We have found that single-crystal substrates of ZrO2(Y2O3) with (001) and (111) orientation are suitable for the growth of (110) perovskite films of La0.7Ca0.3MnO3, La0.7Sr0.3MnO3 and La1−xMnO3 (x=0.1–0.25) with the in-plane variant structure. The orientation types and crystallographic domains were determined by X-ray diffraction and high-resolution TEM. Special high-angle boundaries formed between the nanodomains of the epitaxial variants result in the high tunnel magnetoresistance (above 15% at 77K and 0.1T). The magnetic reversal transition was also detected in the field below 0.01T, the sharpness of the transition was found to be very sensitive to the film microstructure. Further enhancement of the magnetoresistance was achieved in the heterostructures including perovskite manganite and ferrimagnetic insulating oxide layers.

The formation of previously unknown hexagonal modifications of orthoferrites RFeO3 (R = Eu-Lu) was observed on ZrO2(Y2O3) (111) substrates at 900 degreesC. XRD and HREM studies reveal epitaxial growth of the hexagonal film. The structure of the hexagonal RFeO3 was assigned to the ferroelectric space group P6(3)cm. The typical structural defects in the hexagonal RMnO3 films on ZrO2(Y2O3) (111) are described. Parallel deposition on perovskite substrates results in the stable perovskite phase. The epitaxial stabilization concept successfully explains the experimental results.

The formation of the high-temperature hexagonal modification of DyMnO3 and nonexisting as bulk hexagonal EuMnO3, GdMnO3, and SmMnO3 was observed on ZrO2(Y2O3) (111) substrates at 900 °C due to epitaxial stabilization. HREM study reveals epitaxial growth of the hexagonal film of limited thickness depending on the nature of the rare earth cation. For thickness exceeding critical, the oriented stable perovskite form grows semicoherently on the hexagonal phase. The interface of two polymorphs is not abrupt and involves the formation of the transition zone with the characteristic pyramid-like shapes on the top of the hexagonal layer. The typical structural defects in the hexagonal RMnO3 films are described.

Zeitschrift für anorganische und allgemeine ChemieVolume 628, Issue 9-10 p. 2186-2186 Poster Synthesis and Investigation of Alkaline-doped Manganites — New Magnetoresitive Materials A. Yu. Ganinea, Corresponding Author A. Yu. Ganinea Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 StuttgartMax-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 StuttgartSearch for more papers by this authorO. Yu. Gorbenko, O. Yu. Gorbenko Chemistry Department, Moscow State University, 119899 Moscow, RussiaSearch for more papers by this authorI.E. Graboy, I.E. Graboy Chemistry Department, Moscow State University, 119899 Moscow, RussiaSearch for more papers by this authorA. R. Kaul, A. R. Kaul Chemistry Department, Moscow State University, 119899 Moscow, RussiaSearch for more papers by this author A. Yu. Ganinea, Corresponding Author A. Yu. Ganinea Max-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 StuttgartMax-Planck-Institut für Festkörperforschung, Heisenbergstr. 1, D-70569 StuttgartSearch for more papers by this authorO. Yu. Gorbenko, O. Yu. Gorbenko Chemistry Department, Moscow State University, 119899 Moscow, RussiaSearch for more papers by this authorI.E. Graboy, I.E. Graboy Chemistry Department, Moscow State University, 119899 Moscow, RussiaSearch for more papers by this authorA. R. Kaul, A. R. Kaul Chemistry Department, Moscow State University, 119899 Moscow, RussiaSearch for more papers by this author First published: 01 October 2002 https://doi.org/10.1002/1521-3749(200209)628:9/10<2186::AID-ZAAC11112186>3.0.CO;2-BAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume628, Issue9-10September 2002Pages 2186-2186 RelatedInformation

The results of the simultaneous deposition of Mn3O4 films 100 nm thick at 750 °C and P(O2)=1 mbar by MOCVD on three different single crystal substrates (MgO, LaAlO3 and SrTiO3) are considered. Using X-ray diffraction, Raman spectrometry, high-resolution transmission electron microscopy and magnetic measurements we have demonstrated that the films grown on MgO differ greatly from the stable tetragonal bulk form of Mn3O4 (hausmannite) and are very similar to the high-temperature cubic form with the suppressed Jahn–Teller distortion in manganese–oxygen octahedra. The hausmannite films of the mixed orientations were grown on perovskite substrates. The experimental results are discussed in the framework of the epitaxial stabilization model.

For Abstract see ChemInform Abstract in Full Text.

The epitaxial films of perovskite manganites (La1−xPrx)0.7Ca0.3MnO3 (x=0–1) and nickelates RNiO3 (R=Pr, Nd, Sm, Gd) were grown by single source MOCVD on perovskite substrates producing anisotropic lattice strain in the film. We applied the data on the metal–insulator transition in the perovskite films as a probe for the microscopic strain mechanism. As a result, the anisotropic tilting of the rigid octahedra was deduced for the manganites and octahedra deformation for the nickelates.

The approach to the growth of stoichiometric lead-containing complex oxide films was developed. It was successfully used for the MOCVD of La1-xPbxMnO3 (x = 0.1-0.6) and PbTiO3 films on perovskite substrates and MgO at a deposition rate of approximate to1 mum/h. The grown films were of a good epitaxial duality with rather low mean surface roughness, S-a < 2 nm (for the film thickness 250-600 nm). The grown manganite layers were metallic at room temperature with a T-c above 300 K. Such films are suitable for the fabrication of low-field tunnel magnetoresistance devices and thin film capacitors.

Thin films of rare-earth nickelates RNiO3 (R=Pr, Nd, Sm, Gd) were prepared under a reduced oxygen pressure of <0.02 bar by MOCVD on perovskite substrates. The film–substrate lattice mismatch is critical for the epitaxial stabilization of RNiO3. Increase of the lattice mismatch or film thickness results in the deposition of rare-earth oxides and NiO instead of RNiO3. The transport properties of the films on LaAlO3 were similar to those of the bulk material of the same composition under an applied pressure of 9 kbar. The properties of RNiO3 films with a sharp metal-to-insulator transition can be effectively tuned by the lattice strain.

Colossal negative magnetoresistance is found over a wide range of temperatures below the Curie point T-C approximate to 240 K in an epitaxial La-0.35 Nd0.35Sr0.3MnO3 film on a single-crystal (001)ZrO2(Y2O3) wafer substrate. Isotherms of the magnetoresistance of this film reveal that its absolute value increases with the field, abruptly in the technical magnetization range and almost linearly in stronger fields. For three epitaxial films of the same composition on (001)LaAlO3, (001)SrTiO3, and (001)MgO substrates, colossal magnetoresistance only occurred near T-C approximate to 240 K and at T < T-C it increased weakly, almost linearly with the field. In the film on ZrO2(Y2O3) substrate the electrical resistivity was almost 1.5 orders of magnitude higher than that in the other three films. It is shown that this increase is attributable to the electrical resistance of the interfaces between microregions having four types of crystallographic orientation, while the magnetoresistance in the region before technical saturation of the magnetization is attributable to tunnelling of polarized carriers across these interfaces which coincide with the domain walls tin the other three films there is one type of crystallographic orientation). The reduced magnetic moment observed for all four samples, which is only 46% of the pure spin value, can be attributed to the existence of magnetically disordered microregions which originate from the large thickness of the domain walls which is greater than the size of the crystallographic microregions and is of the same order as the film thickness. The colossal magnetoresistance near T-C and the low-temperature magnetoresistance in fields exceeding the technical saturation level can be attributed to the existence of strong s-d exchange which is responsible for a steep drop in the mobility of the carriers (holes) and their partial localization at levels near the top of the valence band. Under the action of the magnetic field the carrier mobility increases and they become delocalized from these levels.

3d-metal perovskites are promising thin film materials with a great variety of electrical and magnetic properties. We have deposited the epitaxial heterostructures including different combinations of CMR manganites (La 1-x Pr x ) 0.7 Ca 0.3 MnO 3 , (x=0-1), metallic nickelates RNiO 3 (R = Pr, Nd, Sm) with sharp metal-insulator transition and antiferromagnetic insulators RFeO 3 (R = Nd, Eu). The heterostructures were characterised by XRD, SEM, EDX, HREM, RBS, electric and magnetic measurements. Particular attention is paid to the lattice strain in the layers and the structure of their interfaces. The prototype electronic devices based on the heterostructures are discussed.

A self-tuning approach to the growth of lead-containing complex oxide films free of secondary phases was developed. Due to the volatility of lead oxide one can establish the process conditions when the phase purity is provided in spite of any fluctuations of the mass fluxes. An additional advantage is suppression of the surface roughening with the increase of the film thickness providing high smoothness (S a = 1.2-1.5 nm) at the deposition rate up to ∼1μm/h. The effect is due to the quasi-liquid PbO-based surface layer activating the surface diffusion during the film growth. This approach was successfully used for the growth of single phase epitaxial CMR La 1-x Pb x MnO 3 (x=0. 1-0.6), ferroelectric PbTiO 3 films, scintillator material PbWO 4 and the multilayers which were characterised by XRD, SEM, EDX, RBS, HREM, AFM, electric and magnetic measurements.

Using injection, powder-flash and band-flash MOCVD techniques, epitaxial thin films of Nd, Ho, Y, Tm, Dy and Lu manganites were prepared. The formation of high-pressure phase NdMn7O12 as a thin surface layer on Pnma Nd1−xMnO3+δ (x∼0.15) in an Nd-deficient system and HoMnO3, YMnO3, TmMnO3 and LuMnO3 as perovskite phases (known in the bulk only as high-pressure phases) on a LaAlO3 substrate were observed. The remarkable reduction in the pressure needed for formation of the phases in epitaxial films in comparison with bulk samples is a manifestation of the epitaxial stabilisation discussed in the paper. The details of the crystal and domain structure of the films as observed by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution electron microscopy (HREM) techniques are described.

This paper is a survey of recent author’s results obtained by the authors. It shows that many oxides can be obtained as thin epitaxial films in spite of their thermodynamic instability in bulk state at the film deposition conditions. This new synthetic approach, named epitaxial stabilization, is based on free energy gain due to structural coherence at the film/substrate interface. The epitaxial stabilization can be effectively used to enlarge the spectrum of new functional materials.

Thin films of the perovskite manganites solid solutions, including (La,R)1−xAxMnO3 (R=Pr, Nd, A=Ca,Sr,Na) on the single crystalline substrates (LaAlO3, SrTiO3, ZrO2(Y2O3), MgO) were characterized by X-ray diffraction and HREM. Some compounds (like (La1−xPrx)0.7Ca0.3MnO3) have an orthorhombic structure while others (like La1−xNaxMnO3 and La0.7Sr0.3MnO3) are rhombohedral. A strong tetragonal lattice strain owing to the film-substrate lattice mismatch was found in particular in very thin films. In the thicker films this strain was more persistent for compositions the bulk of which is orthorhombic. By HREM, twinning due to the cubic to orthorhombic phase transition was found for (La1−xPrx)0.7Ca0.3MnO3 films, whereas XRD gave the mean tetragonal ratio of the lattice parameters. Misfit dislocations with various Burger vectors occur in the manganites films on LaAlO3 and SrTiO3. An example of the growth of the epitaxial heterostructures with CMR manganites and high Tc superconductors is given.

We have succeeded in the preparation of thin films of rare-earth nickelates RNiO3 (R=Pr, Nd, Sm, and Gd) under reduced oxygen pressure <0.02 bar by metalorganic chemical-vapor deposition owing to their epitaxial stabilization on perovskite substrates. The film–substrate lattice mismatch is critical for the epitaxial stabilization of RNiO3 phases. Increase of the lattice mismatch or film thickness results in the deposition of rare-earth oxides and NiO instead of RNiO3. The epitaxial films of nickelates were strained and consisted of 90° domains with the orthorhombic Pnma structure. The transport properties of the strained films on LaAlO3 were similar to those of the bulk material of the same composition under applied pressure of 9 kbar but they were different from the properties of the bulk material under ambient pressure. The result implies that transport properties of RNiO3 films with sharp metal-to-insulator transition can be effectively tuned by the control of the lattice strain.

A survey of the experimental results is given on the epitaxial thin film growth of various oxide phases in thermodynamic conditions J, P, Po-2 or composition) which are far from those which are necessary for the stable existance of these phases in polycristalline state. The in-bulk unstable phases BaCu3O4, NdMn7O12,, rare earth nickelates RNiO3 and in-bulk nonequilibrium phase assemblies in the systems R2O3 - CuO - BaO are the examples. The stabilizing effect in thin films was observed only when growing phase was coherent with the substrate or the surrounding matrix and the epitaxial growth was induced. The effect is thought to be not of kinetic origine but of thermodynamic one resulting from low surface energy of coherent interfaces.

Thin epitaxial films of (La1−xPrx)0.7Ca0.3MnO3 (x=0,0.25,0.5,0.75,1) were grown on (001) ZrO2(Y2O3) substrates by aerosol MOCVD at 750°C. The structure and electronic properties of the films were compared with those of the films on perovskite substrates and with ceramics of the same composition. The films on ZrO2(Y2O3) are (110) oriented and possess a varying in-plane orientation microstructure giving rise to an extremely high density of the large-angle boundaries (∼1011 cm−2). Above the maximum resistivity temperature Tp, the microstructure results in a ∼30 meV increase of the hopping energy of small polarons (∼130 meV) and suppression of the maximum of d ( log ρ/T)/ d (1/T) at the transition from Arrhenius like ( log ρ∝T −1 ) to Mott like ( log ρ∝T −1/4 ) temperature dependence of resistivity (ρ). Below Tp an empirical law log ρ=αT 2 + log ρ′ was derived indicating a thermally activated trapping of the itinerant charge carriers. Large-angle boundaries in the films on ZrO2(Y2O3) destabilize the ferromagnetic state and cause residual resistivity (ρ′) higher by a factor of 100 compared to the films on the perovskite substrates. They provide a reservoir for the tunnel magnetoresistance owing to the spin-polarized tunneling.

A new approach to the CVD of oxides with kinetically hindered diffusion, called volatile surfactant-assisted (VSA) metal-organic chemical vapor deposition (MOCVD), consisting of film deposition in the presence of a volatile low melting point oxide (Bi2O3) has been developed. The process was applied to the deposition of LaAlO3 films, and a model of the process was proposed. Epitaxial and textured LaAlO3 films on various substrates were obtained, both by thermal and VSA MOCVD. A marked improvement in crystalline quality and surface morphology was found for the films deposited by VSA MOCVD. LaAlO3 films obtained in the presence of Bi2O3 did not contain Bi. A significant increase (up to five times) of the deposition rate was observed for LaAlO3 films deposited by VSA MOCVD compared with that for the films grown by thermal MOCVD.

Superconducting (T-c= 38 K) thin films of (Pb,Cu)(2)(Ba,Pb)(2)YCu2Oy have been grown by MetalOrganic Chemical Vapor Deposition (MOCVD) on single crystal (001)LaAlO3 substrates in a single deposition run. The critical parameters for stabilizing lead-containing compounds in thin films are considered. It was found that a high vapor pressure of lead-containing species in the gas phase during the film growth determines the stability of formed compounds. The results of high-resolution transmission electron microscopy (HREM) and X-ray diffraction analysis (XRD) analyses of (Pb,Cu)(2)(Ba,Pb)(2)YCu2Oy thin films are presented. (C) 2000 Published by Elsevier Science B.V.