ARTICLE pubs.acs.org/crystal
Structural and Electronic Properties of ZnWO4(010) Cleaved Surface Victor V. Atuchin,*,† Evgeny N. Galashov,‡ Oleg Yu. Khyzhun,§ Anton S. Kozhukhov,#,^ Lel D. Pokrovsky,† and Vladimir N. Shlegel‡ †
Laboratory of Optical Materials and Structures, Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Science, Novosibirsk 90, 630090, Russia ‡ Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 90, 630090, Russia § Frantsevich Institute for Problems of Materials Science, National Academy of Sciences of Ukraine, 3 Krzhyzhanivsky Street, Kiev UA-03142, Ukraine # Laboratory of Nanodiagnostics and Nanolithography, Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 90, 630090, Russia ^ Physical Department, Novosibirsk State University, Novosibirsk 90, 630090, Russia ABSTRACT: A high-quality inclusion-free ZnWO4 crystal 90 mm in diameter and with a mass of up to 8 kg was grown by the low thermal gradient Czochralski technique. Crystallographic properties of ZnWO4(010) cleaved surfaces were evaluated with reflection high energy electron diffraction (RHEED), and the electronic structure of the surface was studied using X-ray photoelectron spectroscopy (XPS). A system of Kikuchi lines was observed for cleaved ZnWO4(010) by RHEED confirming the high crystallographic state of the surface. The XPS valenceband and core-level spectra of ZnWO4(010) have been measured. The XPS measurements reveal that tungsten and zinc atoms are in the formal valences þ6 and þ2, respectively, on cleaved ZnWO4(010) surface. The 3.0 keV Arþ bombardment of the surface causes partial transformation of tungsten ions from W6þ to lower valence states; however, no partial loss of oxygen atoms belonging to ZnO6 octahedra occurs due to this bombardment of the ZnWO4(010) surface because after this treatment zinc remains exclusively in the formal valence þ2. The WO chemical bonding is considered in tungstates including ZnWO4.
’ INTRODUCTION Bivalent metal tungstates with common composition A2þWO4 crystallize in a wolframite-type structure with space group P2/c at an ionic radius rA2þ < 77 pm. Such tungstates are chemically stable and are spread in nature as minerals. The tungstates can be synthesized by different chemical routes and can be grown as high-quality single crystals.18 Wolframite-type tungstates are widely used in nanotechnologies,1,4,9 photocatalysis,3,1012 electronics,4 laser techniques13,14 and as effective scintillator materials.1518 Zinc tungstate, ZnWO4, relates to wolframite-type crystals A2þWO4 and is characterized by structural parameters of a = 4.6902(1) Å, b = 5.7159(1) Å, c = 4.9268(1) Å, β = 90.626(1), V = 132.14(1) Å3, Z = 2.19 The crystal structure of ZnWO4 is shown in Figure 1. The structure is formed by edge-sharing zigzag chains of distorted ZnO6 and WO6 octahedra. The ZnWO4 crystals are characterized by good cleavage properties of the (010) planes, and this can be used for the preparation of single crystal substrates with high-quality surface. The present work is aimed at studying the electronic structure of the ZnWO4 compound in detail with X-ray photoelectron spectroscopy (XPS). Earlier, only the electronic structure of the valence band of ZnWO4 was evaluated by theoretical and experimental methods.20,21 The influence of middle-energy Arþ bombardment on the valence-band and constituent element core levels will be also r 2011 American Chemical Society
evaluated because this method of surface cleaning is applied in epitaxial technologies. Previously, electronic parameters of several complex tungstates were defined with the XPS method. It is well-known that the energy position of the element core level is an indicator of the ionicity of the chemical bonds between cations and anions in the crystal lattice. This study attempts to relate the binding energy (BE) values of W 4f7/2 and O 1s core levels with mean chemical bond length L(WO) in complex tungstates accounting recent XPS measurements for wolframite-type tungstates.
’ RESULTS AND DISCUSSION High-quality inclusion-free ZnWO4 crystals were grown at the Nikolaev Institute of Inorganic Chemistry, Siberian Branch of the Russian Academy of Sciences (NIIC SB RAS) by the low thermal gradient Czochralski technique (LTG Cz).7,8 In this method, thermal gradient in the melt is confined at a level of no more than ∼1 C/cm, the charge use factor reaches ∼95%, and grown crystals have perfect quality. Previously, to elaborate the LTG Cz technique at NIIC SB RAS, the crystals of Bi4Ge3O12 with a mass Received: February 26, 2011 Revised: April 4, 2011 Published: April 20, 2011 2479
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Figure 1. Crystal structure of ZnWO4. Unit cell is outlined.
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Figure 3. AFM pattern recorded for ZnWO4(010) cleaved surface. The area of 12 12 μm2 is shown.
Figure 4. Kikuchi lines pattern observed by RHEED for cleaved ZnWO4(010) surface. Figure 2. ZnWO4 crystals grown by the LTG Cz technique.
of up to 56 kg and CdWO4 with a mass of up to 12 kg were grown successfully. We see no essential difficulties in further increasing the crystal size. In experiments with ZnWO4 crystal growth the laboratory puller HX-620 with weight monitoring and computer control of the process was used. The resolution of the weighing sensor was (20 mg for the load of 10 kg. A three-zone furnace with resistive heating elements was used as the thermal unit. Temperature fluctuations during the growth process were not exceeding (0.05 C. Crystal growth was performed in the air from a platinum crucible 120 mm in diameter and 290 mm high, covered with a cap equipped with a pipe through which the pulling rod with a seed was introduced into the crystallization zone. The crystal remains inside the crucible during the entire process. The starting materials for charge preparation were pure oxides WO3 (99.999%) made at the NIIC SB RAS and ZnO (99.995%) manufactured by Umicore (Belgium). The solid-phase synthesis was carried out directly into the crystal growth system at a temperature T = 1000 C during t = 12 h. The crystals were grown along the [010] direction. The rate of crystallization was from 0.5 to 1.0 mm/h and
Figure 5. XPS survey spectra of (1) pristine and (2) Arþ-irradiated ZnWO4(010) cleaved surface. 2480
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Table 1. Binding Energies of Constituent Element Core Levels and Auger Lines of ZnWO4 BE, eV core level
Arþ-irradiated
ZnWO4 film
ZnWO4 nano
pristine
Arþ-irradiated
Zn 3d
∼8
10.8
10.75
W 4f7/2
∼33
∼35.1
35.6
35.95
35.75
W 4f5/2
∼35
∼37.3
37.8
38.05
37.8
89.2
89.15
Zn 3p3/2 Zn 3s
140.1
140.1
Zn L2M45M45
241.8
241.9
W 4d5/2
248.1
247.5
W 4d3/2 Zn L3M45M45
261.7 264.9
261.6 264.8
fixed at 284.6
C 1s Zn L2M23M45(1P)
329.2
329.3
Zn L3M23M45(3P)
343.5
343.6
Zn L3M23M45(1P)
352.3
352.4
∼530.1
O 1s
530.6
530.95
530.9
O KL1L23
762.8
762.7
O KL23L23 O KL1L1
742.7 ?
742.6 776.5
∼1019
Zn 2p3/2 Zn 2p1/2 ref
19
22
Figure 6. XPS W 4f and Zn 3d core-level spectra (including the valenceband region) of (1) pristine and (2) Arþ-irradiated ZnWO4(010) cleaved surface.
the rotational rate was 15 rpm. After growth, the crystal was cooled to room temperature at 50 C/h. In a result, crystals 90 mm in diameter and mass of up to 8 kg were grown. Several crystals of ZnWO4 grown by the LTG Cz technique are shown in Figure 2. A parallelepiped-like sample of ZnWO4 was cut with the edges directed along the crystallographic axes. The substrates of ZnWO4 (010) with dimensions 12 0.7 12 mm3 were prepared by cleaving the sample with a steel knife. Surface micromorphology of the substrates was studied by atomic force microscopy (AFM) with a Solver P-47H device in noncontact mode. Top-surface crystallographic properties
9
1022.3
1022.1
1045.4
1045.2
this study
this study
Figure 7. XPS O 1s core-level spectra of (1) pristine and (2) Arþirradiated ZnWO4(010) cleaved surface.
were evaluated with RHEED using an EFZ4 device under electron energy of 50 keV. Electronic properties of the ZnWO4(010) surface were characterized by X-ray photoelectron spectroscopy (XPS). XPS valenceband and core-level spectra of ZnWO4 were measured using the UHV-Analysis-System assembled by SPECS (Germany). The system is equipped with a PHOIBOS 150 hemispherical analyzer. A base pressure of a sublimation ion-pumped chamber of the system was less than 6 1010 mbar during the present experiments. The Mg KR radiation (E = 1253.6 eV) was used as a source of XPS spectra excitation. The XPS spectra were recorded at a constant pass energy of 25 eV. The energy scale of the spectrometer was calibrated 2481
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by setting the measured Au 4f7/2 and Cu 2p3/2 binding energies to 84.00 ( 0.05 eV and 932.66 ( 0.05 eV, respectively, with respect to the Fermi energy, EF. Energy drift due to charging effects was calibrated taking the C 1s (284.6 eV) core-level spectrum of adventitious hydrocarbons. To remove surface contaminations, a bombardment of crystal surface has been performed by Arþ ions with energy of 3.0 keV during 5 min at an ion current density of 15 μA/cm2. AFM pattern recorded for cleaved ZnWO4(010) surface is shown in Figure 3. The surface is formed by flat parallel terraces
with scattered mesoscale structural defects. The height of the elemental step of ∼0.6 ( 0.1 nm is close to the cell parameter b of ZnWO4. The result of RHEED observation is presented in Figure 4. As one can see from the figure, a system of Kikuchi lines is a characteristic of the surface under study. This RHEED pattern indicates a high crystallographic quality of the cleaved ZnWO4(010) surface. Survey XPS spectra of the above surface are shown in Figure 5. From the figure, it is obvious that all the spectral features, except the C 1s level, are attributed to the constituent element core-levels or Auger lines of zinc tungstate. The presence of the C 1s line in the survey XPS spectrum of untreated ZnWO4(010) is due to the hydrocarbons adsorbed on the surface. However, as the survey XPS spectrum reveals (Figure 5, curve 1), the intensity of the C 1s corelevel line is rather low for the pristine cleaved ZnWO4(010) surface, and the 3.0 keV Arþ-irradiation causes almost complete elimination of the C 1s line in the survey XPS spectrum (Figure 5, curve 2). Total set of binding energies of core levels and Auger lines measured for ZnWO4 is presented in Table 1. Figure 6 shows the XPS W 4f core-level spectrum (including also the XPS Zn 3d and valence-band spectra), while the O 1s and Zn 2p core-level spectra of ZnWO4(010) surface are presented in Figures 7 and 8, respectively. From Figures 6 and 8, it is apparent that the XPS W 4f and Zn 2p core-level spectra of pristine cleaved ZnWO4(010) surface are simple spin-doublets with the XPS W 4f7/2 and Zn 2p3/2 binding energies corresponding to those of tungsten and zinc in the formal valences þ6 and þ2, respectively.23 From the chemical analysis (Table 2) of the pristine ZnWO4(010) surface as determined using XPS data of Zn 2p3/2, W 4f7/2, and O 1s peaks and atomic sensitivity factors,24 it is obvious that the chemical stoichiometry and concentration of individual elements of the zinc tungstate under study are rather well maintained. The 3.0 keV Arþ bombardment alters significantly the chemical composition of the ZnWO4(010) surface. Partial transformation of tungsten ions from W6þ to lower valence states (mainly W0)25 with induction of additive electronic states at the top of the valence band is carried out. From the survey XPS spectra (Figure 5), one can conclude that partial loss of oxygen on the
Figure 8. XPS Zn 2p core-level spectra of (1) pristine and (2) Arþirradiated ZnWO4(010) cleaved surface.
Table 2. Relative Element Concentration at the ZnWO4(010) Surface element
Zn
W
O
pristine surface
15.3
16.4
68.3
ZnWO4 (nominal)
16.7
16.7
66.6
Table 3. Structural and Electronic Parameters of Inorganic Tungstates compound
a
L(WO), pm
ref
BE(O 1s), eV
BE(W 4f7/2), eV
Δ(OW), eV
ref
NiWO4
195.6
35
531.5
35.2
496.3
44
CuWO4
194.7
36
530.6
35.5
495.1
45
R-SnWO4
194.4
37
530.5
35.5
495.0
46
FeWO4
194.0
38
530.6
35.6
495.0
4
530.3
35.1
495.2
47
CoWO4
193.9
35
530.7
35.7
495
4
CaWO4
178.4
39
530.3 530.1
34.8 35.1
495.5 495.0
48 49
SrWO4
177.9
40
529.9
35.5
494.4
50
β-PbWO4
179.5
41
530.7
35.4
495.3
51
KGd(WO4)2
195.9
42
530.1
35.2
494.9
52
KGd0.95Nd0.05(WO4)2
195.9a
42
530.3
35.2
495.1
29
KY(WO4)2
196.0
43
530.8
35.3
495.5
53
ZnWO4
194.2
19
530.6
35.6
495.0
9
530.1 530.95
35.1 35.95
495.0 495.0
22 this study
Taken to be the same as for KGd(WO4)2 2482
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Figure 9. Dependence of Δ(OW) on L(WO) for tungstates.
ZnWO4(010) surface occurs at such an Arþ bombardment, and this treatment leads to the removal of oxygen atoms which are in the nearest surrounding of tungsten atoms (WO6 octahedra). This partial loss of oxygen belonging to WO6 octahedra, due to the Arþ bombardment, causes a little shift of tungsten core-level spectra toward lower binding energies as data listed in Table 1 reveal. No partial loss of oxygen atoms belonging to ZnO6 octahedra occurs due to 3.0 keV Arþ bombardment of the ZnWO4(010) surface. After this bombardment, zinc remains exclusively in the formal valence þ2 as Figure 8 indicates. The Arþ bombardment of the ZnWO4(010) surface does not cause changes of the XPS core-level binding energies of zinc and oxygen atoms, and the position of the maxima of Auger lines of these atoms remains unchanged (Table 1). Core level photoelectron spectroscopy is among direct methods applicable for chemical bonding characterization in complex oxides. On the oxide bond formation, the valence electrons are shifted from metal to oxygen that results in great variation of electrical screening of inner shells with variation of BE of inner electrons. This effect can be detected as a variation in the core level BE in XPS spectra. It is interesting to consider WO chemical bonding in A2þWO4 compounds using BE values measured for O 1s and W 4f7/2 lines. Mean chemical bond length L(WO) calculated using crystal structural data is taken as a structural parameter. BE difference Δ(OW) = BE(O 1s) BE(W 4f7/2) is applied for chemical bonding characterization because the BE difference is a more robust parameter insensitive to BE scale shifts due to dielectric surface charging typical for oxides.2634 So, a collection of structural and electronic parameters of A2þWO4 oxides is shown in Table 3. Several compounds related to the KGd(WO4)2 family are also added for comparison. A diagram with these tungstates is shown in Figure 9. The tungstates show the Δ(OW) dominantly in the range of 494.9495.5 eV with two exceptions for NiWO4 and SrWO4.44,50 It should be noted that a very similar value Δ(OW) = 494.8 eV was earlier found for monoclinic, m-WO3, and hexagonal, h-WO3, modifications of tungsten oxide.54,55 An unreasonably high value of Δ(OW) reported in NiWO4 seems to have appeared due to powder surface hydration resulting in overestimated BE (O 1s). A source of very low Δ(OW) in SrWO4 is unclear. Generally, there is no strong dependence of (WO) bond ionicity on the coordination of W6þ ions by oxygens.
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As can be concluded for structural properties of (010) cleaved surface of a high-quality inclusion-free ZnWO4 crystal, the RHEED pattern indicates a system of Kikuchi lines confirming the high crystallographic state of the surface. The XPS core-level measurements reveal that tungsten and zinc atoms on cleaved ZnWO4(010) surfaces are in the formal valences þ6 and þ2, respectively. The 3.0 keV Arþ bombardment of the surface causes partial loss of oxygen atoms belonging to WO6 octahedra and causes partial transformation of tungsten ions from W6þ to lower valence states. However, no partial loss of oxygen atoms belonging to ZnO6 octahedra occurs due to this bombardment, and after this treatment zinc remains on the ZnWO4(010) surface exclusively in the formal valence þ2. This information permits classification of the ZnWO4(010) cleaved surface as a promising substrate material for epitaxial technologies if a suitable method is found to eliminate the mesodefects at the cleaved surface. High temperature annealing in an oxygencontaining atmosphere should be tested for this purpose because this treatment yielded good results on defect regrowing for many oxide crystals.
’ AUTHOR INFORMATION Corresponding Author
*Phone: þ7 (383) 3308889. Fax: þ7 (383) 3332771. E-mail:
[email protected].
’ REFERENCES (1) Liao, H.-W.; Wang, Y.-F.; Liu, X.-M.; Li, Y.-D.; Qian, Y.-T. Chem. Mater. 2000, 12, 2819–2821. (2) Kloprogge, J. T.; Weier, M. L.; Duong, L. V.; Frost, R. L. Mater. Chem. Phys. 2004, 88, 438–443. (3) Tong, W.; Li, L.; Hu, W.; Yan, T.; Li, G. J. Phys. Chem. C 2010, 114, 1512–1519. (4) Rajagopal, S.; Nataraj, D.; Khyzhun, O. Yu.; Djaoued, Y.; Robichaud, J.; Mangalaraj, D. J. Alloys Compd. 2010, 493, 340–345. .; (5) Pisarevskii, Yu. V.; Silvestrova, I. M.; Voszka, R.; Peter, A F€ oldvari, I.; Janszky, J. Phys. Status Solidi A 1988, 107, 161–164. (6) Wang, H.; Medina, F. D.; Zhou, Y. D.; Zhang, Q. N. Phys. Rev. B 1992, 45, 10356–10362. (7) Galashov, E. N.; Gusev, V. A.; Shlegel, V. N.; Vasiliev, Ya. V. Funct. Mater. 2009, 16, 63–66. (8) Galashov, E. N.; Gusev, V. A.; Shlegel, V. N.; Vasiliev, Ya. V. Cryst. Rep. 2009, 54, 689–691. (9) Bi, J.; Wu, L.; Li, Z.; Ding, Z.; Wang, X.; Fu, X. J. Alloys Compd. 2009, 480, 684–688. (10) Yu, C.; Yu, J. C. Mater. Sci. Eng., B 2009, 164, 16–22. (11) Zhao, X.; Liu, H.; Qu, J. Catal. Commun. 2010, 12, 76–79. (12) Chen, S.; Sun, S.; Sun, H.; Fan, W.; Zhao, X.; Sun, X. J. Phys. Chem. C 2010, 114, 7680–7688. (13) Kaminskii, A. A.; Eichler, H. J.; Ueda, K.; Klassen, N. V.; Redkin, B. S.; Li, L. E.; Findeisen, J.; Jaque, D.; García-Sole, J.; Fernandez, J.; Balda, R. Appl. Opt. 1999, 38, 4533–4547. (14) Eichler, H. J.; Gad, G. M. A.; Kaminskii, A. A.; Rhee, H. J. Zhejiang Univ. Sci. 2003, 4, 241–253. (15) Danevich, F. A.; Chernyak, D. M.; Dubovik, A. M.; Grinyov, B. V.; Henry, S.; Kraus, H.; Kudovbenko, V. M.; Mikhailik, V. B.; Nagornaya, L. L.; Podviyanuk, R. B.; Polischuk, O. G.; Tupitsyna, I. A.; Vostretsov, Yu. Ya. Nucl. Instrum. Meth. Phys. Res. A 2009, 608, 107–115. (16) Dubovik, A. M.; Vostretsov, Yu. Ya.; Grinyov, B. V.; Danevich, F. A.; Kraus, H.; Nagornaya, L. L.; Mikhailik, V. B.; Tupitsyna, I. A. Acta Phys. Pol., A 2010, 117, 15–19. (17) Belli, P.; Bernabei, R.; Cappella, F.; Cerulli, R.; Danevich, F. A.; Dubovik, A. M.; d’Angelo, S.; Galashov, E. N.; Grinyov, B. V.; Incicchitti, A.; Kobychev, V. V.; Nagornaya, L. L.; Nisi, S.; Nozzoli, F.; Poda, D. V.; 2483
dx.doi.org/10.1021/cg200265p |Cryst. Growth Des. 2011, 11, 2479–2484
Crystal Growth & Design Podviyanuk, R. B.; Prosperi, D.; Shlegel, V. N.; Tretyak, V. I.; Vasiliev, Ya. V.; Vostretsov, Yu. Ya. Acta Phys. Pol., A 2010, 117, 139–142. (18) Belli, P.; Bernabei, R.; Boiko, R. S.; Brudanin, V. B.; Bukilic, N.; Cerulli, R.; Chernyak, D. M.; Danevich, F. A.; d’Angelo, S.; Degoda, V. Ya.; Dossovitskiy, A. E.; Galashov, E. N.; Hyzhnyi, Yu.A.; Ildyakov, S. V.; Incicchitti, A.; Kobychev, V. V.; Kolesnyk, O. S.; Kovtun, G. P.; Kudovbenko, V. M.; de Laeter, J. R.; Mikhlin, A. L.; Nagorny, S. S.; Nedilko, S. G.; Nikolaiko, A. S.; Nisi, S.; Poda, D. V.; Podviyanuk, R. B.; Polischuk, O. G.; Prosperi, D.; Shcherban, A. P.; Shcherbatskyi, V. P.; Shlegel, V. N.; Solopikhin, D. A.; Stenin, Yu.G.; Tretyak, V. I.; Vasiliev, Ya.V.; Virich, V. D. Nucl. Instrum. Meth. Phys. Res. A 2010, 615, 301–306. (19) Trots, D. M.; Senyshyn, A.; Vasylechko, L.; Niewa, R.; Vad, T.; Mikhailik, V. B.; Kraus, H. J. Phys.: Condens. Matter 2009, 21, 325402. (20) Itoh, M.; Fujita, N.; Inabe, Y. J. Phys. Soc. Jpn. 2006, 75, 084705. (21) Kalinko, A.; Kuzmin, A.; Evarestov, R. A. Solid State Commun. 2009, 149, 425–428. (22) Zhao, X.; Zhu, Y. Environ. Sci. Technol. 2006, 40, 3367–3372. (23) Moulder, J. F.; Stickle, W. E.; Sobol, P. E.; Bomben, K. E. Handbook of X-Ray Photoelectron Spectroscopy; Chastian, J., Ed.; Perkin-Elmer: Eden Prairie, MN, 1992. (24) Practical Surface Analysis, 2nd ed.; Auger and X-ray Photoelectron Spectroscopy; Briggs, D., Seah, M. P., Eds.; New York, John Wiley & Sons Ltd., 1990; Vol. 1, pp 635638. (25) Khyzhun, O. Yu. J. Alloys Compd. 2000, 305, 1–6. (26) Atuchin, V. V.; Pokrovsky, L. D.; Kesler, V. G.; Maklakova, N. Yu.; Voronkova, V. I.; Yanovskii, V. K. Surf. Rev. Lett. 2004, 11, 191–198. (27) Atuchin, V. V.; Kalabin, I. E.; Kesler, V. G.; Pervukhina, N. V. J. Electron Spectrosc. Relat. Phenom. 2005, 142, 129–134. (28) Atuchin, V. V.; Kesler, V. G.; Pervukhina, N. V.; Zhang, Z. J. Electron Spectrosc. Relat. Phenom. 2006, 152, 18–24. (29) Atuchin, V. V.; Kesler, V. G.; Maklakova, N. Yu.; Pokrovsky, L. D.; Sheglov, D. V. Eur. Phys. J. B 2006, 51, 293–300. (30) Atuchin, V. V.; Alekseeva, O. A.; Kesler, V. G.; Pokrovsky, L. D.; Sorokina, N. I.; Voronkova, V. I. J. Solid State Chem. 2006, 179, 2349–2355. (31) Ramana, C. V.; Atuchin, V. V.; Kesler, V. G.; Kochubey, V. A.; Pokrovsky, L. D.; Shutthanandan, V.; Becker, U.; Ewing, R. C. Appl. Surf. Sci. 2007, 253, 5368–5374. (32) Ramana, C. V.; Atuchin, V. V.; Becker, U.; Ewing, R. C.; Isaenko, L. I.; Khyzhun, O. Yu.; Merkulov, A. A.; Pokrovsky, L. D.; Sinelnichenko, A. K.; Zhurkov, S. A. J. Phys. Chem. C 2007, 111, 2702–2708. (33) Atuchin, V. V.; Kesler, V. G.; Pervukhina, N. V. Surf. Rev. Lett. 2008, 15, 391–399. (34) Atuchin, V. V.; Grivel, J.-C.; Zhang, Z. Chem. Phys. 2009, 360, 74–78. (35) Weitzel, H. Z. Kristallogr. 1976, 144, 238–258. (36) Schofield, P. F.; Knight, K. S.; Redfern, S. A. T.; Cressey, G. Acta Crystallogr. B 1997, 53, 102–112. (37) Jeitschko, W.; Sleight, A. W. Acta Crystallogr. B 1974, 30, 2088–2094. (38) Ulku, D. Z. Kristallogr. 1967, 124, 192–219. (39) Hazen, R. M.; Finger, L. W.; Mariathasan, J. W. E. J. Phys. Chem. Solids 1985, 46, 253–263. (40) G€urmen, E.; Daniels, E.; King, J. S. J. Chem. Phys. 1971, 55, 1093–1097. (41) Moreau, J. M.; Galez, P.; Peigneux, J. P.; Korzhik, M. V. J. Alloys Compd. 1996, 238, 46–48. (42) Pujol, M; Sole, R.; Massons, J.; Gavalda, J.; Solans, X.; Zaldo, C.; Diaz, F.; Aguilo, M. J. Appl. Phys. 2001, 34, 1–6. (43) Gallucci, E.; Goutaudier, C.; Boulon, G.; Cohen-Addad, M. T.; Mentzen, B. F. J. Cryst. Growth 2000, 209, 895–905. (44) Ng, K. T.; Hercules, D. M. J. Phys. Chem. 1976, 80, 2094–2102. (45) Khyzhun, O. Yu.; Strunskus, T.; Cramm, S.; Solonin, Yu. M. J. Alloys Compd. 2005, 389, 14–20. (46) Dong, H.; Li, Z.; Ding, Z.; Pan, H.; Wang, X.; Fu, X. Sens. Actuat. B 2009, 140, 623–628.
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(47) Zhou, Y.-X.; Yao, H.-B.; Zhang, Q.; Gong, J.-Y.; Llu, S.-J.; Yu, S.-H. Inorg. Chem. 2009, 48, 1082–1090. (48) Wang, W.; Yang, P.; Gai, S.; Niu, N.; He, F.; Lin, J. J. Nanopart. Res. 2010, 12, 2295–2305. (49) Nefedov, V. I. J. Electron Spectrosc. Relat. Phenom. 1982, 25, 29–47. (50) Chen, L.; Gao, Y. Mater. Res. Bull. 2007, 42, 1823–1830. (51) Charton, P.; Gengembre, L.; Armand, P. J. Solid State Chem. 2002, 168, 175–183. (52) Atuchin, V. V.; Kesler, V. G.; Maklakova, N. Yu.; Pokrovsky, L. D. Solid State Commun. 2005, 133, 347–351. (53) Atuchin, V. V.; Pokrovsky, L. D.; Khyzhun, O. Yu.; Sinelnichenko, A. K.; Ramana, C. V. J. Appl. Phys. 2008, 104, 033518. (54) Khyzhun, O. Yu.; Solonin, Yu. M.; Dobrovolsky, V. D. J. Alloys Compd. 2001, 320, 1–6. (55) Solonin, Yu. M.; Khyzhun, O. Yu.; Graivoronskaya, E. A. Cryst. Growth Des. 2001, 1, 473–477.
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