Y3Al5O12 (YAG) single crystals doped with vanadium ions (V3+) were obtained by the Czochralski method.
The X-ray photoelectron spectra of YAG:V annealed in reducing atmospheres: H2, vacuum and H2 + vacuum
are presented and compared with the spectra of the YAG ceramics. The X-ray photoelectron spectra showed
that the vanadium dopant concentration in YAG:V crystals is lower than a nominal one. For the \as grown"
YAG:2.8at.%V crystal vanadium exists in the mixed valence state. The increase in lattice parameters for the
samples annealed in hydrogen was found

Kruczek, Magdalena

Kusz, Joachim

Sakowska, H.

Talik, Ewa

Węglarz, H.

Świrkowicz, M.

Acta Physica Polonica A

English

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: Electronic Structure of Y3Al5O12:V Single Crystals, Comparison with Sintered Ceramics  Author: Magdalena Kruczek, Ewa Talik, Joachim Kusz, H. Sakowska, M. Świrkowicz, H. Węglarz  Citation style: Kruczek Magdalena, Talik Ewa, Kusz Joachim, Sakowska H., Świrkowicz M., Węglarz H. (2009). Electronic Structure of Y3Al5O12:V Single Crystals, Comparison with Sintered Ceramics. "Acta Physica Polonica A" (Vol. 115, nr 1 (2009), s. 209-212).  Vol. 115 (2009) ACTA PHYSICA POLONICA A No. 1Proceedings of the European Conference “Physics of Magnetism” (PM’08), Poznan´ 2008Electronic Structure of Y3Al5O12:V Single Crystals,Comparison with Sintered CeramicsM. Kruczeka,b, E. Talika, J. Kusza, H. Sakowskab, M. S´wirkowiczb and H. We¸glarzbaInstitute of Physics, University of SilesiaUniwersytecka 4, 40-007 Katowice, PolandbInstitute of Electronic Materials TechnologyWo´lczyn´ska 133, 01-919 Warsaw, PolandY3Al5O12 (YAG) single crystals doped with vanadium ions (V3+) were obtained by the Czochralski method.The X-ray photoelectron spectra of YAG:V annealed in reducing atmospheres: H2, vacuum and H2 + vacuumare presented and compared with the spectra of the YAG ceramics. The X-ray photoelectron spectra showedthat the vanadium dopant concentration in YAG:V crystals is lower than a nominal one. For the “as grown”YAG:2.8at.%V crystal vanadium exists in the mixed valence state. The increase in lattice parameters for thesamples annealed in hydrogen was found.PACS numbers: 33.60.+q, 33.70.Jg, 79.60.−i, 79.60.Bm1. IntroductionYAG:V3+ is one of the few known materials, whichshow a nonlinear absorption effect. Such materials areespecially attractive for Q-switching operation to obtainhigh peak power optical pulses [1]. Recently the YAG ce-ramics were synthesized to replace the YAG single crys-tals. These ceramics, which are characterized with sim-ilar to the YAG single crystals optical properties, wereobtained to increase the doping range, simplify tech-nological process and lower costs. Moreover, there ispossible obtaining of ceramics shapes with bigger sizethan single crystals grown by the Czochralski method [2].X-ray photoelectron spectroscopy (XPS) was used tostudy the chemical composition and electronic structureof the YAG:V single crystals. For comparison the ceram-ics were investigated.2. ExperimentalSingle crystals of YAG:V were grown with the use ofthe Czochralski method. The thermal system consistedof a 53 mm outer diameter, 50 mm high and 1.5 mm wallthickness iridium crucible, in passive iridium afterheaterplaced around the crucible top on the grog, and aluminaheat shields around the afterheater. A charge materialwas prepared on base of high purity oxides: Y2O3 (5.0N),Al2O3 (5.0N) and V2O5 (4.5N) as a dopant. The nominalconcentration of the V5+ ions was 0.8 and 2.8 at.%. Thegrowing atmosphere was pure nitrogen. The followingconditions of the growth processes were applied: growthrate 0.6–1.2 mm/h; rotation rate 5–20 rpm; cooling aftergrowth — at least 24 h. The obtained single crystalsup to 20 mm in diameter and 65–70 mm in length werefree of macroscopic defects and inclusions of other phases.An example of the “as grown” single crystal is shown inFig. 1.Fig. 1. An “as grown” YAG:V single crystal obtainedby the Czochralski method.Each crystal was sliced into wafers of about 1 mmthickness. A wafer from a middle part of the crystals wasused for examinations. The wafer of YAG:0.8at.%V wasdivided into four parts, which were annealed in reduc-tion atmospheres: (1) in hydrogen, at 1200◦C for 10 min;(2) in vacuum, at 1750◦C for 5 h; (3) first in hydrogenat 1200◦C for 10 min and next in vacuum, at 1750◦Cfor 5 h. After annealing the samples were slowly cooleddown to room temperature.Besides the single crystals the YAG ceramics were ob-tained. Ammonium hydrogen carbonate was applied asprecipitant for production of YAG nanopowders from so-(209)210 M. Kruczek et al.lution of nitrates. Powders were calcinated up to 1100◦C,milled, mixed in proper proportions for solid state reac-tion synthesis, and densified by isostatic pressing at thepressure of 200 MPa. Powder compacts were sinteredin vacuum (10−6 Tr) within the temperature range of1700–1780◦C and holding time up to 60 h. Several sam-ples were prepared with 0.5% of tetraethyl orthosilicate(TEOS) as sintering aid.The XPS spectra were obtained using a PHI 5700/660Physical Electronics Photoelectron Spectrometer withmonochromatized AlKα X-ray radiation (1486.6 eV). Allmeasurements were performed on the crystal broken un-der UHV conditions of 10−10 Tr. The binding energy wasdetermined with reference to the C 1s component set at284.6 eV. The Gaussian-Lorentzian functions were usedto fit the XPS core level spectra [3, 4]. The lattice pa-rameters of the YAG:V single crystals were studied at theroom temperature using a four-circle KM4 diffractometerwith graphite-monochromatized Mo Kα radiation.3. Results and discussionChanges of the lattice parameters after annealing pro-cesses for the nominal YAG:0.8at.%V samples and purestoichiometric YAG crystal were collected in Table I. Themeasurements show an increase in the lattice parametersfor the YAG samples doped with V ions in comparison tothe pure YAG crystal and another increase in lattice pa-rameters for the samples annealed in hydrogen. It seemsthat annealing in vacuum does not change the lattice pa-rameters.TABLE ILattice parameters of the YAG and different treatmentof YAG:0.8at.%V single crystal.Lattice parameters [A˚]YAG single crystals aYAG stoichiometric “as grown” transparent 12.0050(6)YAG:V “as grown” 12.0056(6)YAG:V annealed in H2 12.0071(7)YAG:V annealed in vacuum 12.0057(6)YAG:V annealed in H2 and vacuum 12.0082(7)The example XPS spectrum of the “as grown”YAG:2.8at.%V single crystal in a wide energy range isshown in Fig. 2. Table II shows the chemical composi-tion, calculated using the XPS spectra for the YAG:Vsingle crystals and YAG ceramics. All samples exhibitedan increased amount of oxygen and yttrium and reducedamount of aluminum in relation to the nominal value. Asin earlier measurements, lower content of aluminum ionsand excess of oxygen ions for “as grown” YAG:Yb crystalwas found [5]. The possible explanation is the presence ofthe YAG blocks separated by yttrium oxide layers. Sim-ilar type of structure is described in the literature as theRuddlesden–Popper phases [6]. Moreover, the annealingFig. 2. The XPS spectrum in the wide energy range ofthe “as grown” YAG:2.8at.%V single crystal.procedure did not remove the excess of oxygen markedly.TABLE IIChemical composition of the YAG:V single crystals andYAG ceramics.Chemical compositionY Al O V [at.%]YAG single crystalsYAG stoichiometric “as grown”transparent3.01 5.01 11.98YAG:0.8at.%V “as grown” 3.12 4.72 12.16YAG:0.8at.%V annealed in H2 3.11 4.75 12.14YAG:0.8at.%V annealed in vac-uum3.12 4.80 12.08YAG:0.8at.%V annealed in H2and vacuum3.12 4.79 12.09YAG:2.8at.%V “as grown” 3.07 4.80 12.13 0.71YAG ceramics “as grown”YAG stoichiometric transparent 3.01 4.99 12.00YAG non-transparent 3.09 4.79 12.13YAG with 0.5% TEOS non-transparent3.13 4.78 12.08The XPS studies showed for the all YAG:0.8at.%Vcrystal samples the amount of vanadium is below thelimit of the sensitivity of the method. For the “as grown”YAG:2.8at.%V crystal the amount of vanadium is lowerin relation to the nominal one. The vanadium 2p statesare split due to spin–orbit interaction into two linesV 2p3/2–V 2p1/2 with energy splitting ∆ = 7.6 eV andintensity ratio I(2p3/2)/I(2p1/2) = 2/1 (Fig. 3). A de-convolution of the V 2p showed two components relatedto V3+ and V5+. The first line (M) in V 2p3/2 related tothe V3+ component was at 515.7 eV. Such binding energyElectronic Structure of Y3Al5O12:V Single Crystals . . . 211Fig. 3. The V 2p line of the “as grown” YAG:2.8at.%Vsingle crystal.was confirmed by XPS measurements of the V 2p line inV2O3 [3]. The second line (S) related to the V5+ wasat 517.4 eV as in V2O5 [3]. The ratio of areas betweenadditional (S) and main (M) lines was 0.27.The Y 3d, Al 2p, and O 1s lines were deconvoluted af-ter a background subtraction and example spectra wereshown in Fig. 4. The Y 3d and Al 2p lines are decom-posed into two lines split due to spin–orbit interactions:Y 3d5/2–Y 3d3/2 with splitting energy ∆ = 2.02 eV, theintensity ratio I(3d5/2)/I(3d3/2) = 3/2 and Al 2p3/2–Al 2p1/2 with ∆ = 0.45 eV, I(2p3/2)/I(2p1/2) = 2/1.The binding energies of these elements are not signif-icantly changed for all samples and they are approxi-mately Y 3d5/2 = 157.3 eV, Y 3d3/2 = 159.3 eV, Al2p3/2 = 73.35 eV, Al 2p1/2 = 73.8 eV and O 1s =530.15 eV. The analysis of the O 1s lines shows that theintensity of the additional line at lower binding energy forthe “as grown” crystal after annealing disappeared. Thisis caused by improvement of the crystal structure afterthe annealing process. The XPS lines for the samples an-nealed are narrower and better split and valence bandsshow less broadening towards the Fermi level suggestingless defects present in the structure. Moreover, in com-parison with the YAG:V single crystals all XPS lines forthe YAG ceramics are narrower and better split, even incomparison with annealed crystals. This indicates betterquality of the crystal structure for ceramics.Fig. 4. The Y 3d, Al 2p, O 1s lines and valence bands of the YAG:0.8at.%V single crystal and YAG ceramics.4. Conclusions• The aluminium deficiency, yttrium and oxygen ex-cess for the all measured samples was found.• The vanadium dopant in the “as grown”YAG:2.8at.%V crystal exists in the mixed valencestate and was lower than a nominal one. The totalV3+ and V5+ dopant concentration was determinedas 0.7at.%.• The amount of vanadium in the YAG:0.8at.%Vcrystal was below the limit of the sensitivity of themethod.212 M. Kruczek et al.• The lattice parameters changes for annealing in hy-drogen were observed.AcknowledgmentsWe would like to thank the Director, Institute ofElectronic Materials Technology, Dr. Z. ÃLuczyn´ski forhis support of this research. This work is partly sup-ported by Materialwissenschaftliches Forschungzentrumder Universita¨t Mainz, Germany.References[1] Z. Mierczyk, Z. Frukacz, Opto-Electron. Rev. 1, 67(2000).[2] K. Ueda, J. Lu, Laser Phys. 11, 1053 (2001).[3] J. Moulder, W. Stickle, P. Sobol, K. Bomben, Hand-book of X-ray Photoelectron Spectroscopy, PhysicalElectronics, Minnesota 1995.[4] Multipak Software Version 6, Physical Electronics,Minnesota 1998.[5] M. Kruczek, E. Talik, H. Sakowska, M. GaÃla,M. S´wirkowicz, Cryst. Res. Technol. 40, 439 (2005).[6] S.N. Ruddlesden, P. Popper, Acta Crystallogr. 11, 54(1958).

Electronic Structure of Y3Al5O12:V Single Crystals, Comparison with Sintered Ceramics

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Electronic Structure of Y3Al5O12:V Single Crystals, Comparison with Sintered Ceramics

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