Alternative origins of polarity in compressively strained SrTiO3-RENiO3 capacitors

Alexander Lione; C\'esar Mag\'en; Evgenios Stylianidis; Felix Risch; Igor Stolichnov; Jorge \'I\~niguez-Gonz\'alez; Jos\'e A. Pardo; Laura Hechler; Nicholas C. Bristowe; Panagiotis Koutsogiannis

arxiv: 2605.29499 · v1 · pith:LNNPC7LNnew · submitted 2026-05-28 · ❄️ cond-mat.mtrl-sci

Alternative origins of polarity in compressively strained SrTiO3-RENiO3 capacitors

Evgenios Stylianidis , Panagiotis Koutsogiannis , Alexander Lione , Felix Risch , Laura Hechler , Igor Stolichnov , Jorge \'I\~niguez-Gonz\'alez , Jos\'e A. Pardo

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Nicholas C. Bristowe C\'esar Mag\'en Pavlo Zubko

This is my paper

Pith reviewed 2026-06-29 06:46 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci

keywords strained SrTiO3polarityinternal fieldscharge discontinuitiesnickelate electrodesferroelectric hysteresisepitaxial capacitors

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The pith

Observed polarity in compressively strained SrTiO3 capacitors stems from inhomogeneous internal fields rather than ferroelectricity.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper examines highly strained epitaxial SrTiO3 layers in capacitors using rare earth nickelate electrodes. Measurements show butterfly-shaped capacitance-voltage hysteresis and domain-like electromechanical responses that resemble ferroelectric behavior. However, the overall temperature-dependent electrical properties and piezoresponse force microscopy results are inconsistent with a stable ferroelectric state. The authors propose that the polarity arises instead from spatially inhomogeneous internal fields generated by charge discontinuities at the interfaces between formally charged nickelate layers and charge-neutral SrTiO3 layers, as supported by first-principles calculations.

Core claim

The polarity observed in these SrTiO3-RENiO3 structures is explained by spatially inhomogeneous internal fields due to charge discontinuities between the NdNiO3 and SrTiO3 layers, rather than by a stable ferroelectric polarization in the strained SrTiO3.

What carries the argument

Spatially inhomogeneous internal fields arising from charge discontinuities at the interfaces between charged rare-earth nickelate layers and neutral SrTiO3 layers.

If this is right

The apparent ferroelectric-like hysteresis can be produced by internal fields without requiring switchable spontaneous polarization.
Similar interface charge effects may influence polarity in other oxide heterostructures.
Room-temperature out-of-plane polarity in compressively strained SrTiO3 can be achieved through electrode design without needing true ferroelectricity.
First-principles calculations can predict such internal fields from the formal charges of the layers.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

This mechanism could be tested in other combinations of charged and neutral oxide layers to engineer polarity.
If confirmed, it may redirect efforts away from achieving bulk-like ferroelectricity in SrTiO3 towards interface engineering.
Variable-temperature measurements could be applied to distinguish internal field effects from ferroelectricity in other candidate materials.

Load-bearing premise

The variable-temperature electrical measurements and room-temperature piezoresponse force microscopy results are inconsistent with a stable ferroelectric state.

What would settle it

Observation of a stable, temperature-independent switchable polarization with clear Curie temperature behavior would falsify the internal field explanation.

read the original abstract

Since its original prediction 25 years ago, room-temperature out-of-plane ferroelectricity in compressively strained SrTiO3 remains an ongoing pursuit. In this work, we investigate the structural, electrical and electromechanical properties of highly strained epitaxial SrTiO3 capacitors with rare earth nickelate electrodes. The SrTiO3 layers experience compressive strains up to -3% and exhibit pronounced tetragonality, comparable to that of bulk PbTiO3. Variable-temperature electrical measurements and room-temperature piezoresponse force microscopy reveal butterfly-shaped capacitance-voltage hysteresis and domain-like electromechanical response typical of ferroelectric materials. However, the overall behavior is inconsistent with a stable ferroelectric state. We therefore propose an alternative mechanism for the observed polarity in our samples based on spatially inhomogeneous internal fields. Our first-principles calculations show that such fields may arise from charge discontinuities between the formally charged NdNiO3 layers and charge-neutral SrTiO3 layers.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The paper shows new measurements on highly strained STO with nickelate electrodes that look ferroelectric but argues the behavior fits better with internal fields from interface charge discontinuities, supported by DFT; the exclusion of true ferroelectricity is the key step that needs scrutiny.

read the letter

The core takeaway is that these compressively strained SrTiO3 layers in RENiO3 capacitors produce butterfly C-V loops and domain-like PFM signals, yet the temperature-dependent electrical data do not match what a stable ferroelectric state should show. The authors instead attribute the polarity to inhomogeneous internal fields created by charge discontinuities between the charged nickelate planes and neutral STO, and their first-principles calculations confirm such fields are possible.

What stands out is the specific choice of rare-earth nickelate electrodes and the high compressive strains (up to -3%), which produce strong tetragonality. The DFT work directly links the formal charges in NdNiO3 to the resulting fields without obvious fitting parameters, and the experimental structures are new enough to test this interface mechanism in a regime where ferroelectricity has been debated for years.

The measurements themselves are the main limitation. The abstract states the overall behavior rules out stable ferroelectricity, but it does not detail quantitative benchmarks such as expected remanent polarization decay with temperature or direct comparison to a Landau model for -3% strained STO. If the full paper supplies those explicit mismatches, the alternative explanation gains weight; without them the claim rests on qualitative assessment.

This work is aimed at groups studying oxide heterostructures and interface-driven polarity in thin films. It is worth sending to peer review because the question remains open and the calculations provide a concrete, testable alternative that can be checked against the data.

Referee Report

1 major / 1 minor

Summary. The manuscript examines the structural, electrical, and electromechanical properties of highly compressively strained epitaxial SrTiO3 layers (up to -3%) in capacitors with rare earth nickelate electrodes. It reports pronounced tetragonality, butterfly-shaped C-V hysteresis, and domain-like PFM responses. However, the authors conclude that the overall behavior across variable-temperature electrical measurements and room-temperature PFM is inconsistent with a stable ferroelectric state. They propose an alternative mechanism based on spatially inhomogeneous internal fields arising from charge discontinuities between formally charged NdNiO3 layers and charge-neutral SrTiO3 layers, supported by first-principles calculations.

Significance. If the inconsistency with stable ferroelectricity is rigorously established, the work would be significant for offering an alternative to the long-pursued room-temperature ferroelectricity in compressively strained SrTiO3. The first-principles calculations of charge discontinuities provide a parameter-free basis for the proposed internal fields, which is a clear strength of the approach.

major comments (1)

[Abstract / variable-temperature electrical measurements] Abstract: the claim that 'the overall behavior is inconsistent with a stable ferroelectric state' is load-bearing for the central argument, yet the manuscript provides no explicit quantitative criteria (e.g., expected remanence, coercive-field temperature scaling, or comparison against a Landau-Devonshire model for -3% strained SrTiO3) that would falsify a ferroelectric interpretation of the butterfly C-V and domain-like PFM data. Without such criteria, the exclusion of ferroelectricity cannot be evaluated.

minor comments (1)

[Abstract] The abstract refers to 'rare earth nickelate electrodes' generally but invokes NdNiO3 specifically for the charge-discontinuity mechanism; clarify the scope of the electrode materials studied.

Simulated Author's Rebuttal

1 responses · 0 unresolved

We thank the referee for their careful reading of the manuscript and for identifying this important point about the load-bearing claim in the abstract. We address the comment in detail below.

read point-by-point responses

Referee: [Abstract / variable-temperature electrical measurements] Abstract: the claim that 'the overall behavior is inconsistent with a stable ferroelectric state' is load-bearing for the central argument, yet the manuscript provides no explicit quantitative criteria (e.g., expected remanence, coercive-field temperature scaling, or comparison against a Landau-Devonshire model for -3% strained SrTiO3) that would falsify a ferroelectric interpretation of the butterfly C-V and domain-like PFM data. Without such criteria, the exclusion of ferroelectricity cannot be evaluated.

Authors: We agree that the exclusion of a stable ferroelectric state requires more explicit quantitative grounding. In the revised manuscript we will add a new subsection (and a brief expansion in the abstract) that (i) recalls the Landau-Devonshire predictions for out-of-plane ferroelectricity in SrTiO3 under –3 % compressive strain, (ii) states the expected temperature scaling of the coercive field and remanent polarization, and (iii) directly compares these expectations with the measured temperature-independent butterfly loops and the absence of any dielectric anomaly up to 400 K. These additions will make the falsification criteria explicit and allow the reader to evaluate the claim quantitatively. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation rests on independent first-principles calculations

full rationale

The paper's proposed mechanism for polarity relies on first-principles calculations demonstrating charge discontinuities at NdNiO3/SrTiO3 interfaces, which are independent of the experimental electrical and PFM data. The claim of inconsistency with stable ferroelectricity is presented as an empirical observation from variable-temperature measurements rather than a fitted or self-defined quantity. No steps reduce predictions to inputs by construction, no load-bearing self-citations are invoked for uniqueness theorems, and no ansatz is smuggled via prior work. The derivation chain is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Based solely on the abstract, the central claim rests on standard assumptions about perovskite charge neutrality and the validity of DFT for modeling interface fields; no free parameters or new entities are introduced in the provided text.

axioms (1)

domain assumption First-principles calculations accurately capture charge discontinuities and resulting internal fields at nickelate-STO interfaces.
The paper invokes these calculations to demonstrate the origin of the inhomogeneous fields.

pith-pipeline@v0.9.1-grok · 5758 in / 1379 out tokens · 21946 ms · 2026-06-29T06:46:40.732215+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

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