Sol-gel synthesis and characterization of lanthanide aluminium garnets ; Lantanoidų aliuminio granatų sintezė zolių-gelių metodu ir apibūdinimas

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VILNIUS UNIVERSITY INSTITUTE OF CHEMISTRY, CENTER FOR PHYSICAL SCIENCES AND TECHNOLOGY Natalija Dubnikova SOL-GEL SYNTHESIS AND CHARACTERIZATION OF LANTHANIDE ALUMINIUM GARNETS Summary of doctoral dissertation Physical sciences, Chemistry (03 P) Vilnius, 2011 The work was carried out in Vilnius University in the period 2007–2011. Scientific supervisors: Doc. dr. Darius Jasaitis (Vilnius University, Physical Sciences, Chemistry - 03 P); (2007–2010 m.); Prof. habil. dr. Aivaras Kareiva (Vilnius University, Physical Sciences, Chemistry - 03 P); (2010–2011 m.). Evaluation board: Chairman: Prof. habil. dr. Rimantas Ramanauskas (Center for Physical Sciences and Technology, Institute of Chemistry, Physical Sciences, Chemistry - 03 P). Members: Doc. dr. Ingrida Ancutienė (Kaunas University of Technology, Physical Sciences, Chemistry - 03 P); Doc. dr. Virgaudas Kubilius (Vilnius University, Physical Sciences, Chemistry - 03 P); Prof. habil. dr. Antanas Laukaitis (Vilnius Gediminas Technical University, Institute of Thermal Insulation, Technological Sciences, Materials Engineering - 08 T); Doc. dr. Jūratė Senvaitienė (P. Gudynas Centre for Restoration, Physical Sciences, Chemistry - 03 P). Official opponents: Dr. Irma Bogdanovičienė (Vilnius University, Physical Sciences, Chemistry - 03 P); Prof. dr.

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VILNIUS UNIVERSITY

INSTITUTE OF CHEMISTRY, CENTER FOR PHYSICAL SCIENCES
AND TECHNOLOGY












Natalija Dubnikova



SOL-GEL SYNTHESIS AND CHARACTERIZATION OF
LANTHANIDE ALUMINIUM GARNETS







Summary of doctoral dissertation

Physical sciences, Chemistry (03 P)














Vilnius, 2011

The work was carried out in Vilnius University in the period 2007–2011.
Scientific supervisors:
Doc. dr. Darius Jasaitis (Vilnius University, Physical Sciences, Chemistry - 03 P);
(2007–2010 m.);
Prof. habil. dr. Aivaras Kareiva (Vilnius University, Physical Sciences, Chemistry - 03
P); (2010–2011 m.).

Evaluation board:
Chairman:
Prof. habil. dr. Rimantas Ramanauskas (Center for Physical Sciences and Technology,
Institute of Chemistry, Physical Sciences, Chemistry - 03 P).
Members:
Doc. dr. Ingrida Ancutienė (Kaunas University of Technology, Physical Sciences,
Chemistry - 03 P);
Doc. dr. Virgaudas Kubilius (Vilnius University, Physical Sciences, Chemistry - 03 P);
Prof. habil. dr. Antanas Laukaitis (Vilnius Gediminas Technical University, Institute of
Thermal Insulation, Technological Sciences, Materials Engineering - 08 T);
Doc. dr. Jūratė Senvaitienė (P. Gudynas Centre for Restoration, Physical Sciences,
Chemistry - 03 P).
Official opponents:
Dr. Irma Bogdanovičienė (Vilnius University, Physical Sciences, Chemistry - 03 P);
Prof. dr. Raimundas Šiaučiūnas (Kaunas University of Technology, Technological
Sciences, Chemical Engineering - 05 T).


The official discussion will be held on 2 p.m. 16 December 2011 at the meeting of the
Evaluation Board at the Auditorium of Inorganic Chemistry of the Faculty of Chemistry
of Vilnius University.
Address: Naugarduko 24, LT-03225 Vilnius, Lithuania. Tel. 2193108. Fax: 2330987.
The summary of doctoral dissertation was mailed on the …. of November 2011.
The dissertation is available at the Library of Vilnius University and at the Library of
Institute of Chemistry CPST.

VILNIAUS UNIVERSITETAS

FIZINIŲ IR TECHNOLOGIJOS MOKSLŲ CENTRO CHEMIJOS
INSTITUTAS












Natalija Dubnikova



LANTANOIDŲ ALIUMINIO GRANATŲ SINTEZĖ
ZOLIŲ-GELIŲ METODU IR APIBŪDINIMAS







Daktaro disertacija
Fiziniai mokslai, chemija (03 P)













Vilnius, 2011



Disertacija rengta 2007–2011 metais Vilniaus universitete.
Moksliniai vadovai:
doc. dr. Darius Jasaitis (Vilniaus universitetas, fiziniai mokslai, chemija - 03 P); (2007–
2010 m.);
prof. habil. dr. Aivaras Kareiva (Vilniaus universitetas, fiziniai mokslai, chemija - 03 P);
(2010–2011 m.).

Disertacija ginama Vilniaus universiteto Chemijos mokslo krypties taryboje:
Pirmininkas:
Prof. habil. dr. Rimantas Ramanauskas (Fizinių ir technologijos mokslų centras,
Chemijos institutas, fiziniai mokslai, chemija - 03 P);
Nariai:
Doc. dr. Ingrida Ancutienė (Kauno technologijos universitetas, fiziniai mokslai,
chemija - 03 P);
Doc. dr. Virgaudas Kubilius (Vilniaus universitetas, fiziniai mokslai, chemija - 03 P);
Prof. habil. dr. Antanas Laukaitis (Vilniaus Gedimino technikos universitetas,
Termoizoliacijos institutas, technologijos mokslai, medžiagų inžinerija - 08 T);
Doc. dr. Jūratė Senvaitienė (P. Gudyno restauravimo centras, fiziniai mokslai, chemija -
03 P).
Oponentai:
Dr. Irma Bogdanovičienė (Vilniaus universitetas, fiziniai mokslai, chemija - 03 P);
Prof. dr. Raimundas Šiaučiūnas (Kauno technologijos universitetas, technologijos
mokslai, chemijos inžinerija - 05 T).

Disertacija bus ginama viešame Chemijos mokslo krypties tarybos posėdyje 2011m.
gruodžio 16 d. 14 val. Vilniaus universiteto Chemijos fakulteto Neorganinės chemijos
auditorijoje.
Adresas: Naugarduko 24, LT-03225 Vilnius, Lietuva. Tel.:2193108. Faksas: 2330987.
Disertacijos santrauka išsiuntinėta 2011 m. lapkričio … d.
Disertaciją galima peržiūrėti Vilniaus universiteto ir FTMC Chemijos instituto
bibliotekose.

1. INTRODUCTION
The development and application of advanced materials is a very important task of
today's information society. Garnet crystal structure compounds because of their specific
physical and chemical properties are widely used in information technology,
manufacturing of solid-state lasers and optical equipments, medical equipments and
many other areas. Therefore, these materials because of their unique properties and
characteristics are of high interest so far.
The yttrium aluminium garnet (Y Al O , YAG) doped with a transition metal or 3 5 12
lanthanide ions, is an important solid-state laser material which is widely used in
fluorescent systems and optical fiber telecommunications systems. In addition, recently
4+ 2+ +the YAG doped with various transition metal ions (Cr , Co and V3 ) has been applied
as passive Q-switch crystals. The YAG oxides are also widely applied as phosphors in
cathode-ray tubes (projection TV settings), electroluminescent and vacuum fluorescent
displays and positron emission tomographs. Besides, the yttrium aluminium garnet is
characterized by a relatively high mechanical strength and high temperature creep
resistance.
The rare earth (RE) garnets are also potential materials which have high mechanical
stability like that of YAG. The rare earth garnets are also used as laser and phosphor
materials. Lutetium aluminium garnet (Lu Al O , LuAG) is widely applied as optical 3 5 12
host material for luminescent powders or single crystals. Rare earth doped LuAG has
found applications in IR lasers, phosphor converted LEDs, X-ray detectors and field
emission displays. The literature highlights that LuAG proves to be a promising host
structure for scintillating materials. So, the synthesis and study of lanthanide aluminium
garnets is relevant and contemporary issue. New, reliable, cost-effective and simple
methods of synthesis should be developed for creating materials which can be used in
modern technologies. The sol–gel technology, due to its apparent advantages of fine
homogeneity, high reactivity of starting materials, low sintering temperature and lower
costs, is a promising method for the preparation of garnet crystal structure. Therefore,
the aim of this study was to synthesize various multiple materials having garnet crystal
structure using an aqueous sol-gel method. Lanthanide aluminium garnets have never
been synthesized using sol-gel method and some of them are not synthesized so far. It
proves that this doctoral thesis is an original study.
5
The aim of the research was to synthesize and study various lanthanide aluminium
garnets using an aqueous sol-gel method. For this reason there were formulated tasks as
follows:
1. For the first time to use the sol–gel method to synthesize lanthanide (Ce, Pr, Nd,
Tb, Dy, Ho, Er, Tm, Yb, Lu) aluminium garnets.
2. To characterize these sol-gel derived garnets using different characterization
techniques.
3. To study the effect of yttrium substitution by neodymium in yttrium aluminium
garnet.
4. To study the effect of yttrium substitution by samarium in yttrium aluminium
garnet.
Statements for defence
The results of the investigations let us defend the most important statements:
1. The sol–gel method is suitable, effective and economical method to synthesize
single-phase polycrystalline Tb Al O (TbAG); Dy Al O (DyAG); Ho Al O 3 5 12 3 5 12 3 5 12
(HoAG); Er Al O (ErAG); Tm Al O (TmAG); Yb Al O (YbAG); 3 5 12 3 5 12 3 5 12
Lu Al O (LuAG) garnet structure compounds, which are characterized by high 3 5 12
level of homogeneity.
2. Ce-Al-O, Pr-Al-O and Nd-Al-O acetate–glycolate gels can not be used for the
synthesis of cerium aluminium garnet Ce Al O , praseodymium aluminium 3 5 12
garnet Pr Al O and neodymium aluminium garnet Nd Al O using the same 3 5 12 3 5 12
synthesis parameters. Instead of presumable lanthanide (Ce, Pr, Nd) aluminium
garnets the samples consisted of cerium oxide (CeO ) and alumina (Al O ) 2 2 3
phases (in cases of cerium), or in cases of neodymium and praseodymium, the
formation of perovskite NdAlO and PrAlO phases took place. 3 3
3. When Nd and Sm are introduced in Y Al O the garnets phases Y Nd Al O3 5 12, 3-x x 5 12
and Y Sm Al O can be synthesized at 1000 °C only when Nd ir Sm 3-x x 5 12
concentrations are suitable. When Nd and Sm concentration is up to 2.5 at %
multiphasic materials are formed. When Nd and Sm concentration is higher,
neodymium and samarium perovskite aluminates are formed instead of garnet
structure compounds.

6
2. EXPERIMENTAL
2.1. Materials and reagents
For the sol-gel synthesis stoichiometric amounts of Y O , [NH ] [Ce(NO ) ], 2 3 4 2 3 6
Pr O , Nd O , Sm O , Tb O , Dy O , Ho O , Er O , Tm O , Yb O , Lu O , 6 11 2 3 2 3 4 7 2 3 2 3 2 3 2 3 2 3 2 3
Al(NO ) ·9H O as starting compounds, ethane-1,2-diol (HOCH CH OH) as 3 3 2 2 2
complexing agent, all of them analytical grade, were used.
2.2 Methods of synthesis
Nd, Dy, Ho, Er, Tm, Yb and Lu acetates were prepared by dissolving the
-1 corresponding lanthanide oxides in 2×10 M acetic acid (100 ml). Clear solutions were
0obtained after stirring at 60–65 C for 10 h in beakers covered with a watch-glass.
However, terbium and praseodymium oxide were found not soluble in acetic acid.
Therefore, these oxides were dissolved in 65% nitric acid at the same temperature.
[NH ] [Ce(NO ) ] was dissolved in 100 ml of distilled water. Then, aqueous solution of 4 2 3 6
aluminium nitrate nonahydrate (25 ml) was added to above solutions. The resulting
0mixtures were stirred at 60-65 C for 1 h, followed by dropwice addition of ethane-1,2-
diol (2 ml) upon vigorous stirring. The resulting sols were mixed at the same temperature
0for another 1 h and then concentrated by slow solvent evaporation at 60-70 C until they
0turned into transparent gels. The gels were dried in an oven at 105 C for 10 h. The
0resulting gel powders were ground in an agate mortar and heated in air at 800 C for 4 h
0 -1by slow temperature elevation (~ 3–4 C min ). After grinding in an agate mortar, the
0powders were further sintered in air at different temperatures (800–1200 C) for 10 h.
Yttrium-neodymium aluminium garnet (Y Nd Al O , YNdAG) (x = 0.1, 0.25, 3-x x 5 12
0.35, 0.5, 0.6, 0.7, 0.8, 1.5, 2, 2.5, 3) and yttrium-samarium aluminium garnet
(Y Sm Al O , YSmAG) (x = 0.1, 0.15, 0.25, 0.5, 0.75, 1, 1.5, 2, 2.5, 3) samples were 3-x x 5 12
synthesized by an aqueous sol-gel method. Y, Nd and Sm acetates were prepared by
-1 dissolving the corresponding lanthanide oxides in 2×10 M acetic acid (100 ml). Clear
0solutions were obtained after stirring at 60–65 C for 10 h in beakers covered with a
watch-glass. Then, aqueous solution of aluminium nitrate nonahydrate (25 ml) was
added to above solution. Neodymium acetate or samarium acetate was added to initial
0mixture. The resulting mixtures were stirred at 60-65 C for 1 h, followed by dropwice
addition of ethane-1,2-diol (2 ml) upon vigorous stirring. The resulting sols were mixed
at the same temperature for another 1 h and then concentrated by slow solvent
7
0evaporation at 60-70 C until they turned into transparent gels. The gels were dried in an
0oven at 105 C for 10 h. The resulting gel powders were ground in an agate mortar and
0 0 -1heated in air at 800 C for 4 h by slow temperature elevation (~ 3–4 C min ). After
0grinding in an agate mortar, the powders were further sintered in air at 1000 C for 10 h.
2.3. Characterization and techniques
The XRD studies were performed on a Philips Xpert diffractometer (CuKα1
radiation;  = 1.5406 A ˚) (for Ce Al O , Pr Al O , Nd Al O , Tb Al O , Dy Al O 3 5 12 3 5 12 3 5 12 3 5 12 3 5 12
and Er Al O ), Bruker AXE D8 Focus Diffractometer, LynxEye detector (CuKα 3 5 12
radiation;  = 1.5406 Å) (for Ho Al O , Tm Al O , Yb Al O and Lu Al O ). IR 3 5 12 3 5 12 3 5 12 3 5 12
spectra were recorded with Perkin–Elmer FT-IR Spektrum BX II or Bruker EQUINOX
55/S/NIR FTIR spectrometers. Scanning electron microscopes CAM SCAN S4 (for
Ce Al O , Pr Al O , Nd Al O , Tb Al O , Dy Al O and Er Al O ), FE-SEM Zeiss 3 5 12 3 5 12 3 5 12 3 5 12 3 5 12 3 5 12
Ultra 55, In-Lens detector (for Ho Al O , Tm Al O , Yb Al O and Lu Al O ) were 3 5 12 3 5 12 3 5 12 3 5 12
used to study the morphology and microstructure of the ceramic samples.

3. RESULTS AND DISCUSSION
3.1. Sol gel synthesis and characterization of lanthanide (Tb, Dy, Ho, Er, Tm, Yb,
Lu) aluminium garnets
The synthesis of lanthanide (Tb, Dy, Ho, Er, Tm, Yb, Lu) aluminium garnets via
simple aqueous sol–gel method has been suggested. For the first time Tb Al O , 3 5 12
Dy Al O , Ho Al O , Er Al O , Tm Al O , Yb Al O and Lu Al O compounds 3 5 12 3 5 12 3 5 12 3 5 12 3 5 12 3 5 12
were synthesized using sol-gel method.

3.1.1 XRD characterization of lanthanide (Tb, Dy, Ho, Er, Tm, Yb, Lu) aluminium
garnets

In the first part, the Tb-Al-O, Dy-Al-O, Ho–Al–O, Er-Al-O, Tm–Al–O,
0Yb–Al–O and Lu–Al–O precursor gels were calcined at 800 C for 5 h and finally
0annealed at 1000 C for 10 h. The X-ray diffraction patterns of the Tb–Al–O, Dy–Al–O
0and Er–Al–O precursor gels annealed at 1000 C are shown in Fig. 1. The XRD results
0presented in Fig. 1a revealed that Tb–Al–O ceramics obtained at 1000 C consists of one
8
crystalline phase: terbium aluminium garnet (Tb Al O ). The obtained XRD pattern is 3 5 12
in a good agreement with the reference data for Tb Al O (PDF [17–735]). 3 5 12




Ho Al O (c)
3 5 12



Dy Al O (b)3 5 12


Tb Al O (a)3 5 12


20 30 40 50 60 70 80

    

Fig. 1. XRD patterns of Tb Al O (a), Dy Al O (b) and Ho Al O (c) ceramic 3 5 12 3 5 12 3 5 12
0powders, synthesized by sol–gel method and annealed at 1000 C for 10 h.

Fig. 1b reveals that only one dysprosium aluminium garnet Dy Al O phase (ICSD 3 5 12
0[00-022-1093]) was also obtained after calcination of precursors at 1000 C. In the case
of the holmium aluminium system, the analogous results were obtained. In Fig. 1c the
X-ray diffraction pattern of the final holmium aluminium ceramic sample annealed at
01000 C is presented. The XRD pattern proves the formation of the cubic holmium
aluminium garnet (Ho Al O ). Evidently, the obtained XRD pattern is in good 3 5 12
agreement with the reference data for Ho Al O (ICSD [00-076-0112]). 3 5 12
The X-ray diffraction patterns of the Er–Al–O, Tm–Al–O, Yb-Al-O and Lu–Al–O
0precursor gels annealed at 1000 C are shown in Fig. 2. The XRD results presented in
0Fig. 2a revealed that ceramics obtained at 1000 C consists of one crystalline phase of
erbium aluminium garnet (Er Al O ). The obtained XRD pattern is in a good agreement 3 5 12
with the reference data for Er Al O (PDF [32–12]). Fig. 2b reveals that only one 3 5 12
thulium aluminium garnet Tm Al O phase was obtained after calcinations of precursors 3 5 12
9

Relative intensity (a. u.)
211
220
321
400
420
332
422
431
521
440
620
631
444
640
552
642
651
800
0at 1000 C (ICSD [04-001-9712]). Fig. 2c is the X-ray diffraction pattern of the final
0Yb–Al–O ceramic powders annealed at 1000 C. Evidently, the obtained XRD pattern is
in good agreement with the reference data for Yb Al O (ICSD [00-023-1476]). Fig. 2d 3 5 12
shows XRD pattern of monophasic Lu Al O phase. All indexed lines have been 3 5 12
assigned to the pure polycrystalline Lu Al O phase (ICSD [04-001-9996]). 3 5 12





Lu Al O (d)3 5 12


Yb Al O (c)3 5 12


Tm Al O (b)
3 5 12


Er Al O (a) 3 5 12


20 40 60 80
    

Fig. 2. XRD patterns of Er Al O (a), Tm Al O (b), Yb Al O (c) and Lu Al O (c) 3 5 12 3 5 12 3 5 12 3 5 12
0ceramic powders, synthesized by sol–gel method and annealed at 1000 C for 10 h.

0 The solid state reactions expressed by Eqs. (3.1) proceed completely at 1000 C,
which is rather low temperature for such type of ceramics.
1.5 Ln O + 2.5 Al O → Ln Al O (Ln = Tb, Dy, Ho, Er, Tm, Yb, Lu) (3.1) 2 3 2 3 3 5 12
Therefore, the optimum temperature for the formation of Tb Al O , Dy Al O , 3 5 12 3 5 12
0Ho Al O , Er Al O , Tm Al O , Yb Al O and Lu Al O garnets is 1000 C. 3 5 12 3 5 12 3 5 12 3 5 12 3 5 12

3.1.2 IR characterization of lanthanide (Tb, Dy, Ho, Er, Tm, Yb, Lu) aluminium
garnets

10

Relative intensity (a. u.)
211
220
321
400
420
332
422
521
440
611
444
640
552
642
800
842