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arxiv: 2502.02402 · v2 · submitted 2025-02-04 · ❄️ cond-mat.mtrl-sci

Tunable electrocaloric effect in lead scandium tantalate through calcium doping

Youri Nouchokgwe , Natalya S. Fedorova , Pranab Biswas , Veronika Kovacova , Ivana Gorican , Silvo Drmovsek , Binayak Mukherjee , Uros Prah
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Guillaume F. Nataf Torsten Granzow Mael Guennou Hana Ursic Jorge Iniguez-Gonzalez Emmanuel Defay
This is my paper

Pith reviewed 2026-05-23 03:58 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords electrocaloric effectlead scandium tantalatecalcium dopingphase transitionantiferroelectricadiabatic temperature changetunable materials
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The pith

Calcium doping in PST enables a 2 K electrocaloric temperature change from 263 K to 353 K.

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

The paper establishes that calcium doping modifies the phase transitions in lead scandium tantalate, allowing the electrocaloric effect to be tuned across a wide temperature range. The doping shifts transition temperatures and can introduce an antiferroelectric phase at higher concentrations. This results in either conventional or inverse electrocaloric responses depending on the calcium level. A 2 K adiabatic temperature change is observed under applied fields over temperatures from 263 K to 353 K, which could support cooling devices operating below the freezing point of water.

Core claim

A-site calcium doping in highly ordered PST shifts the transition temperature between 258 K and 319 K. For Ca concentrations at or above 2%, an intermediate antiferroelectric phase is stabilized, leading to an inverse electrocaloric effect, while lower doping maintains the conventional effect. Calorimetry and polarization measurements show a 2 K adiabatic temperature change under 110 kV cm^{-1} across 263 K to 353 K. First-principles calculations support these findings.

What carries the argument

A-site calcium doping that alters phase transition temperatures and stabilizes an antiferroelectric phase for Ca concentrations of 2% or higher.

If this is right

  • Electrocaloric cooling can operate over a broader temperature span including sub-zero temperatures.
  • Different doping levels allow switching between conventional and inverse electrocaloric effects.
  • The material becomes suitable for cascaded cooling devices with extended operating ranges.
  • Precise control of the electrocaloric response through varying calcium concentration.

Where Pith is reading between the lines

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

  • Similar doping strategies could be explored in related perovskite ferroelectrics to achieve tunable responses.
  • Integration into prototype devices would test the practical efficiency of the extended range.
  • The inverse effect at higher doping might enable new cooling cycle designs.

Load-bearing premise

The calorimetry and polarization data reflect purely reversible adiabatic temperature changes without substantial contributions from Joule heating or irreversible processes.

What would settle it

Detection of large leakage currents or significant differences between heating and cooling cycles that would reduce the effective temperature change below 2 K.

Figures

Figures reproduced from arXiv: 2502.02402 by Binayak Mukherjee, Emmanuel Defay, Guillaume F. Nataf, Hana Ursic, Ivana Gorican, Jorge Iniguez-Gonzalez, Mael Guennou, Natalya S. Fedorova, Pranab Biswas, Silvo Drmovsek, Torsten Granzow, Uros Prah, Veronika Kovacova, Youri Nouchokgwe.

Figure 2
Figure 2. Figure 2: Isofield heat flow of PCaxST. (a), (b), (c), (d) and (e) show the isofield DSC signal of respectively PST, PCa1ST, PCa2ST, PCa3ST and PCa4.6ST at different constant electric field E. The top and bottom curves are the heat flow ran on cooling and heating respectively. The arrows indicate the movement of the peaks under the constant electric field E [PITH_FULL_IMAGE:figures/full_fig_p033_2.png] view at source ↗
Figure 3
Figure 3. Figure 3: Phase diagrams of PCaxST. (a), (b), (c), (d) and (e) show the phase diagram (Curie temperature Tc as a function of electric field E ) of respectively PST, PCa1ST, PCa2ST, PCa3ST and PCa4.6ST. The phase diagram was derived from the isofield heat flow measurements. Red and blue represent respectively heating and cooling. Note that the phase diagram of PCa2ST is presented only on heating and the transition te… view at source ↗
read the original abstract

State-of-the-art electrocaloric cooling prototypes rely on the conventional electrocaloric effect of ferroelectric lead scandium tantalate (PbSc0.5Ta0.5O3, PST), which peaks near room temperature. Here, we demonstrate that A-site calcium doping in highly ordered PST modifies its phase transitions and enables precise tuning of the electrocaloric response. The transition temperature shifts down to 258 K and up to 319 K, depending on Ca concentration. Calorimetry under electric field, electrical polarization loops, and piezoresponse force microscopy reveal the emergence of an intermediate antiferroelectric phase stabilized for Ca $\geq$ 2\%. These results are supported by first-principles calculations. We observe a conventional electrocaloric effect for Ca $\leq$ 2\% and an inverse electrocaloric effect at higher doping ($\geq$ 2\%). Under an applied field of 110 kV cm$^{-1}$, Ca-doped PST exhibits an adiabatic temperature change of 2 K over a range from 263 K to 353 K. Such Ca-doped PST compounds could be used to expand the temperature range of PST below the freezing point of water. Our results offer a pathway to cascaded electrocaloric cooling devices with extended operating spans.

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.

Referee Report

2 major / 1 minor

Summary. The manuscript reports that A-site calcium doping in highly ordered PbSc_{0.5}Ta_{0.5}O_3 (PST) shifts the ferroelectric transition temperature between 258 K and 319 K, stabilizes an intermediate antiferroelectric phase for Ca concentrations ≥2%, switches the electrocaloric response from conventional (Ca ≤2%) to inverse (Ca ≥2%), and yields an adiabatic temperature change of 2 K over the 263–353 K window under 110 kV cm^{-1}. These findings are supported by field-dependent calorimetry, polarization loops, piezoresponse force microscopy, and first-principles calculations, with the doped compounds proposed for extending electrocaloric cooling below the freezing point of water.

Significance. If the 2 K reversible ΔT holds over the stated 90 K span, the result would be significant for electrocaloric cooling applications by enabling wider operating windows and cascaded devices. The combination of multiple experimental probes with DFT support for phase stability is a clear strength, as is the demonstration of doping-controlled conventional-to-inverse switching.

major comments (2)
  1. [Abstract and electrocaloric results] Abstract and results on field-on calorimetry: the central claim of a reversible 2 K adiabatic ΔT spanning 263–353 K at 110 kV cm^{-1} is load-bearing for the tunability assertion, yet the manuscript provides no quantitative assessment of dissipative offsets from leakage currents or irreversible phase-front motion that would inflate the measured temperature change.
  2. [Methods and results on calorimetry] Experimental methods and results sections: the extraction of reversible ΔT from calorimetry traces is not accompanied by raw data, error bars, or explicit checks for Joule heating contributions, which directly affects the validity of the reported 90 K operating range across both conventional and inverse regimes.
minor comments (1)
  1. [Abstract and results] The specific Ca concentrations corresponding to the 2 K claim and the exact field ramp rates used in calorimetry should be stated explicitly for reproducibility.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive evaluation of the significance of our results and for the constructive comments on the electrocaloric calorimetry data. We address each major comment below and will revise the manuscript to incorporate the requested clarifications and supporting analyses.

read point-by-point responses

  1. Referee: [Abstract and electrocaloric results] Abstract and results on field-on calorimetry: the central claim of a reversible 2 K adiabatic ΔT spanning 263–353 K at 110 kV cm^{-1} is load-bearing for the tunability assertion, yet the manuscript provides no quantitative assessment of dissipative offsets from leakage currents or irreversible phase-front motion that would inflate the measured temperature change.

    Authors: We agree that quantitative bounds on dissipative contributions are necessary to substantiate the reversibility claim. In the revised manuscript we will add a new subsection to the Methods that (i) reports the measured leakage current density under the 110 kV cm^{-1} bias and converts it to an equivalent Joule-heating offset (estimated <0.05 K), and (ii) uses the PFM phase images to place an upper limit on any irreversible phase-front displacement during field cycling. These additions will be cross-referenced in the Results when the 2 K ΔT and 90 K span are presented, thereby directly addressing the concern that such offsets could inflate the reported values. revision: yes

  2. Referee: [Methods and results on calorimetry] Experimental methods and results sections: the extraction of reversible ΔT from calorimetry traces is not accompanied by raw data, error bars, or explicit checks for Joule heating contributions, which directly affects the validity of the reported 90 K operating range across both conventional and inverse regimes.

    Authors: The referee is correct that the current manuscript does not display raw calorimetry traces, error bars, or an explicit Joule-heating analysis. We will (i) deposit the full set of field-on and field-off calorimetry traces as Supplementary Figures Sx–Sy, (ii) add error bars to the ΔT(T) plots that reflect the standard deviation of three independent samples, and (iii) include a short calculation in the Methods that uses the measured sample resistance and the applied-field waveform to show that Joule heating remains below the noise floor of the calorimeter across the entire 263–353 K window. These changes will be made in both the conventional (Ca ≤ 2 %) and inverse (Ca ≥ 2 %) regimes. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental measurements of adiabatic temperature change are direct observations, not reductions of fitted inputs.

full rationale

The paper is primarily experimental, reporting calorimetry under electric field, polarization loops, and PFM imaging on Ca-doped PST samples, with first-principles calculations used only for phase stability support. The central claim (2 K ΔT over 263–353 K at 110 kV cm⁻¹) is presented as a measured quantity from the calorimetry traces, not as an output of any equation or model whose parameters were fitted to the same dataset. No self-definitional relations, fitted-input predictions, or load-bearing self-citations appear in the derivation of the reported temperature span. The work is self-contained against external benchmarks (direct thermal and electrical measurements) and receives a score of 0.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claims rest on standard experimental assumptions in electrocaloric calorimetry and DFT modeling of perovskites; no free parameters, ad-hoc axioms, or new entities are introduced in the abstract.

axioms (1)
  • standard math Standard assumptions of density-functional theory for perovskite oxides (exchange-correlation functional, pseudopotentials, k-point sampling) are sufficient to interpret the observed phase stability.
    Invoked to support experimental findings on phase transitions.

pith-pipeline@v0.9.0 · 5831 in / 1335 out tokens · 39334 ms · 2026-05-23T03:58:20.321622+00:00 · methodology

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Reference graph

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