[EN] The direct integration of crystalline oxide layers into flexible electronic systems requires the development of relatively simple, low-temperature processing routes. Seeding represents a powerful strategy to reach this objective by the generation of preferential sites for the nucleation of crystalline phases with a reduced energy barrier. Here, a novel approach is reported where nanoseeds are generated in-situ from a precursor solution using a solvent-engineering strategy (solvent-antisolvent). The controlled addition of an antisolvent (1,3-propanediol) to a solution of metal salts (Bi/Fe) dissolved in acetic acid results in the formation of nanocrystals (seeds) by supersaturation. The presence of such nanoseeds is also confirmed in the deposited layers, improving significantly the crystallinity of the respective BiFeO3 thin films as complementary deduced by piezoresponse force microscopy. Using this low-temperature strategy, crystalline films are directly grown on flexible polymeric substrates at only 350 ºC showing a remanent polarization of 10.5 μC cm-2 and a clear photovoltaic effect (11.7 μW cm-2) of interest in computer memories and energy harvesters. The flexibility of the BiFeO3 thin films may enlarge the number of applications of this multifunctional, lead-free material in next-generation digital and sustainable electronic devices based on a facile, low-cost fabrication method with a reduced energy consumption., This work is part of the Spanish Projects PID2019-104732RB-I00 and MAT2017-91772-EXP funded by MCIN/AEI/10.13039/501100011033. Grant RYC-2016-20047 funded by MCIN/AEI/10.13039/501100011033. O. B. acknowledges financial support from Spanish "JAE Intro" Programme (JAEINT_19_01923)., Peer reviewed

Ferroelectric oxides with low bandgaps are mainly based on the BiFeO perovskite upon the partial substitution of iron with different cations. However, the structural stability of many of these perovskites is only possible by their processing at high pressures (HP, >1GPa) and high temperatures (HT, >700ºC). Preparation methods under these severe conditions are accessible to powders and bulk ceramics. However, transferring these conditions to the fabrication of thin films is a challenge, thus limiting their use in applications. Here, a chemical solution deposition method is devised, which overcomes many of these restrictions. It is based on the application of an external compressive-stress to the film sample during the thermal treatment required for the film crystallization, promoting the formation and stabilization of these HP perovskites. We demonstrate the concept on BiFeCrO (BFCO) thin films deposited on SrTiO (STO) substrates and with large chromium contents. The resulting BFCO perovskite films show narrow bandgaps (Eg∼2.57 eV) and an excellent ferroelectric response (remnant polarization, P∼ 40 μC cm). The polarized thin films under illumination present a large out-put power of ∼6.4 μW cm, demonstrating their potential for using in self-powered multifunctional devices. This stress-mediated solution deposition method can be extended to other perovskite films which are unviable under conventional deposition methods., This work has been financed by Spanish Projects PID2019-104732RB-I00, MAT2016-76851-R, MAT2017-91772-EXP (AEI/FEDER, UE) and RTI2018-096918-B-C41. I.B. acknowledges financial support from the Ramón&Cajal Spanish Programm. We thank Dr. M. Coll and P. Machado for the deposition of LSMO layers on the STO substrates (Instituto de Ciencia de Materiales de Barcelona ICMAB-CSIC). M.L.-C. and H.X. acknowledges the support from Spanish MINECO for the grant GraPErOs (ENE2016-79282-C5-2-R), the OrgEnergy Excellence NetworkCTQ2016-81911- REDT, the Agència de Gestiód'Ajuts Universitaris i de Recerca (AGAUR) for the support to the consolidated Catalonia research group 2017 SGR 329 and the Xarxa de Referència en Materials Avançats per a l'Energia (Xarmae). ICN2 is supported by the Severo Ochoa program from Spanish MINECO (Grant No. SEV-2017-0706) and is funded by the CERCA Programme / Generalitat de Catalunya., Peer reviewed

[EN] The (1 – x)BiFeO-xPbTiO (BFO-PTO) perovskite solid solution has great potential for being used in practical devices, as it exhibits significant ferroelectric response at its morphotropic phase boundary (MPB). However, the significant conduction, particularly high electrical leakage currents that BFO-PTO films show at room temperature, deteriorates their functionality. This is mainly associated with the presence of multivalent iron along with A-site and oxygen vacancies. Here, solution-derived BFO-PTO thin films have been crystallized at low temperature on Pt/TiO/SiO/Si substrates, by a rapid thermal annealing process to minimize Bi and Pb volatilization. X-ray analyses have revealed that textured films are obtained with a pseudocubic perovskite structure and without the formation of detectable second phases. Microstructural studies indicated a columnar growth of the films with grain size well above the nanometric range, which, therefore, should not produce an appreciable reduction of the ferroelectric response due to size effects. Because of the relatively low content of charged defects produced in these BFO-PTO films during processing, ferroelectric hysteresis loops can be measured at room temperature. The highest value of remnant polarizations (2P= 58 μC/cm) was obtained for the 0.65BiFeO-0.35PbTiO (65BFO-35PTO) films, which suggests that this film composition lies in the proximity of the MPB where the coexistence of a highly textured <100> tetragonal phase and a rhombohedral one seems to occur., Layiq Zia acknowledges the Higher Education Commission of Pakistan (HEC) for financial support for his stay at ICMM-CSIC under the Indigenous 5000-PhD Fellowship Program (PIN: 112-27186-2PS1-143) and the International Research Support Initiative Program (IRSIP) (PIN: IRSIP 43 PSc 48). Ricardo Jiménez, Iñigo Bretos, Harvey Amorín, Miguel Algueró, and M. Lourdes Calzada acknowledge the financial support of the Spanish Projects PID2019-104732RB-I00, MAT2017-88788-R, and MAT2017-91772-EXP. Iñigo Bretos acknowledges financial support from the Ramón & Cajal Spanish Program. GHJ acknowledges
financial support from the Pakistan Higher Education Commission (HEC, NRPU project number 8342).
Enrique Rodríguez-Castellón thanks project RTI2018-099668-BC22 of Ministerio de Ciencia, Innovación y Universidades, and FEDER funds.

[EN] We propose a disruptive method to process metal oxide thin films whereby hydroxyl radicals (˙OH) are photogenerated in situ from the atmosphere where the corresponding solution-deposited layers are UV-irradiated. The reaction of these radicals with the film results in the transformation of the deposited layer into a highly-densified amorphous metal-oxygen network that easily evolves to the crystalline film at much lower temperatures than those traditionally used (over 600 °C). An exhaustive study has allowed us to determine the underlying mechanisms involved in the accelerated crystallization of these oxides by the presence of ˙OH radicals during the process. We demonstrate that the method is applicable to all-solution metal oxide thin films, validating its general application in thin films of the binary BiO oxide and of more complex oxides like BiFeO and Pb(ZrTi)O ferroelectric perovskites. It is shown that the metal oxide crystallization occurs between 250 °C and 350 °C, a temperature range hundreds of degrees below their conventional processing temperatures and fully compatible with their direct growth on flexible polymer substrates. This processing method opens new opportunities for the integration of high-performance multifunctional oxide layers into the next-generation devices demanded today by emerging technologies such as flexible or wearable electronics., This work is part of the Spanish Project PID2019-104732RB-I00 funded by MCIN/AEI/10.13039/501100011033. I. B. acknowledges Grant RYC-2016-20047 funded by MCIN/AEI/10.13039/501100011033. A. Y. R. and S. L. acknowledge the financial support of CAM, PEJ-2019-AI/IND-13396 and PEJ-2020-AI/IND-18134., Peer reviewed

Exploiting the exceptional multiferroic characteristics of BiFeO3-based systems depends largely on controlling the high leakage currents that often constrain the ferroelectric response of this material. This limiting circumstance is even more restrictive in the film geometry, where the high area/volume ratio can add complications related to the uncontrolled loss of a particularly volatile element such as bismuth. In this work we address the suppression of such non-switching contribution by preparing BFO-BiT thin film composites and using a low-temperature processing protocol in a fully aqueous medium. With an adequate and systematic doping of both oxides, the produced composites show both magnetic and ferroelectric response at room temperature, in a process that is also related to the fine matching between the two crystal lattices involved. The results obtained further indicate the possibility of applying a simple, sustainable protocol with high scalability prospects to fabricate exploitable multiferroic systems, i.e. with no need for large energy inputs nor sophisticated equipment., This work was supported by the Spanish Ministry of Science, Innovation and Universities (MICINN) under the project MAT2016–80182-R. Also, this work is part of the Spanish Project PID2019–104732RB-I00, funded by MCIN/AEI/10.13039/501100011033. D. G. Calatayud also acknowledges the Fundación General CSIC (ComFuturo Program) for the financial support., Peer reviewed

Simple and cost-effective procedures for the direct integration of ferroelectric perovskite oxides into Ni structures are necessary to realize
related multifunctional metallic microelectromechanical systems, such as dual-source energy harvesters. This is especially difficult in the case
of lead-containing morphotropic phase boundary materials for high piezoelectric response because the two components are thermodynamically
incompatible and the formation of NiOx or perovskite oxide reduction takes place depending on the processing conditions. We show
here that low-temperature solution processing is an effective means to kinetically limit nickel oxidation, capable of providing BiFeO3–PbTiO3
films on Ni plates at only 500 ○C. Bulk-like ferroelectric properties and a distinctive magnetoelectric response were attained. This perovskite
system, not explored before on Ni, has a much larger switchable polarization than the widely studied Pb(Zr,Ti)O3, and it is shown here to
present an excellent downscaling behavior of ferroelectric properties until the verge of the nanoscale., This work was funded through the Spanish Projects TED2021-130871B-C21/AEI/10.13039/501100011033/Unión Europea Next-GenerationEU/PRTR, and PID2022-136790OB-I00 and PID2019-104732RB-I00, funded by MCIN/AEI/10.13039/501100011033. E.R.C. thanks the Spanish Ministry of Science and Innovation (PID2021-126235OB-C32, funded by MCIN/AEI/10.13039/501100011033/and FEDER funds, and TED2021-130756B-C31, MCIN/AEI/10.13039/501100011033, and “ERDF:
A way of making Europe” by the European Union NextGenerationEU/PRTR). L.Z. acknowledges the Higher Education Commission of Pakistan (HEC) for the financial support for his stay at ICMM-CSIC under the Indigenous 5000-PhD Fellowship Program(PIN: 112-27186-2PS1-143) and the International Research Support Initiative Program (IRSIP) (PIN: IRSIP 43 PSc 48).

Ferroelectric oxides with low bandgaps are mainly based on the BiFeO perovskite upon the partial substitution of iron with different cations. However, the structural stability of many of these perovskites is only possible by their processing at high pressures (HP,.