Search

Perovskite materials have attracted extensive attention due to their fascinating properties and novel features attributed to the coexistence of ferro/ferri/antiferro-magnetic ground state and semiconductor band gap within the same material. In this research, triple perovskite Sr3Co2WO9 has been successfully synthesized for the first time in the nanocrystalline form with an average crystallite size of 23 nm by means of a modified aqueous citrate sol-gel method. At room temperature, the crystal structure of Sr3Co2WO9 is cubic, space group Fm-3m with lattice parameter a = 7.9073(6) Å. The formation of Sr3Co2WO9 was studied in situ by X-ray diffraction and analysed by the Rietveld analysis. The detected hysteresis loops with non-zero remanent magnetization and rather large coercive field reveal ferrimagnetic ordering with Curie temperature of 144 K. The measured effective magnetic moment of 3B is close to the expected value for rarely observed intermediate spin S = 1. However, this can be also explained as a combination of LS (60 %) and HS (40 %) Co3+. It is found that the compound exhibits the semiconducting properties with the optical band gaps equal to 3.52 eV (indirect) and 3.76 eV (direct), respectively. This was confirmed by AC conductivity measurements, which varies between 10−5 and 10−4 Ω−1 cm−1. The Maxwell -Wagner model is employed to describe the frequency dependent dielectric constant. The frequency dependent AC conductivity follows the universal Jonscher’s power law. Semiconducting properties of this materials could thus be spincontrolled if implemented in devices.

Ceria is a well-known material used as catalyst for different oxidation reactions due to the presence of oxygen vacancies owing to switchable oxidation states. However, the stability of ceria is low at elevated temperatures which is why it is doped with zirconia as a catalyst support. In this research CexZr1−xO2 solid solutions and dry impregnated and calcined CeO2 on ZrO2 particles were prepared in order to explore catalytic activity for the CO oxidation. The as-prepared compounds were characterized by the X-ray diffraction (XRD) followed by the Rietveld refinement, Raman spectroscopy (Raman), and X- ray photoelectron spectroscopy (XPS). The distinct morphology of CeO2 on ZrO2 particles is responsible for the high specific activity in the gas-phase oxidation. The complete oxygen storage capacity (OSCc) at 430 °C is shown to be linearly correlated to the CO oxidation activity at 430 °C as a function of the Ce concentration x. Thus, it is compatible with the expected Mars–van-Krevelen mechanism. The CeO2 on ZrO2 catalyst calcined at 600 °C is chemically even more stable than the one calcined at 900 °C, where a solid solution of ZrO2 and CeO2 is formed at the solid interface. The improved stability of the CeO2 layer calcined at 600 °C is traced to its sharp interface formed with the ZrO2 support. This kind of active and stable layer morphology of CeO2 supported on ZrO2 could be beneficial for other catalytic oxidation reactions as well.

Polar perovskite materials have attracted extensive attention due to the coexistence of magnetic ground state and semiconductor band gap within the same material. For the first time triple perovskite Sr3Co2WO9 has been synthesized in the nanocrystalline form with an average crystallite size of 23 nm using a modified aqueous citrate sol-gel method. The crystal structure of Sr3Co2WO9 is cubic at the room temperature, space group Fm-3m with with lattice parameter a= 7.9073(6) Å. The formation of Sr3Co2WO9 was studied by cyclic voltammetry, UV/Vis spectroscopy and in situ X-ray diffraction method subsequently analysed by the Rietveld analysis. The detected hysteresis loops reveal ferrimagnetic ordering with Curie temperature of 144 K. The measured effective magnetic moment of 3 _B is close to the expected value for rarely observed intermediate spin S = 1 but can also be explained as a combination of HS (40 %) Co3+ and LS (60 %). The compound exhibits the semiconducting properties with the optical band gaps equal to 3.52 eV (indirect) and 3.76 eV (direct), respectively, calculated from UV/Vis absorption spectrum using the Tauc method. Semiconducting nature was also confirmed by AC conductivity measurements, which is between 10−5 and 10−4 Ω−1 cm−1. The frequency dependent dielectric constant was explained by employing the Maxwell-Wagner model. The frequency dependent AC conductivity follows the universal Jonscher’s power law. This material could be a good candidate for implementation as a constituent for devices where its semiconducting properties would be spin controlled.

The properties of materials have appeared to be size- and shape-dependent which is why in this work we compare two synthesis routes: sol-gel solution synthesis and solid state synthesis of triple Sr3Fe2WO9 perovskite. This material has been prepared in form of semi- spherical particle agglomerates using a modified aqueous sol–gel citrate route and as a bulk material using solid state synthesis by means of planetary ball milling. Structural investigation has been conducted by ambient and in situ X-ray powder diffraction (XPRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA) and unpolarized Raman spectroscopy. Results of powder X-ray diffraction show phase pure nanocrystalline Sr3Fe2WO9 prepared by sol-gel route, while compounds prepared by solid state method contained larger amount of impurities. It has been revealed that synthesized compound crystalizes in tetragonal system (space group I4/m) with crystallite size of 36 nm and high crystallinity. Magnetic properties have been determined using SQUID measurements and have shown ferrimagnetic ordering with gradual transition around Curie temperature of 213 K as opposed to bulk Sr3Fe2WO9 with sharp transition at 373 K. Optical properties have been estimated using Tauc method which revealed band gap values of 2.71 еV for direct band gap and 2.10 eV for indirect band gap. Authors acknowledge Croatian Science Foundation (IP- 2016-06-3115) for full financial support.

CeO2 ist ein vielversprechendes Material für die katalytische Rückgewinnung von Chlor aus der heterogen katalysierten Umsetzung von Chlorwasserstoff und Sauerstoff (Deacon-Prozess). Sowohl die hohe thermische Stabilität als auch die Fähigkeit Sauerstoff leicht ein- und auszubauen, ermöglichten CeO2 sich in den letzten Jahren als potenzielle Alternative für den momentan eingesetzten und kostenintensiven RuO2-Katalysator zu etablieren. Um den Einfluss der Sauerstoffspeicherkapazität (engl. oxygen storage capacity, kurz: OSC) von CeO2 mit den katalytischen Eigenschaften im Deacon-Prozess aufzuklären, wurden CeO2-basierte Mesostrukturen hergestellt, welche einerseits über eine hohe spezifische Oberfläche und andererseits über eine hohe Zugänglichkeit für gasförmige Reaktanden verfügen.Auf Basis der Sol-Gel-Synthese und dem eingesetzten Templat Poly(isobuten)-block-Poly(ethylenoxid) (PIB-b-PEO) wurden mesoporöse CeO2-Materialien hergestellt, die über eine kubische Porenstruktur mit Mesoporendurchmessern von ca. 12-14 nm verfügen. Eine anschließende Dotierung von alio-/isovalenten Metallionen (Gd3+, Zr4+, Pr3+/4+, Tb3+/4) zeigte, dass keine direkte Korrelation zwischen der OSC und der katalytischen Aktivität im Deacon-Prozess besteht. Anders als die Aktivität, kann die beobachtete mangelnde katalytische Stabilität der auch nur teilweise aliovalent-dotierten CeO2-Mesostrukturen über die zu hohe Anzahl von Sauerstoffstellen erklärt werden, die die Formation von inaktivem CeCl3 fördern. Im Vergleich dazu erwiesen sich die Zr-dotierten CeO2-Strukturen aufgrund ihrer hohen katalytischen Stabilität als vielversprechend. Das zuvor entwickelte Synthesekonzept wurde erweitert, um neben molekularen Präkursoren auch vorgefertigte Nanopartikel für den Templatierungsprozess zu verwenden. So konnte in einem zweiten Projekt der Einfluss der Mesostrukturierung auf die OSC und die katalytischen Eigenschaften in der HCl-Oxidation untersucht werden. Anders als die identisch behandelten aber nicht mesostrukturierten Nanopartikel, ermöglicht die kontrollierte Anordnung solcher Nanopartikel rundum sphärischer Mesoporen einen besseren Zugang zur aktiven Oberfläche, was durch die erhöhte dynamische Sauerstoffspeicherkapazität und spezifische Produktbildungsrate in der HCl-Oxidation (engl. space time yield, kurz: STY) verifiziert wurde.Des Weiteren wurde mesoporöse Metalloxid-Dünnfilme für die Deposition von definierten CeO2-Schichten in mesoporösen ZrO2-Substraten mithilfe der Atomlagenabscheidung (engl. atomic layer deposition, kurz: ALD) verwendet, um in zukünftigen Projekten die Abhängigkeit der OSC von der CeO2-Schichtdicke unter realen Bedingungen zu studieren. Obwohl die mesoporösen Dünnschichten ideale Modellsysteme sind, um den Wachstumsprozess mittels ALD zu verfolgen, verfügen sie nicht über eine ausreichend hohe absolute Oberfläche um die OSC im Flussreaktor zu vermessen. Da die OSC ähnlich wie die ionische und elektronische Leitfähigkeit von der Anzahl der Sauerstoffleerstellen und deren Mobilität bei gegebener Temperatur abhängt, wurde die Gesamtleitfähigkeit der CeO2/ZrO2-ALD-Schichten mithilfe der Impedanzspektroskopie untersucht. Hiermit konnte demonstriert werden, dass ein Leitfähigkeitsmaximum bei einer Schichtdicke von 3,4 nm vorliegt, welches sehr gut mit theoretischen Berechnungen zum energetischen Minimum der Sauerstoffvakanzbildungsenthalpien in der Literatur übereinstimmt.Das vorgelegte Promotionsprojekt demonstriert, dass sich mesoporöse CeO2-Katalysatoren dank ihrer hohen spezifischen Oberfläche und guten Zugänglichkeit für gasförmige Reaktanden ideal als Modellsysteme sowohl für die katalytischen Untersuchungen in der HCl-Oxidation als auch für conformality-Studien zur Abscheidung von Metalloxiden mittels ALD eignen. Zukünftige Studien sollten bevorzugt mesoporöse CeO2-Materialien als Modellkatalysatoren einsetzen, um den Einfluss der OSC nicht nur auf die HCl-Oxidation, sondern auch auf andere Oxidationsreaktionen aufzuklären. Dabei ist die hier beschriebene Herstellung innovativer MOx-CeO2 Kern-Schale-Modellsysteme durch die ALD zukunftsweisend, um nicht nur das Verständnis der OSC und der katalytischen Eigenschaften zu vertiefen, sondern auch um neuartige Metalloxidkatalysatoren mit hoher gemeinsamer Grenzfläche zu entwickeln.

Oxygen storage in solid catalyst is very important for heteregeneous oxidation reactions of environmentally harmful gases such as CO, CHx and HCl. Ceria nanoparticles act as promising catalysts these kind of reactions because it possesses high OSC (oxgen storage capacity). When reducing size of a material, surface becomes more important than a bulk. Also, surface defects are induced which favor high OSC. This is why in these kinds of reactions the interaction of a gas phase with solid surface is studied in detail. Redox reactions which occur on ceria surface usually follow Mars-van Krevelen mechanism (surface oxygen atoms directly involved in reactions). Neutral oxygen vacancies are formed because of the reversible change in oxidation state from Ce4+ to Ce3+. These vacancies are formed in different quantities depending on a shape of synthesized nanomaterial. Different shapes show different facets of preferential orientation ((110) for nanorods and (100) for nanocubes) thus also showing different stability and activity. In this research, shape-controlled CeO2 nanoparticles (nanorods and nanocubes) and Zr-doped ceria nanorods were synthesized by hydrothermal method. Synthesized materials have been characterized by powder X-ray diffraction (PXRD), Raman spectroscopy, scanning electron microscopy (SEM) and thermogravimetric analysis (TGA). The value of surface area has been measured by BET method. Obtained results show pronounced effect of different nanoshape of ceria on formation of oxygen vacancies. The authors acknowledge Croatian Science Foundation-Unity through knowledge fund project PZS-2019-02-2467 for full financial support.

Specific structure of perovskite compounds provides them with various interesting properties which vary from magnetic and electric properties to magnetic frustration and half‐metallicity. Because of their properties they can be found in numerous technological applications such as transducers, memory devices, solar cells, etc. A3B2(W/Te)O9 (A=Sr, Ba ; B=Fe, Co) triple perovskites have been prepared in nanocrystalline form using a modified sol‐gel route with citric acid as a chelating agent. These materials have been studied by X‐ray powder diffraction (PXRD), X‐ ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and unpolarized Raman spectroscopy, while their magnetic properties have been determined using SQUID measurements. Similar research has already been done with tellurium‐ and tungsten‐ based perovskites. In this research the advances of solution chemistry methods (bottom up approach), namely sol‐gel citrate route, over the solid state routes towards the synthesis of complex perovskite structures will be presented.

Razvojem sinteze bez otapala trostrukog perovskita (Ca3Fe2MO9 gdje je M = W, Te, Mo) podrazumijeva pronalazak optimalnih uvjeti u kojima bi se dobio fazno čisti produkt. Parametri koji su mijenjani tijekom eksperimenata bili su brzina i vrijeme: 3 različite brzine vrtnje (250, 500 i 750 ok/min) i vrijeme sinteze svakih 10 min u razmaku od 10 do 120 minuta. Budući da se pokazalo da je pri najmanjoj brzini okretanja (250 ok/min) i najkraćem vremenu sinteze (10 min) najveća fazna čistoća produkta, dodatno su ispitivani utjecaji promjene brzine okretaja (100, 150, 200 i 250 ok/min) pri vremenu 10 minuta. Sintetizirani uzorci su analizirani termogravimetrijski (TGA), infracrvenom spektroskopijom (FT-IR) i rentgenskom difrakcijom na prahu (PXRD). Perovskiti su spojevi koji zbog svoje specifične strukture mogu pokazivati feroelektrična i feromagnetična svojstva te zbog toga mogu imati primjenu u različitim tehnološkim uređajima (memorijski uređaji, solarne ćelije itd.). U ovom slučaju Zbog toga je važno razviti ekološki prihvatljivu i ekonomičnu metodu sinteze ovakvih spojeva, kao što je sinteza bez otapala (eng. Solvent-free synthesis) korištena tijekom ovih istraživanja. Ovo je istraživanje financirano u potpunosti od strane Hrvatske zaklade za znanost "Istraživanje složenih multiferoičnih materijala pripravljenih metodama otopinske kemije" i djelomično od strane HAZU "Istraživanje složenih metalnih oksida na osnovi molibdena".

Sinteza bez otapala (eng. Solvent-free) trostrukog perovskita (Ca3Fe2WO9) je metoda u kojoj se koristi amonijev hidrogenkabonat uz miješanje s nitratima metalnih soli u reakcijskoj posudi planetarnog kugličnog mlina. Amonijev hidrogenkarbonat se raspada na amonijak i vodu pri 36 °C pri čemu stvara lužnati medij za katione metala koji će tvoriti hidrokside. Perovskiti su spojevi opće formule ABO3 (A- kation većeg ionskog promjera, B- kation manjeg ionskog promjera, O-kisik). Kristali perovskita zbog svoje specifične strukture mogu pokazivati feroelektrična i feromagnetična svojstva te zbog toga mogu imati primjenu u različitim tehnološkim uređajima (memorijski uređaji, solarne ćelije itd.). Sintetizirani uzorci su analizirani infracrvenom spektroskopijom (FT-IR), termogravimetrijskom analizom (TGA) te rendgenskom difrakcijom na prahu (PXRD). Cilj ovog istraživanja je pronaći optimalne uvjete za sintezu fazno čistog produkta koji će se dalje detaljno strukturno karakterizirati te će mu se odrediti svojstva. Ovaj je rad dio projekta Hrvatske zaklade za znanost (HRZZ-IP- 2016-06-3115)

Specific structure of perovskite compounds provides them with various interesting magnetic, dielectric and optical properties. It has become very trendy to alter particle size instead of altering chemical composition since the properties of materials have appeared to be size- and shape-dependent. Triple Sr3Fe2WO9 perovskite has been prepared in form of semi- spherical particle agglomerates using a modified aqueous sol–gel citrate route. Synthesis mechanism and redox properties of precursor metal salts in aqueous solution have been studied by electrochemical measurements and UV/VIS absorbance spectros-copy where it has been observed that Fe3+ is stable after coordination with ammonia molecules . Structural investigation has been conducted by ambient and in situ X-ray powder diffraction (XPRD), X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FTIR) and unpolarized Raman spectroscopy and it has been observed that synthesized compound crystalizes in tetragonal system (space group I4/m) with crystallite size of 36 nm and high crystallinity and fully transforms into desired perovskite compound at 1273 К. Magnetic properties have been determined using SQUID measurements and have shown ferrimagnetic ordering at 373 K. Dielectric properties have revealed a proportional increase of dielectric constant with temperature and reverse proportional decrease with frequency. Optical properties have been estimated using Tauc method which revealed band gap values of 2.71 еV for direct band gap and 2.10 eV for indirect band gap. Authors acknowledge Croatian Science Foundation (IP-2016-06-3115) for full financial support.

U ovom radu ispitivani su optimalni parametri pri hidrotermalnoj sintezi s ciljem dobivanja trostrukog perovskita, Sr3Mn2MoO9, iz prekursora metalnih soli (Sr(NO3)2, Mn(NO3)2 • 4H2O, (NH4)6Mo7O24 • 4H2O) otopljenih u vodi. Ovakav trostruki perovskit bi teorijski bio izostrukturan s Sr3Fe2MoO9 zbog identičnog kationskog radijusa visokospinskih Fe3+ i Mn3+ (0.645 Å), ukoliko bi u ovom spoju ovi kationi bili visokospinski. Klasičan način dobivanja perovskita zahtijeva kontrolirano, dugotrajno i umjereno žarenje što se upravo ovim radom želi izbjeći, koristeći blaže uvjete (relativno niska temperatura, 150 ºC i 200 ºC) i kraće vrijeme sinteze (24h), uz manje troškove i ekološku prihvatljivost. Neprestani razvoj donosi novije i naprednije materijale koji sve više postaju nanometarskoga reda veličine. Upravo zbog toga provedena su elektrokemijska mjerenja kako bi se ispitala oksidacijska stanja metalnih kationa u početnoj otopini pri zadanim reakcijskim uvjetima i prisustvu jake lužine (natrijeva hidroksida). Cilj samoga rada je pronaći optimalne parametre za sintezu sustava koji sadrži tri kationske vrste (stroncij, mangan, molibden) ispitati sastav, morfologiju i stabilnost dobivenih produkata rentgenskom difrakcijom na prahu (PXRD), infracrvenom spektroskopijom (FTIR), UV/VIS spektroskopijom te termogravimetrijskom analizom (TGA). Ovaj rad je izrađen na Odjelu za kemiju Sveučilišta J.J. Strossmayera u Osijeku pod mentorstvom izv. prof. Igora Đerđa, a kao dio projekta Hrvatske zaklade za znanost – HRZZ (IP-2016-06-3115) i parcijalno kao dio projekta HAZU „Istraživanje složenih metalnih oksida na osnovi molibdena“.

Perovskiti su spojevi kristalne strukture opće formule ABO3 (A = kation većeg ionskog promjera, B = kation manjeg ionskog promjera, O = kisik). Njihova upotreba u modernom životu je široko rasprostranjena, najviše u digitalnom svijetu gdje se teži ka umanjenju elektroničkih uređaja i povećanju gustoće zapisa podataka. Sol-gel kemija opisuje preobrazbu tekućih prekursora u sol, te na kraju u gel. Metode su vrlo osjetljive jer se mogu dobiti različite strukture iz istih prekusrora s malim promjenama reakcijskih uvjeta. U radu je prikazana citratna sol-gel sinteza složenih metalnih oksida perovskitne strukture pri čemu je za kation na A položaju korišten stroncijev kation, a za kation na jednom B položaju kobaltov kation. Osušeni uzorci su kalcinirani u peći u dva koraka, pri 600 ˚C i 950 ili 1000 ˚C. Za istraživanje sintetskog mehanizma i dobivenih produkata korištene su sljedeće metode: FTIR spektroskopija, terrmogravimetrijska analiza (TGA), elektrokemijska mjerenja (ciklička voltametrija), rentgenska difrakcija na prahu pri sobnoj temperaturi (PXRD), in situ rentgenska difrakcija na prahu do 900 ˚C, UV/VIS spektroskopija. Ovim su rezultatima prikazane mogućnosti sinteze trostrukih perovskita teorijski sličnih struktura u kojima se jedino izmjenjuju magnetski neaktivni kationi sličnih ionskih radijusa W6+ (0.60 Å), Te6+ (0.56 Å) i Mo6+ (0.59 Å). Ovaj rad je izrađen na Odjelu za kemiju Sveučilišta J.J. Strossmayera u Osijeku pod mentorstvom izv. prof. Igora Đerđa, a kao dio projekta Hrvatske zaklade za znanost – HRZZ (IP-2016-06-3115) i parcijalno kao dio projekta HAZU „Istraživanje složenih metalnih oksida na osnovi molibdena“.

Specific structure of perovskite compounds provides them with various interesting properties which vary from magnetic and electric properties to magnetic frustration and half-metallicity. Since it is hard to stabilize Mn3+ cation in solid form, it is important to use solution chemistry methods. Sr3Mn2(W/Te)O9 triple perovskites have been prepared by means of hydrothermal method with sodium hydroxide as mineralizer and ethanol as buffering agent. Since the high spin 6-coordinated Mn3+ cation and Fe3+ cation have the same values of ionic radius (0.645 Å), it is reasonable to expect similar structure of Sr3Mn2(W/Te)O9 and corresponding Sr3Fe2(W/Te)O9 compounds [1, 2]. It is important to find suitable synthesis route for stabilization of desired oxidation state of transition metal cation. Stabilization of cations in solution and synthesized compounds itself have been investigated by electrochemical measurements. Structural characterization has been done by X-ray powder diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA) and unpolarized Raman spectroscopy, while their magnetic properties have been determined using SQUID measurements. Similar research has already been done with tellurium- and tungsten- based perovskites. In this research the advances of solution chemistry methods (bottom up approach), over the solid state routes towards the synthesis of complex perovskite structures will be presented.

Perovskites are the compounds with a general formula ABO3 (A = larger cation, B = smaller cation, O = oxygen). The ideal perovskites crystallize in a cubic crystal system that can be predicted by the Goldschmidt tolerance factor formula. Their usage in modern life is widespread, mostly in the digital world, where the emphasis is on the size reduction of the electronic devices and on an expanding density of data storage. The sol‐gel chemistry describes a transformation of a liquid precursor into a sol and finally into a gel. These methods are very sensitive because different structures may be obtained using the same precursors, with small modifications in the reaction conditions. This study presents a citrate sol-gel route of complex metal oxides with a perovskite crystal structure type previously reported in similar compounds. The dried samples were calcined in two steps, at 600 ˚C and 950 or 1000 ˚C. The synthesized samples were investigated by the powder X‐Ray diffraction to determine a phase composition, FT‐IR spectroscopy to determine the presence of organic impurities, and by a thermogravimetric analysis coupled with a differential scanning calorimetry (TGA/DSC) to analyze a thermal stability of the compound and possible phase transitions. The electrochemical measurements were conducted in order to determine an oxidation state of transition metals in the reaction mixture and to determine the reaction mechanism. The in‐situ X-ray diffraction measurements were conducted up to 900 ˚C to identify the structural changes during calcination. The results revealed the successfully synthesized tellurium‐based metal oxides with a double (A2Ni(Te/W)O6, A = Sr, Ba) and triple (A3Co2TeO9, A = Sr, Ba) perovskite structure type. This research is a part of the Croatian Science Foundation project entitled Investigation of Complex Multiferroic Materials Prepared by the Solution Chemistry Methods under the supervision of Prof. Igor Đerđ, Ph.D.

Specific structure of perovskite compounds provides them with various interesting properties which vary from magnetic and electric properties to magnetic frustration and half-metallicity. Double A2Ni(Te, W)O6 and triple A3(Fe, Co)2(W/Te)O9 (A=Sr, Ba) perovskites have been prepared in nanocrystalline form using a modified aqueous sol–gel citrate route. Solution chemistry synthesis mechanism and synthesized compounds itself have been studied by electrochemical measurements. Structural investigation has been conducted by ambient and in situ X-ray powder diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), selected area electron diffraction (SAED), thermogravimetric analysis (TGA) and unpolarized Raman spectroscopy, while their magnetic properties have been determined using SQUID measurements. Similar research has already been done with tellurium- and tungsten- based perovskites. In this research the advances of solution chemistry methods (bottom up approach), namely sol-gel citrate route, over the solid-state routes towards the synthesis of complex perovskite structures will be presented.

Perovskite materials exhibit interesting physical properties due to their exceptional structure. Those properties have been studied for various practical applications: from superconductors, electrode and electrolyte materials for fuel cells, catalytic converters in diesel vehicles, components for solar cells to the memory device components. While numerous metal oxide combinations with single, double and triple perovskite structure have been characterized so far, only few of them have been synthesized in nanocrystalline form. Since nanosized materials have exceptional properties due to the quantum size effect, nanocrystalline perovskites could possess interesting properties. Hereby we present nanocrystalline A3B2(W/Te)O9 and A2B(W/Te)O6 (A=Sr, Ba, Ca ; B=Fe, Co, Mn, Ni) with double and triple perovskite structure that have been synthesized using bottom up approach in liquid state. We investigated reaction mechanisms of synthetic routes, structurally characterizied synthesized compounds and measured their properties in comparison with corresponding bulk materials.

This study presents an optimization of hydrothermal synthesis of triple perovskites Sr3Mn2WO9 and Sr3Mn2TeO9, from an aqueous solution of metal salt precursors. Usually, a synthesis of perovskite materials demands a controlled and long‐term annealing. In this research, milder conditions (a relatively low temperature, 150 ºC and 200 ºC) and shorter reaction time (24 h) were created, which are environmentally friendly and low-cost. A continuous development contributes to the new and more advanced nanosized materials. It is important for a design of perovskite materials to stabilize the metal cations in certain oxidation states. For that purpose, electrochemical measurements were carried out to determine an oxidation state of manganese cation in the given reaction conditions. The electrochemical results indicate that manganese is in the +3 oxidation state while being transformed into a desired compound. This oxidation state is stabilized by the usage of a strong base (sodium hydroxide). An interesting fact is that Mn3+ (coordination number 6, a high spin state) has an ionic radius of 0.645 Å, which corresponds to the ionic radius of Fe3+ (also coordination number 6, a high spin state). Hence, a structural similarity to Sr3Fe2WO9 and Sr3Fe2TeO9, is expected. In conclusion, the composition, morphology, and stability of prepared compounds were investigated by means of the powder X‐ray diffraction (PXRD), Fourier‐transform infrared spectroscopy (FT-IR), thermogravimetric analysis coupled with the differential scanning calorimetry (TGA/DSC) and the X‐ray photoelectron spectroscopy (XPS). This research is a part of the Croatian Science Foundation project entitled Investigation of Complex Multiferroic Materials Prepared by the Solution Chemistry Methods under the supervision of Prof. Igor Đerđ, Ph.D.