Thermal-expansion flexoelectric thermopolarization

The exact composition has been observed but not converted: Iwakiri, Miyata & Mori 2026 impose a temperature gradient whose thermal expansion produces a strain gradient whose flexoelectric polarization is detected (voltage and displacement current) in eight centrosymmetric insulators, scaling with the expansion coefficient — every mechanism in order, no electrical work delivered. Nothing in the OpenAlex runs or the two chases puts a load on such a device; the thermal-flexoelectric literature otherwise concerns the converse effect, bending-imposed gradients, uniform-temperature conduction effects and flexo-induced pyroelectricity. Inconclusive as a route search until the Scholar and Semantic Scholar runs exist; the open question is now narrow: has anyone extracted work. After the second reader's review (pass 24) the composition is recorded as the observed pathway pathway:thermal-expansion-flexoelectric-response — status observed, observed_through the flexoelectric charge step, the final conversion to work unsupported — and the route reads observed · output not delivered while its class stays candidate. The reviewer's nearest additional hit, Han et al. 2026 (a heat-driven flexoelectric nanogenerator whose differential thermal deformation supplies the strain gradient; current response only in the accessible record), stays insufficient-information pending its full text. The composite-name form (pass 27) then surfaced what the decomposed forms could not: thermopolarization currents measured in dielectrics from 1982 (Kholkin, Trepakov & Smolenskii), in SrTiO₃, KTaO₃ and KH₂PO₄ by 1989 (Trepakov, Nurieva & Tagantsev, who separated a 'proper' non-flexoelectric thermopolarization from the flexoelectric 'tertiary pyroeffect'), and dynamically in relaxor paraelectrics by 1994 — polarization observed under a temperature gradient decades before the 2026 preprint, still with no load; the second reader's ruling (pass 28) made the direct effect its own phenomenon and coupling family, so those measurements are evidence for it and wrong-coupling here; Iwakiri's α-scaling supports attributing their dominant measured component to the flexoelectric chain without excluding a direct residual.

• Observation of universal thermopolarization effect in insulators (2026) · sink variant · arXiv:2605.17224 (Iwakiri, Miyata & Mori, NIMS, 17 May 2026; not yet in OpenAlex, found through the reviewer and confirmed on arXiv), read in full. An on-chip heater driven at 1 kHz imposes a temperature gradient (about 0.5 K modulation) across 0.25–1 mm substrates; the non-uniform thermal expansion's strain gradient produces an out-of-plane flexoelectric polarization detected as a second-harmonic voltage and, more quantitatively, as the screening (displacement) current in a detector electrode, in MgO, Al₂O₃, MnO, mica, PET, PEN, polyimide and soda-lime glass; the response scales with the coefficient of thermal expansion, is reproduced by finite-element thermo-mechanics, grows as 1/thickness and by over an order of magnitude at the glass and antiferromagnetic transitions. Driver, both mechanisms and their order are physically present; the sink is a measured polarization and its displacement current, not electrical work delivered to a load, so the route's recorded output is not demonstrated.
• Thermally Induced Flexo-Type Effects in Nanopatterned Multiferroic Layers (2020) · constituent only · Thermal expansion in a nanopatterned array of ferromagnetic nanocylinders in a ferroelectric polymer produces giant strain gradients at moderate temperatures that depolarise the ferroelectric via the flexoelectric effect (and change the magnetisation flexomagnetically), with finite-element support — the thermal-expansion → strain-gradient → flexoelectric handoff observed, no electrical output (abstract read on OpenAlex).
• Thermal gradient induced flexoelectric effects in bulk Ba0.67Sr0.33TiO3 (2016) · wrong coupling · The converse effect: a temperature gradient along symmetric BST bars produces an electric-field gradient through the temperature-dependent permittivity, and the strain that gradient induces is measured — field gradient → strain, the reverse of the route's strain gradient → polarization (abstract read on OpenAlex).
• Strain gradient induced thermal-electrical response in paraelectric Na0.5Bi0.5TiO3-based ceramics (2018) · wrong driver · A pyroelectric-like temperature-dependent current appears in paraelectric NBT ceramics under bending deformation, attributed to flexoelectrically induced conduction; the strain gradient is imposed mechanically, not by thermal expansion (abstract read on OpenAlex).
• Large Thermal–Electrical Response and Rectifying Conduction Behavior in Asymmetrically Reduced Ferroelectric Ceramics (2019) · wrong driver · Thermal-electrical conversion 'in a uniform temperature environment' from a reduction-induced built-in field and conductivity in NBT ceramics (0.18 mW/cm³ claimed): no temperature gradient and no thermal-expansion strain gradient; the driver and the mechanism are not the route's (abstract read on OpenAlex).
• Enhancement of thermal-electrical like response by flexoelectric effect in sodium bismuth titanate bilayer ceramics with compositional inhomogeneity (2023) · insufficient information · A bilayer NBT ceramic whose compositional gradient and differing thermal expansion leave a sintering strain gradient; a 'thermal-electrical like response' larger than the single layer's is attributed to a flexoelectric-like built-in potential coupled with conductivity. Whether an imposed temperature gradient drives a thermal-expansion strain gradient in operation, and what output is measured, cannot be settled from the abstract (Springer page).
• Flexo-Pyroelectric Effect (2025) · wrong driver · A strain gradient imposed by an AFM tip gives centrosymmetric SrTiO₃ a pyroelectric coefficient under temperature fluctuations — the strain gradient is mechanical and the driver a temperature change in time, not a gradient's thermal expansion (abstract read on OpenAlex).
• Thermal excitation of flexoelectricity in silicon (2025) · constituent only · The flexoelectric coefficient of intrinsic and doped silicon measured from −50 to 200 °C (15.2 nC/m to 1.8 μC/m in intrinsic Si): a material property of the second mechanism, no thermal-expansion drive and no output (abstract read on OpenAlex).
• Temperature Gradient Introduced Ferroelectric Self-Poling in BiFeO3 Ceramics (2013) · constituent only · A sintering temperature gradient and its thermal strain separate bismuth and oxygen vacancies into defect dipoles whose internal field (> 10 kV/cm) poles the ceramic on cooling — a temperature gradient acting through thermal strain on polarization, but via defect dipoles rather than the flexoelectric effect, and with no output (abstract read on OpenAlex).
• Pyroelectric, piezoelectric, flexoelectric, and thermal polarization effects in ionic crystals (1987) · theory only · Tagantsev's review including the thermal-polarization prediction the 2026 preprint tests; theory (title and the preprint's citation of it).
• Dual-Mode Flexoelectric Nanogenerators Activated by Light and Heat for Broad-Spectral Photodetection and Thermal Response (2026) · insufficient information · Experimental heat-driven flexoelectric nanogenerator (Han et al. 2026, Adv. Funct. Mater.): under temperature variation the heterojunction components deform differentially, the interfacial strain gradient drives flexoelectric polarization and a measured current (effective pyroelectric coefficient up to 7518 μC m⁻² K⁻¹). The accessible record does not establish electrical work delivered to a load, and whether the imposed thermal field is the route's spatial temperature gradient (rather than a temperature change with a coefficient-of-expansion mismatch) must be checked in the full text, which is paywalled — an owner read is requested. If the full text confirms the driver and still reports no load: sink-variant; if it reports load power attributable to thermal-mode flexoelectric generation, it may supersede Iwakiri 2026 as the qualifying hit.
• Exact solutions for thermally induced electromechanical fields of PN junctions in centrosymmetric semiconductors (2024) · theory only · Wei et al. 2024 (J. Appl. Phys.) define the thermoflexoelectric effect — temperature gradients generate inhomogeneous strains and induce flexoelectric polarizations — and solve a one-dimensional PN-junction model; theory, no experiment, no output. Its name for the composition is now an alias of the flexoelectric effect.
• Flexoelectric polarization induced by inhomogeneous heating and implications for energy harvesting (2019) · theory only · Yurkov, Dejneka & Yudin 2019 (Int. J. Solids Struct.): a variational theory of the polarization of an inhomogeneously heated thin plate, with a calculated waste-heat-to-electricity bound of up to tens of watts per kilogram of flexoelectric material; theory, no device — a citation-chase seed for the next sitting.
• Recent developments of the thermopolarization effect investigation (1989) · wrong coupling · Trepakov, Nurieva & Tagantsev 1989 (Ferroelectrics 94, 377–381): the thermopolarization effect measured in centrosymmetric SrTiO₃ and KTaO₃ and in piezoelectric KH₂PO₄ single crystals 'in spite of the tertiary pyroeffect competition', with criteria separating a 'proper' (non-flexoelectric) thermopolarization from the flexoelectric contribution — it explicitly distinguishes its response from the thermal-expansion → flexoelectric chain this route spells, so it is evidence for the atlas's direct thermopolarization effect (recorded in pass 28), not for this route.
• Thermopolarization currents in dielectrics (1982) · wrong coupling · Kholkin, Trepakov & Smolenskii 1982 (JETP Letters 35, 124–127; read in full from the archive): thermopolarization currents in centrosymmetric PMN under an end-to-end temperature difference, linear in d(ΔT)/dt and reversing with ∇T, B₁₁ ≈ 3 × 10⁻¹² C/(cm·K) — attributed to Gurevich's direct thermopolarization effect, with no thermal-expansion strain-gradient mechanism considered; evidence for the direct effect (status reported until its separation from the flexoelectric contribution is read), not for this route.
• Frequency and temperature dependence of the thermopolarization response in dynamic investigations (1994) · wrong coupling · Rafikov, Savinov, Jastrabík & Trepakov 1994 (phys. stat. sol. (a) 144): the dynamic thermopolarization response of paraelectric PbNi₁/₃Nb₂/₃O₃ and PbMg₁/₃Nb₂/₃O₃ measured in low- and high-frequency regimes (∝ ω^½ and ω^−½), the low-frequency response inversely proportional to thickness — the predicted behaviour of the direct thermopolarization effect, without establishing the thermal-expansion → strain-gradient → flexoelectric chain; evidence for the direct effect, not for this route.
• Theory of Thermopolarization Effect (2025) · theory only · Onishi, Isobe, Shitade & Nagaosa 2025 (Nano Letters): the polarization response of an insulator to a temperature gradient described through the free-energy response to an electric-field gradient (the Q tensor), with a generalized Mott relation and an analogy to the anomalous Hall and Nernst effects — a direct thermopolarization theory that does not go through thermal expansion.
• Electric polarization in crystals and its response to thermal and elastic perturbations (1991) · review only · Tagantsev 1991 (Phase Transitions): pyroelectricity, piezoelectricity, flexoelectricity and the thermopolarization effect (polarization response to a temperature gradient) on one theoretical footing; the definitions, not an experiment.
• Reverse thermopolarization effects in dielectrics (1995) · wrong coupling · Trepakov, Rafikov, Marvan, Savinov & Jastrabík 1995 (Ferroelectrics Letters): the converse — a temperature difference of ≈ 10⁻⁴ K appearing across a PMN capacitor charged at 10⁶ V/m, read as a 'dielectric Peltier effect'; the reverse direction of the route.
• On-chip detection of anisotropic thermopolarization in quartz (2026) · wrong coupling · Physical Review Research, 14 September 2026 (Crossref lists no authors or abstract): the companion to Iwakiri 2026 on piezoelectric quartz, where by the second reader's reading (pass 24) the thermal stress feeds piezoelectric rather than flexoelectric polarization — a different coupling, to be read when accessible.
• Antisymmetric thermopolarization by electric toroidicity (2022) · theory only · Nasu & Hayami 2022 (Phys. Rev. B 105, 245125): the thermopolarization tensor's antisymmetric part from electric toroidicity — theory of the direct effect, not this route.
• Size-dependent analysis of thermoelastic damping in thermoflexoelectric nanobeam resonators (2026) · theory only · Acta Mechanica 2026: a thermoflexoelectric nanobeam damping model, by title.

4378 indexed works reported across the queries, 158 unique retrieved; nobody has read them for a qualifying demonstration. A person can screen this frozen list and promote it to a reviewed record without re-running the query.

• OAdriver-mechanism:12185 reported · 100 retrieved
• OAdriver-mechanism:12185 reported · 50 retrieved
• OAmechanism-pair:1-28 reported · 8 retrieved
• OAwhole-chain0 reported · 0 retrieved
• OAdemonstration-precision0 reported · 0 retrieved

Planned runs NOT run in this bundle (engine unavailable): search:2026-09-21-p-a093d7ecc5/s2-dm1 (semantic-scholar); search:2026-09-21-p-a093d7ecc5/s2-mp12 (semantic-scholar); search:2026-09-21-p-a093d7ecc5/s2-wc (semantic-scholar); search:2026-09-21-p-a093d7ecc5/s2-dp (semantic-scholar).

4423 indexed works reported across the queries, 202 unique retrieved; nobody has read them for a qualifying demonstration. A person can screen this frozen list and promote it to a reviewed record without re-running the query.

• OAcomposite-name45 reported · 45 retrieved
• OAdriver-mechanism:12185 reported · 100 retrieved
• OAdriver-mechanism:12185 reported · 50 retrieved
• OAmechanism-pair:1-28 reported · 8 retrieved
• OAwhole-chain0 reported · 0 retrieved
• OAdemonstration-precision0 reported · 0 retrieved

Planned runs NOT run in this bundle (engine unavailable): search:2026-09-21-p-a093d7ecc5/s2-cn (semantic-scholar); search:2026-09-21-p-a093d7ecc5/s2-dm1 (semantic-scholar); search:2026-09-21-p-a093d7ecc5/s2-mp12 (semantic-scholar); search:2026-09-21-p-a093d7ecc5/s2-wc (semantic-scholar); search:2026-09-21-p-a093d7ecc5/s2-dp (semantic-scholar).