{"id":"315e815a-a41b-4afc-ab96-3436094c4682","arxiv_id":"2508.21621","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"The ac conductivity spectra of Ba2SmTaO6 and Sr2SmTaO6 obey time-temperature superposition, while Ca2SmTaO6 does not, a deviation attributed to inhomogeneous grain-boundary disorder.","lead":"This paper measures how electrical conductivity changes with frequency in three double perovskite ceramics and tests whether the curves collapse onto one master curve, a sign of universal transport. It finds that two materials collapse as expected but a third does not, and interprets the failure as evidence of disorder-induced 'glassy' charge dynamics.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"BST/SST collapse is an algebraic consequence of Eq. (2), not independent TTSP evidence; n(T) is unreported and CST's failure is attributed to a two-process spectrum.","rationale":"The paper reports new broadband impedance data on three double perovskites, and the raw spectra genuinely appear to differ across the series. My concern is not about data quality or fabrication but about what the scaling operation proves. Substituting the fitted σ_dc and ω_H from Eq. (2) into the normalized coordinates turns the collapse test into a check of internal consistency of the fit, not a test of TTSP. For CST the paper itself identifies the high-frequency region as containing two contributions—grain-boundary relaxation and grain transport—so a one-term power-law normalization is inadequate; the resulting non-collapse is a modeling consequence. The spin-glass/'dipolar frustration' language is analogical and not independently evidenced: no magnetic measurements, no direct extraction of relaxation-time distributions, and no correlation of the power-law exponent with structural distortion is provided. The most defensible conclusion would be that CST's spectra require a two-process description, not that TTSP is violated by frustration. A concrete re-analysis with independent scaling parameters would settle whether the master curves survive. This reinforces, rather than changes, the reader's CONDITIONAL verdict.","tokens_in":9785,"tokens_out":6815,"duration_ms":88303,"concrete_test":"Extract raw conductance/impedance data and regenerate the scaled spectra with independently determined normalizers: σ_dc from the low-frequency plateau (not the Eq. (2) fit parameter) and ω_s from the peak of Z'' (ω_m), while tabulating n(T) from the high-frequency slope. If BST/SST no longer collapse, or CST collapses, under this non-parametric scaling, the reported master curves are fit-induced. A synthetic control that simulates Eq. (2) with a temperature-independent n should reproduce the BST/SST collapse trivially, demonstrating that the original scaling has no independent physical content.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The scaling protocol built on Eq. (2) cannot by itself provide the TTSP evidence. Equation (2) reads σ_ac = σ_dc[1 + (ω/ω_H)^n]. Dividing by σ_dc and scaling frequency by ω_H gives σ_ac/σ_dc = 1 + (ω/ω_H)^n. Hence the 'collapse' for BST/SST in Figs. 4(c–d) and 5(c–d) is an algebraic identity whenever the fit is good and n is temperature-independent. The paper never reports n(T) or fit residuals, so the reader cannot distinguish a physical master curve from a mathematical consequence of the assumed Jonscher form. Moreover, σ_dc and ω_H are extracted from the same fit, so the σ_dc ∝ ω_H correlation in Figs. 4(b)–6(b) is also not an independent check. Conversely, for CST the text explicitly states that the high-frequency region contains both grain-boundary relaxation and grain transport; a single-power-law normalization cannot collapse a two-process spectrum, so the non-collapse is expected even without any 'dipolar frustration.' The Conclusion's causal claim—that the degree of collapse measures microscopic energetic inhomogeneity—therefore rests on an unverified and, for CST, internally acknowledged superposition artifact. This is the load-bearing weakness: the central empirical signature is not independent of the fitting model.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports ac conductivity and impedance measurements on polycrystalline double perovskites A2SmTaO6 (A = Ba, Sr, Ca) between 303 and 673 K. The authors fit the conductivity spectra to the Jonscher power-law form σ_ac = σ_dc[1 + (ω/ω_H)^n] (Eq. (2)), extract σ_dc and ω_H at each temperature, and show that σ_dc and ω_H are linearly correlated. They then normalize the spectra by σ_dc and scale the frequency axis by either σ_dcT or ω_H, reporting that BST and SST collapse onto a single master curve while CST does not in the high-frequency grain-boundary region. This difference is interpreted as evidence of time–temperature superposition holding mainly in the grain-boundary regime, with deviations attributed to local energetic inhomogeneities and, ultimately, to 'dipolar frustration' and glassy charge dynamics.","tokens_in":10179,"tokens_out":3872,"duration_ms":46750,"significance":"If the scaling analysis were genuinely independent of the assumed fitting form, the comparison across Ba, Sr, and Ca substitution would be a useful contribution to understanding how A-site size and octahedral tilting affect charge transport in double perovskites. The experimental dataset and the attempt to link microstructural disorder to scaling behavior are valuable. The manuscript also correctly draws attention to the need to separate grain and grain-boundary contributions. However, as detailed below, the central empirical signature of TTSP is, by the paper's own Eq. (2), an algebraic consequence of the fitting model when the exponent n is temperature-independent. The paper never reports n(T), fit residuals, or goodness-of-fit statistics, and the correlation between σ_dc and ω_H is between two parameters of the same fit. These gaps undermine the central claim in its current form, although they are potentially addressable in a revision.","major_comments":[{"comment":"The scaling collapse using ω_H is mathematically implied by Eq. (2). Dividing by σ_dc and scaling frequency by ω_H gives σ_ac/σ_dc = 1 + (ω/ω_H)^n, which is automatically a temperature-independent master curve whenever the fit is good and n is constant. The paper never reports n(T), fit residuals, or confidence intervals, so the BST/SST 'collapse' cannot be distinguished from a restatement of the assumed Jonscher form. Please provide n(T), residuals, and a demonstration that the collapse is nontrivial, e.g., by comparing freely fitted n versus fixed-n fits or by showing that the data cannot be collapsed under an alternative scaling hypothesis.","section":"§III, Eq. (2) and Figs. 4(c–d), 5(c–d)"},{"comment":"The σ_dc versus ω_H correlation is between two parameters extracted from the same fit of Eq. (2). The text states that a slope of almost unity 'proves our hypothesis that the relaxation and conduction mechanisms are strongly correlated,' but this is not an independent test. In addition, the text writes σ_dc ∼ ω_H^n where 'n' is the slope, which conflates the power-law exponent of Eq. (2) with the slope of the log-log correlation. Please clarify the distinction and provide independent estimates of ω_H (e.g., from modulus peak frequencies) with uncertainty bounds.","section":"§III, Figs. 4(b), 5(b), 6(b)"},{"comment":"For CST the manuscript explicitly states that the high-frequency region above ω_H contains contributions from both grain-boundary relaxation and long-range grain transport. A single-power-law normalization cannot collapse a two-process spectrum, so the non-collapse of CST is expected even without invoking 'dipolar frustration.' To support the proposed interpretation, the two contributions must be modeled explicitly or the scaling restricted to the frequency window where only one process dominates. Without this, the causal link between non-collapse and microscopic energetic inhomogeneity is unsupported.","section":"§III, Figs. 6(c–d) and following paragraph"},{"comment":"The activation energies are inconsistently reported: the text states 0.12 eV, 0.19 eV, and 0.24 eV for BST, SST, and CST, respectively, but the Fig. 7 captions give 1.2 eV for BST and 0.28 eV for CST. The text also mentions 'non-linear behavior in the Arrhenius plots,' but Fig. 7 shows linear fits. These discrepancies must be reconciled, as the activation energies are used to argue for different energy landscapes and polaronic hopping.","section":"§III, Fig. 7 and text"}],"minor_comments":[{"comment":"The abstract lists A = Ba, Ca, but the paper studies A = Ba, Sr, Ca. Sr is missing. Please correct.","section":"Abstract"},{"comment":"The notation is inconsistent: σ_ac/σ_dc is written as 'sac/sdc', ω_H as 'wH', and the y-axis labels in Figs. 4–6 use 'log sac' without subscripts. Please unify mathematical notation in text and figures.","section":"Throughout"},{"comment":"The legend shows only 513 K and 553 K, but the text implies a broader temperature range. Please indicate all temperatures or state that only two are shown for clarity.","section":"Figs. 3(b–d)"},{"comment":"The Arrhenius plots have axis labels that could be clearer, and the caption text for BST uses '1.2 eV' while the text uses '0.12 eV.' Check and correct.","section":"Fig. 7"},{"comment":"There are typographical errors such as 'Arhennius' and inconsistent use of 'poycrystalline' vs 'polycrystalline.' A careful proofread is needed.","section":"General"}],"recommendation":"major_revision","confidential_remarks":"The core issue is that the TTSP evidence is largely circular given Eq. (2), and the CST non-collapse is explained by the two-process spectrum already invoked in the text. If the authors can supply n(T), fit residuals, and an independent scaling test (e.g., using modulus-derived relaxation frequencies or a two-process model for CST), the manuscript could become publishable. If not, the claims about 'dipolar frustration' and glassy dynamics should be substantially softened. The paper's novelty rests entirely on this scaling analysis, so the revision is essential."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThe new thing in this paper is the observation that, in the A2SmTaO6 series, the most distorted compound (CST) does not collapse onto the conductivity master curve while BST and SST do. The impedance data look genuine and the materials characterization is reasonable. The writing is clear.\n\nBut the interpretation does not hold. The BST/SST collapse is an algebraic consequence of their Eq. (2): if you fit σac = σdc[1 + (ω/ωH)^n] and n is constant, then σac/σdc is automatically a function of ω/ωH. They never report n(T) or fit residuals, so there is no way to tell a physical master curve from a mathematical restatement. The σdc–ωH correlation is also between two fit parameters, so it is not an independent check. For CST, the non-collapse is explained by the authors themselves as a two-process spectrum (grain boundary relaxation plus grain transport), so the deviation is expected without any 'dipolar frustration.' The leap to electrical glassiness is not backed by independent evidence.\n\nSmaller issues: the activation energy for BST is 0.12 eV in the text but 1.2 eV in Figure 7; the abstract lists A = Ba, Ca, leaving out Sr. These look like fixable typos.\n\nNet: a solid dataset with an overinterpreted central claim. I would send it to referees because the data and the CST observation are worth a serious look, but the authors need to report n(T), show the fit quality, and reframe the conclusions to avoid claiming a disorder probe. As it stands, this is a cautionary example of scaling analysis where the collapse is built into the fitting form.\n\nBring it to the reading group if you want to discuss how circular scaling claims can be.\n\nBest,","headline":"The paper adds new impedance data on three A2SmTaO6 perovskites, but the headline scaling collapse is an algebraic consequence of the fitting equation; the CST deviation is real but overinterpreted as 'dipolar frustration.'","tokens_in":10633,"tokens_out":6225,"would_cite":false,"duration_ms":66706,"reading_group":"maybe","serious_thinker":"no","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"For A2SmTaO6 double perovskites, the paper shows that conductivity spectra collapse onto a single master curve for Ba and Sr but not for Ca, and interprets the failure as evidence of dipolar frustration and glassy charge dynamics in the gra","keywords":["Scaling","Electrical conductivity","Impedance spectroscopy","Frustration","Disorder","Double perovskite","Time-temperature superposition"],"falsifier":"Fit Eq. (2) separately at each temperature and plot n versus T for BST, SST, and CST. If n changes systematically with temperature, then the reported sigma_ac/sigma_dc master curves are a trivial consequence of the fitting form rather than evidence of time–temperature superposition; if n is constant and CST's high-frequency branch still fails to merge with the other two compounds, the disorder/dipolar-frustration interpretation is supported. A second check: extract omega_H independently from the impedance modulus peaks and redo the scaling, rather than using omega_H from the same conductivity","tokens_in":9705,"feed_emoji":"⚡","tokens_out":6654,"duration_ms":69724,"temperature":0.7,"pith_summary":"The paper sets out to show that the way ac conductivity spectra scale with temperature and frequency can reveal how disorder shapes charge transport in polycrystalline double perovskites. Using three A2SmTaO6 compounds (A = Ba, Sr, Ca), the authors find that Ba2SmTaO6 and Sr2SmTaO6 conductivity spectra collapse onto one master curve when normalized by dc conductivity and scaled by hopping frequency, while Ca2SmTaO6 does not collapse at high frequencies in the grain-boundary regime. That deviation is read as evidence that local inhomogeneities in the energy landscape create a broad distribution of relaxation times, an electrical analogue of spin-glass 'dipolar frustration.' The claimed payoff is that the extent of scaling collapse serves as a sensitive probe of microscopic disorder: the more complete the master curve, the more homogeneous the charge-transport pathways. If correct, the result gives materials scientists a direct spectroscopic test for transport disorder in functional oxides.","feed_headline":"Conductivity master curves hold for Ba and Sr double perovskites — not Ca","feed_subtitle":"For A2SmTaO6 ceramics, time–temperature superposition fails in Ca's grain boundaries, signaling a disordered energy landscape.","key_machinery":"The load-bearing object is the scaled conductivity spectrum: sigma_ac/sigma_dc = F(omega/omega_s), with the frequency axis rescaled by omega_s = sigma_dc T or omega_s = omega_H. F is the temperature-independent master function; when all temperatures fall on one F, the time–temperature superposition principle holds. The argument also rests on the Jonscher power-law form sigma_ac = sigma_dc[1+(omega/omega_H)^n], which defines the hopping frequency omega_H marking the transition from long-range translation to dispersive hopping, and on the analogous scaling of the imaginary impedance Z''/Z''_max versus omega/omega_max. The machinery works by comparing the degree of collapse: complete collapse i","core_discovery":"The central claim is that the time–temperature superposition principle holds predominantly in the grain-boundary regime of these oxides, and that even there the quality of the collapse tracks microscopic energetic inhomogeneity. Concretely, the paper reports that for Ba2SmTaO6 and Sr2SmTaO6 the normalized ac conductivity sigma_ac/sigma_dc plotted against omega/omega_s (with omega_s = sigma_dc T or omega_s = omega_H) collapses onto a single temperature-independent master curve; for Ca2SmTaO6 the scaled spectra fail to merge in the high-frequency region beyond omega_H, where grain-boundary relaxation and long-range grain conduction both contribute. The authors also find a nearly linear (slope","pith_inferences":["A decisive check the paper leaves implicit: report the power-law exponent n(T). Because Eq. (2) makes sigma_ac/sigma_dc = 1+(omega/omega_H)^n, a temperature-independent n by construction gives a master curve; the interpretation would be much stronger if n is shown to be truly constant while CST still fails to scale.","If dipolar frustration is real, the same samples should show corresponding anomalies in dielectric loss scaling and in the frequency dependence of the electric modulus — measurements that are already in the paper's impedance data and could be analyzed with the same master-curve logic.","The spin-glass analogy suggests a testable prediction: quenched disorder should produce a frequency-dependent freezing-like feature in the AC susceptibility analogue (e.g., a peak in the imaginary modulus that shifts with frequency), comparable to T_f cusps in spin glasses.","The scaling protocol could be applied to single crystals or epitaxial films of the same compositions; if the collapse improves when grain boundaries are removed, that would confirm the grain-boundary landscape as the source of the non-universality."],"forward_implications":["If the scaling interpretation is right, ac conductivity measurements alone can rank the degree of transport disorder in polycrystalline oxides: the more complete the master-curve collapse, the more homogeneous the energy landscape.","The sigma_dc–omega_H correlation with near-unity slope implies that in these materials the onset of ac dispersion coincides with the relaxation frequency, so a single timescale governs both conduction and relaxation.","For Ca2SmTaO6, the failure to collapse above omega_H localizes the disorder to the grain-boundary regime and to the crossover where grain-boundary relaxation and grain conduction mix.","Activation energies in the 0.12–0.24 eV range support small-polaron hopping as the dominant transport mechanism, linking structural distortion (Sr, Ca monoclinic tilting) to slower dynamics.","The method carries over directly to other 1:1 ordered double perovskites: a composition-dependent scaling function (as previously used for Ba2HoRu1−xSbxO6) can extend the single-material master curves to solid-solution series."],"supporting_citations":[{"why":"Jonscher's power-law and jump-relaxation model supplies Eq. (2), which defines sigma_dc, omega_H, and the exponent n used throughout.","marker":"[13, 14]"},{"why":"Dyre and Schrøder's universality work motivates why ac conduction spectra in disordered solids should be expected to collapse onto a master curve.","marker":"[22]"},{"why":"Prior scaling study on A2HoRuO6 double perovskites establishes the time–temperature superposition method and the grain versus grain-boundary distinction the paper builds on.","marker":"[23]"},{"why":"Summerfield provides the sigma_dc T scaling formalism used for the frequency axis.","marker":"[24]"},{"why":"Ghosh and Pan supply the omega_H scaling formalism for conductivity spectra.","marker":"[25]"},{"why":"Ghosh and Sural provide a second, independent demonstration of omega_H scaling used to test the collapse.","marker":"[26]"},{"why":"The composition-dependent scaling study in Ba2HoRu1−xSbxO6 serves as the template for using scaling deviations to infer disorder effects.","marker":"[27]"},{"why":"Prior structural and dielectric characterization of A2SmTaO6 supplies the crystal structures, synthesis route, and baseline dielectric response used in the interpretation.","marker":"[29]"},{"why":"XPS and electronic-structure work links band gap and Ta–O hybridization to the conductivity trends across Ba, Sr, and Ca.","marker":"[30]"},{"why":"Polaron-hopping analysis in related A2LuTaO6 compounds supports the activation-energy interpretation in the present samples.","marker":"[31]"}],"fun_headline_variants":["Master curves collapse for Ba, Sr but not Ca in double perovskites","Ca breaks conductivity master curve in A2SmTaO6","Time-temperature superposition fails for Ca grain boundaries","Ba and Sr show universal ac conductivity scaling, Ca doesn't"],"cache_read_input_tokens":2688,"weakest_assumption_plain":"The load-bearing premise is that the collapse of the normalized spectra is a genuine test of universality and not an automatic consequence of the fitting form: this requires the power-law exponent n to be temperature-independent, a quantity the paper never reports.","fun_headline_variants_meta":{"raw":{"variants":["Master curves collapse for Ba, Sr but not Ca in double perovskites","Ca breaks conductivity master curve in A2SmTaO6","Time-temperature superposition fails for Ca grain boundaries","Ba and Sr show universal ac conductivity scaling, Ca doesn't"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000981,"raw_usage":{"total_tokens":3997,"prompt_tokens":738,"completion_tokens":3259,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":482,"completion_tokens_details":{"reasoning_tokens":3190}},"tokens_in":482,"tokens_out":3259,"duration_ms":25273,"temperature":1.0,"reasoning_tokens":3190,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-05T14:06:32.756569+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Fit Eq. (2) separately at each temperature and plot n versus T for BST, SST, and CST. If n changes systematically with temperature, then the reported sigma_ac/sigma_dc master curves are a trivial consequence of the fitting form rather than evidence of time–temperature superposition; if n is constant and CST's high-frequency branch still fails to merge with the other two compounds, the disorder/dipolar-frustration interpretation is supported. A second check: extract omega_H independently from the impedance modulus peaks and redo the scaling, rather than using omega_H from the same conductivity","supporting_citations":[{"cited_title":"Universality of ac conduction in disordered solids","cited_arxiv_id":null,"evidence_quote":"Dyre and Schrøder's universality work motivates why ac conduction spectra in disordered solids should be expected to collapse onto a master curve."},{"cited_title":"Time– temperature superposition in the grain and grain bound- ary response regime of a 2 horuo 6 (a= ba, sr, ca) double perovskite ceramics: a conductivity spectroscopic analy- sis","cited_arxiv_id":null,"evidence_quote":"Prior scaling study on A2HoRuO6 double perovskites establishes the time–temperature superposition method and the grain versus grain-boundary distinction the paper builds on."},{"cited_title":"Universal low-frequency behaviour in the ac hopping conductivity of disordered systems","cited_arxiv_id":null,"evidence_quote":"Summerfield provides the sigma_dc T scaling formalism used for the frequency axis."},{"cited_title":"Scaling of the conductivity spectra in ionic glasses: dependence on the structure","cited_arxiv_id":null,"evidence_quote":"Ghosh and Pan supply the omega_H scaling formalism for conductivity spectra."},{"cited_title":"Conductivity spectra of sodium fluorozirconate glasses","cited_arxiv_id":null,"evidence_quote":"Ghosh and Sural provide a second, independent demonstration of omega_H scaling used to test the collapse."},{"cited_title":"Exploring the intricacies in the conduction mechanism of the perovskite series ba2hosb1- xruxo6: A conductivity scaling approach","cited_arxiv_id":null,"evidence_quote":"The composition-dependent scaling study in Ba2HoRu1−xSbxO6 serves as the template for using scaling deviations to infer disorder effects."},{"cited_title":"Dielectric relaxation and collective vibrational modes of double-perovskites a 2 smtao 6 (a= ba, sr and ca)","cited_arxiv_id":null,"evidence_quote":"Prior structural and dielectric characterization of A2SmTaO6 supplies the crystal structures, synthesis route, and baseline dielectric response used in the interpretation."},{"cited_title":"X-ray photoelectron spectroscopic study and electronic structure of double-perovskites a2smtao6 (a= ba, sr, ca)","cited_arxiv_id":null,"evidence_quote":"XPS and electronic-structure work links band gap and Ta–O hybridization to the conductivity trends across Ba, Sr, and Ca."},{"cited_title":"Electronic structure and electrical conduction by polaron hopping mechanism in a2lutao6 (a= ba, sr, ca) double perovskite oxides","cited_arxiv_id":null,"evidence_quote":"Polaron-hopping analysis in related A2LuTaO6 compounds supports the activation-energy interpretation in the present samples."}],"review_version":1}