arnold, C. J. Nuttall, A. Lappas and M. A. Green, Chem. Commun., 2440 (2004)

View on Pith 2004

[22] [22]

C. Fouassier, Gn. Matejka, J.-M. Reau, and P.J. Hagenmuller, J. Solid State Chem . 6, 532 (1973)

View on Pith 1973

[23] [23]

T. Motohashi, R. Ueda, E. Naujalis, T. Toj o, I. Terasaki, T. Atake, M. Karppinen, H. Yamauchi, Physical Review B 67,064406(2003)

View on Pith 2003

[24] [24]

M.L. Foo, T. Klimczuk, L Li, N.P. Ong, R.J. Cava. Solid State Commun. 133, 407 (2005)

View on Pith 2005

[25] [25]

Y. Takahash, Y. Gotoh, J. Akimoto, J. Solid State Chem. 172, 22 (2003)

View on Pith 2003

[26] [26]

Y . Ono, R. Ishikawa, Y . Miyazaki, Y . Ishii, Y . Morii, and T. Kajitani, J. Solid State Chem., 166, 177 (2002)

View on Pith 2002

[27] [27]

P.H. Zhang, R.B. Capaz, M.L. Cohen, S.G . Louie, Phys. Rev. B, 71, 153102 (2005)

View on Pith 2005

[28] [28]

A. Van der Ven, M. K. Aydinol, G . Ceder, G . Kresse and J. Hafner, Phys. Rev. B 58, 2975 (2004)

View on Pith 2004

[29] [29]

H.X. Yang, Y .G . Shi, X. Liu, R.J. Xiao, H.F. Tian and J.Q. Li, , Phys. Rev. B 73, 014109 (2006)

View on Pith 2006

[30] [30]

H.X. Yang, Y .G . Shi, Y .Q. Guo, X. Liu, R.J. Xiao, J.L. Luo, J.Q. Li, 17 cond-mat/0503136

View on Pith Pith review arXiv

[31] [31]

E. Kroumova, M.I. Aroyo, J.M. Perez-Mato, A. Kirov, C. Capillas, S. Ivantchev, H. Wondratschek, Phase Transitions 76, 155 (2003)

View on Pith 2003

[32] [32]

M.L. Foo, Y . Wang, S.Watauchi, H.W. Zandbergen, T. He, R.J. Cava, and N.P. Ong, Phys. Rev. Lett. 92, 247001 (2004)

View on Pith 2004

[33] [33]

B.L. Cushing, J.B. Wiley, J. Solid. State. Chem. 141, 385 (1998)

View on Pith 1998

[34] [34]

I. Levin, S.A. Prosandeev, and J.E. Maslar, Applied Physics Letters 86, 011919 (2005)

View on Pith 2005

[35] [35]

H.W. Zandbergen, M. Foo, Q. Xu, V . Kumar, R.J. Cava, Phys. Rev. B , 70, 024101 (2004)

View on Pith 2004

[36] [36]

Y.Q. Guo, J.L. Luo, G.T. Liu, H.X. Yang, J.Q. Li, N.L. Wang, D. Jin, unpublished. 18 Figure Captions Fig. 1: (a) XRD patterns for parent phases of α-NaCoO2, β-Na0.6CoO2 and γ-Na0.75CoO2. The lattice parameters for all phases are shown for comparison. (b) Structural models of α-NaCoO2, β-Na0.6CoO2 and γ-Na0.75CoO2 phases. Fig. 2 : Raman spectra of the α-Na...

View on Pith