{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2025,10,12]],"date-time":"2025-10-12T02:29:19Z","timestamp":1760236159080,"version":"build-2065373602"},"reference-count":40,"publisher":"MDPI AG","issue":"21","license":[{"start":{"date-parts":[[2021,10,26]],"date-time":"2021-10-26T00:00:00Z","timestamp":1635206400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100001871","name":"Funda\u00e7\u00e3o para a Ci\u00eancia e Tecnologia","doi-asserted-by":"publisher","award":["Decree-Law 57\/2016","UID\/EMS\/00481\/2019","UIDB\/50011\/2020","UIDP\/50011\/2020"],"award-info":[{"award-number":["Decree-Law 57\/2016","UID\/EMS\/00481\/2019","UIDB\/50011\/2020","UIDP\/50011\/2020"]}],"id":[{"id":"10.13039\/501100001871","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100008530","name":"European Regional Development Fund","doi-asserted-by":"publisher","award":["CENTRO-01-0145-FEDER-022083"],"award-info":[{"award-number":["CENTRO-01-0145-FEDER-022083"]}],"id":[{"id":"10.13039\/501100008530","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001824","name":"Czech Science Foundation","doi-asserted-by":"publisher","award":["Project No. 21-06802S"],"award-info":[{"award-number":["Project No. 21-06802S"]}],"id":[{"id":"10.13039\/501100001824","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001823","name":"M\u0160MT","doi-asserted-by":"publisher","award":["Project SOLID21- CZ.02.1.01\/0.0\/0.0\/16_019\/0000760"],"award-info":[{"award-number":["Project SOLID21- CZ.02.1.01\/0.0\/0.0\/16_019\/0000760"]}],"id":[{"id":"10.13039\/501100001823","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Materials"],"abstract":"<jats:p>Strontium titanate-based materials with ferroelectric or relaxor-like properties have drawn vast attention as polar dielectrics for electronics and telecommunications. Here, we study the lattice dynamics in sol\u2013gel-derived Sr1\u22121.5xBixTiO3 thin films with x = 0.0053 and 0.167, deposited on Al2O3 substrates, using a variable-temperature far-infrared spectroscopy in a transmittance mode. Bi doping, known to induce a low-frequency dielectric relaxation in SrTiO3 (ST) ceramics and films, due to off-centre dopant ion displacements generating electric dipoles, is shown to affect the polar phonon behaviour of thin films. We show that in weakly Bi-doped films, the low-frequency polar TO1 mode softens on cooling but less than in undoped ST. In heavily Bi-doped ST films, this mode displays no significant frequency variation with temperature from 300 to 10 K. The polar phonon behaviour of polycrystalline Bi-doped ST thin films is comparable with that of Bi-doped ST ceramics, which exhibit dielectric relaxations and harden soft-mode behaviour instead of the ferroelectric phase transition.<\/jats:p>","DOI":"10.3390\/ma14216414","type":"journal-article","created":{"date-parts":[[2021,10,26]],"date-time":"2021-10-26T23:54:33Z","timestamp":1635292473000},"page":"6414","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":3,"title":["Polar Phonon Behaviour in Polycrystalline Bi-Doped Strontium Titanate Thin Films"],"prefix":"10.3390","volume":"14","author":[{"ORCID":"https:\/\/orcid.org\/0000-0002-0318-9262","authenticated-orcid":false,"given":"Alexander","family":"Tkach","sequence":"first","affiliation":[{"name":"Department of Materials and Ceramic Engineering, CICECO\u2013Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-0885-7127","authenticated-orcid":false,"given":"Olena","family":"Okhay","sequence":"additional","affiliation":[{"name":"TEMA-Centre for Mechanical Technology and Automation, Department of Mechanical Engineering, University of Aveiro, 3810-193 Aveiro, Portugal"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-7591-8295","authenticated-orcid":false,"given":"Dmitry","family":"Nuzhnyy","sequence":"additional","affiliation":[{"name":"Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Prague, Czech Republic"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-8562-2148","authenticated-orcid":false,"given":"Jan","family":"Petzelt","sequence":"additional","affiliation":[{"name":"Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Prague, Czech Republic"}]},{"given":"Paula M.","family":"Vilarinho","sequence":"additional","affiliation":[{"name":"Department of Materials and Ceramic Engineering, CICECO\u2013Aveiro Institute of Materials, University of Aveiro, 3810-193 Aveiro, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2021,10,26]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1184","DOI":"10.1088\/0370-1298\/63\/10\/118","article-title":"The Dielectric Properties of some Alkaline Earth Titanates at Low Temperatures","volume":"63","author":"Hulm","year":"1950","journal-title":"Proc. Phys. Soc. Sect. A"},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"1176","DOI":"10.1103\/PhysRevLett.19.1176","article-title":"Electric Field Dependence of Optical-Phonon Frequencies","volume":"19","author":"Worlock","year":"1967","journal-title":"Phys. Rev. Lett."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"3593","DOI":"10.1103\/PhysRevB.19.3593","article-title":"SrTiO3: An intrinsic quantum paraelectric below 4 K","volume":"19","author":"Burkard","year":"1979","journal-title":"Phys. Rev. B"},{"key":"ref_4","unstructured":"Tkach, A., and Vilarinho, P.M. (2019). Soft polar phonon mode in SrTiO3 single crystals, ceramics and thin films. Strontium Titanate: Synthesis, Properties and Uses, Nova Science Publishers."},{"key":"ref_5","doi-asserted-by":"crossref","unstructured":"Kleemann, W., Dec, J., Tkach, A., and Vilarinho, P.M. (2020). SrTiO3\u2013glimpses of an inexhaustible source of novel solid state phenomena. Condens. Matter, 5.","DOI":"10.3390\/condmat5040058"},{"key":"ref_6","doi-asserted-by":"crossref","first-page":"104111","DOI":"10.1063\/1.1905789","article-title":"Microwave dielectric properties of single-crystal quantum paraelectrics KTaO3 and SrTiO3 at cryogenic temperatures","volume":"97","author":"Geyer","year":"2005","journal-title":"J. Appl. Phys."},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"5","DOI":"10.1023\/B:JECR.0000015661.81386.e6","article-title":"Ferroelectric Materials for Microwave Tunable Applications","volume":"11","author":"Tagantsev","year":"2003","journal-title":"J. Electroceramics"},{"key":"ref_8","doi-asserted-by":"crossref","first-page":"1624","DOI":"10.1016\/j.sse.2007.09.036","article-title":"High pass filter with above IC integrated SrTiO3 high K MIM capacitors","volume":"51","author":"Wolozan","year":"2007","journal-title":"Solid-State Electron."},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"5501","DOI":"10.1103\/PhysRevB.22.5501","article-title":"Infrared dispersion in SrTiO3 at high temperature","volume":"22","author":"Servoin","year":"1980","journal-title":"Phys. Rev. B"},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"1227","DOI":"10.1103\/PhysRevB.1.1227","article-title":"Anomalous Acoustic Dispersion in Centrosymmetric Crystals with Soft Optic Phonons","volume":"1","author":"Axe","year":"1970","journal-title":"Phys. Rev. B"},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"8046","DOI":"10.1103\/PhysRevB.51.8046","article-title":"Refined treatment of the model of linearly coupled anharmonic oscillators and its application to the temperature dependence of the zone-center soft-mode frequencies of KTaO3 and SrTiO3","volume":"51","author":"Vogt","year":"1995","journal-title":"Phys. Rev. B"},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"858","DOI":"10.1103\/PhysRev.177.858","article-title":"Lattice-Dynamical Study of the 110\u00b0K Phase Transition in SrTiO3","volume":"177","author":"Shirane","year":"1969","journal-title":"Phys. Rev."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"97","DOI":"10.1103\/PhysRev.123.97","article-title":"Nonlinearity and Microwave Losses in Cubic Strontium-Titanate","volume":"123","author":"Rupprecht","year":"1961","journal-title":"Phys. Rev."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"4500","DOI":"10.1103\/PhysRevLett.82.4500","article-title":"Observation of the first-order Raman scattering in SrTiO3 thin films","volume":"82","author":"Sirenko","year":"1999","journal-title":"Phys. Rev. Lett."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"201","DOI":"10.1063\/1.1324457","article-title":"Lattice dynamical properties of SrTiO3 thin films","volume":"535","author":"Sirenko","year":"2000","journal-title":"AIP Conf. Proceed."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"373","DOI":"10.1038\/35006023","article-title":"Soft-mode hardening in SrTiO3 thin films","volume":"404","author":"Sirenko","year":"2000","journal-title":"Nature"},{"key":"ref_17","doi-asserted-by":"crossref","first-page":"885","DOI":"10.1002\/jrs.752","article-title":"Temperature-dependent structural characterization of sol-gel deposited strontium titanate (SrTiO3) thin films using Raman spectroscopy","volume":"32","author":"Gupta","year":"2001","journal-title":"J. Raman Spectrosc."},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"235406","DOI":"10.1103\/PhysRevB.66.235406","article-title":"Origin of soft-mode stiffening and reduced dielectric response in SrTiO3 thin films","volume":"66","author":"Ostapchuk","year":"2002","journal-title":"Phys. Rev. B"},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"297","DOI":"10.1007\/s10832-008-9494-2","article-title":"Polar phonons in some compressively stressed epitaxial and polycrystalline SrTiO3 thin films","volume":"22","author":"Nuzhnyy","year":"2008","journal-title":"J. Electroceramics"},{"key":"ref_20","doi-asserted-by":"crossref","first-page":"613","DOI":"10.1103\/PhysRev.174.613","article-title":"Electric-Field-Induced Raman Scattering in SrTiO3 and KTaO3","volume":"174","author":"Fleury","year":"1968","journal-title":"Phys. Rev."},{"key":"ref_21","unstructured":"Tkach, A., and Vilarinho, P.M. (2019). Effect of bismuth doping on the properties of strontium titanate thin films. Strontium Titanate: Synthesis, Properties and Uses, Nova Science Publishers."},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"151","DOI":"10.1016\/j.jmst.2020.05.064","article-title":"Comment on \u201cHole-pinned defect-dipoles induced colossal permittivity in Bi doped SrTiO3 ceramics with Sr deficiency\u201d","volume":"65","author":"Tkach","year":"2020","journal-title":"J. Mater. Sci. Technol."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"149","DOI":"10.1007\/s12034-018-1677-0","article-title":"Resistance-switching properties of Bi-doped SrTiO3 films for non-volatile memory applications with different device structures","volume":"41","author":"Wang","year":"2018","journal-title":"Bull. Mater. Sci."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"88","DOI":"10.1016\/j.jmat.2018.12.004","article-title":"Influence of Bi on the thermoelectric properties of SrTiO3-\u03b4","volume":"5","author":"Chen","year":"2018","journal-title":"J. Materiomics"},{"key":"ref_25","first-page":"250","article-title":"Relaxation polarization and losses in nonferroelectric dielectrics with high dielectric constants","volume":"6","author":"Skanavi","year":"1958","journal-title":"Sov. Phys. JETP"},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"1487","DOI":"10.1063\/1.1428799","article-title":"Dielectric relaxor and ferroelectric relaxor: Bi-doped paraelectric SrTiO3","volume":"91","author":"Ang","year":"2002","journal-title":"J. Appl. Phys."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"144104","DOI":"10.1103\/PhysRevB.69.144104","article-title":"Broad-band dielectric spectroscopy of SrTiO3:Bi ceramics","volume":"69","author":"Porokhonskyy","year":"2004","journal-title":"Phys. Rev. B"},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"064103","DOI":"10.1063\/1.3549612","article-title":"Dielectric relaxation of Sr1\u20131.5xBixTiO3 sol-gel thin films","volume":"109","author":"Okhay","year":"2011","journal-title":"J. Appl. Phys."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"245","DOI":"10.4028\/www.scientific.net\/MSF.514-516.245","article-title":"Bi Effect on the Microstructure and Dielectric Properties of SrTiO3 Thin Films","volume":"514\u2013516","author":"Okhay","year":"2006","journal-title":"Mater. Sci. Forum"},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"997","DOI":"10.1016\/j.ceramint.2007.09.066","article-title":"Effect of poly(vinyl acetate) on structure and property of bismuth-doped strontium titanate thin films derived by sol\u2013gel method","volume":"34","author":"Zhao","year":"2008","journal-title":"Ceram. Int."},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"084104","DOI":"10.1063\/1.3106162","article-title":"Structure and dielectric properties of (Sr1\u22121.5xBix)TiO3 thin films","volume":"105","author":"Shi","year":"2009","journal-title":"J. Appl. Phys."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"062912","DOI":"10.1063\/1.3463472","article-title":"Dielectric response of polycrystalline Sr1\u22121.5xBixTiO3 thin films under direct current bias","volume":"97","author":"Okhay","year":"2010","journal-title":"Appl. Phys. Lett."},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"10891","DOI":"10.1039\/C9TC03032H","article-title":"Excellent energy storage density and charge-discharge performance in a novel Bi0.2Sr0.7TiO3-BiFeO3 thin film","volume":"7","author":"Song","year":"2019","journal-title":"J. Mater. Chem. C"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"160668","DOI":"10.1016\/j.jallcom.2021.160668","article-title":"Enhancement of energy storage density achieved in Bi-modified SrTiO3 thin films by introducing a TiO2 layer","volume":"882","author":"Liu","year":"2021","journal-title":"J. Alloys Compd."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"413","DOI":"10.1080\/00150199808014890","article-title":"Far-infrared spectroscopy of a SrTiO3 thin film","volume":"208\u2013209","author":"Fedorov","year":"1998","journal-title":"Ferroelectrics"},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"89","DOI":"10.1080\/00150193.2018.1499407","article-title":"Polar phonons in polycrystalline SrTiO3 thin films: The role of the substrate","volume":"532","author":"Okhay","year":"2018","journal-title":"Ferroelectrics"},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"1613","DOI":"10.1016\/S0955-2219(98)00027-2","article-title":"Dielectric relaxation behaviour of Bi: SrTiO3: I. The low temperature permittivity peak","volume":"18","author":"Yu","year":"1998","journal-title":"J. Eur. Ceram. Soc."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"052903","DOI":"10.1063\/1.3549181","article-title":"Enhancement of tetragonality and role of strontium vacancies in heterovalent doped SrTiO3","volume":"98","author":"Tkach","year":"2011","journal-title":"Appl. Phys. Lett."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"184111","DOI":"10.1103\/PhysRevB.64.184111","article-title":"Dielectric, infrared, and Raman response of undoped SrTiO3 ceramics: Evidence of polar grain boundaries","volume":"64","author":"Petzelt","year":"2001","journal-title":"Phys. Rev. B"},{"key":"ref_40","doi-asserted-by":"crossref","first-page":"673","DOI":"10.1103\/PhysRev.59.673","article-title":"On the Polar Vibrations of Alkali Halides","volume":"59","author":"Lyddane","year":"1941","journal-title":"Phys. Rev."}],"container-title":["Materials"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1996-1944\/14\/21\/6414\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,11]],"date-time":"2025-10-11T07:23:56Z","timestamp":1760167436000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1996-1944\/14\/21\/6414"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2021,10,26]]},"references-count":40,"journal-issue":{"issue":"21","published-online":{"date-parts":[[2021,11]]}},"alternative-id":["ma14216414"],"URL":"https:\/\/doi.org\/10.3390\/ma14216414","relation":{},"ISSN":["1996-1944"],"issn-type":[{"type":"electronic","value":"1996-1944"}],"subject":[],"published":{"date-parts":[[2021,10,26]]}}}