synthesis and characterization of yttrium-aluminum-iron and yttrium-cerium-iron citric complexes

JOURNAL OF RARE EARTHS, Vol. 26, No. 3, Jun. 2008, p. 307

Corresponding author: D. Todorovsky (E-mail: [email protected]; Tel.: +359-2-8161-322)

Synthesis and characterization of yttrium-aluminum-iron and yttrium-cerium-iron citric complexes

N. Petrova1, D. Todorovsky1, I. Mitov2, G. Tyuliev2 (1. Faculty of Chemistry, University of Sofia, 1, J. Bourchier Blvd., Sofia 1164, Bulgaria; 2. Institute of Catalysis, Bulgarian Academy of Sciences, Acad. G. Bonchev Str., bl. 11, Sofia 1113, Bulgaria) Received 16 August 2007; revised 10 September 2007

Abstract: Fe-, Y-Fe-Al- and Y-Ce-Fe- citrates were synthesized in ethylene glycol (EG) medium under conditions similar to those used in the polymerized complex method. Their elemental composition, IR, 13C and 1H NMR, X-ray photoelectron and Mössbauer spectra were studied, and formulae describing their composition were proposed. The complexes contained EG bonded as adduct and ester with citric acid ligand and did not contain ligands with deprotonated alcoholic groups. The complexes consisted of agglomerated spheres, 0.7−3 µm in di-ameter. The local composition of the products was established by energy dispersive X-ray microanalysis. The comparison of the number of the ligands, their average electrical charge and the esterification degree of mono-, di- and trimetallic complexes proved the mixed-metal na-ture of the species studied. The thermal decomposition of the complexes was studied and a general scheme of the processes taking place was proposed. Highly crystalline, phase homogeneous Y3Fe4AlO12 was produced after heating the respective complex at 1000 °C. Ce-doped yt-trium-iron garnet, similarly prepared, contained traces of CeO2.

Keywords: garnets; polymerized complex method; Мössbauer spectroscopy; thermal analysis; NMR-spectroscopy; rare earths

Owing to its interesting magneto-optical properties, Ce-doped Y3Fe5O12 (YIG:Ce) is widely applied as mono- and polycrystalline material and as thin layers. Along with the solid state reaction between the respective oxides, the coprecipitation of carbonates, oxalates and hydroxides is also used for its preparation[1]. The same method is applied for the production of Al-doped garnets of the Y3Fe5-xAlxO12

(x=1–5) type[2]. A gel formed by dissolving metal nitrates (used as a source of the respective metals) in ethylene glycol (EG) is used for the preparation of Cr-doped yttrium iron garnets in[3]. Fine-powdered YIG is obtained by an alkoxide sol-gel process[4]. Ultra finely dispersed doped rare earth garnets are fabricated by the so-called citric method igniting the gel obtained by evaporation of aqueous citric acid (CA) solution of the metal cations at 900 °C[5]. The first successful deposition of YIG:Ce films is reported in Ref.[6]. EG solu-tion of Y-Fe citric complex is used as starting material for spray-pyrolysis deposition of uniform YIG films[7]; forma-tion of mixed-metal citric complexes was proven in the sys-tem Y3+-Fe3+-CA-EG under the conditions applied for preparation of the starting solution[8]. The mixing of the metals at an atomic level enhances the formation of highly crystalline, stoichiometric, phase homogeneous films with rather good magnetic properties[7]. This approach is based on the well-known Pechini's reaction developed as the widely

used polymerized complex method (PCM). The knowledge of the chemistry of complexation and the thermochemical processes involved in the PCM application is of significant importance for the prediction of its effectiveness in different systems and for its optimal implementation. In a number of articles[8–18], the complexes formed in different systems un-der the conditions of PCM application were synthesized, isolated and their composition, spectral characteristics and thermochemical behavior were studied. In some of the stud-ied bimetallic systems, the formation of mixed metal com-plexes was found out[19].

Although the PCM is used for the production of trimetal-lic oxides[20–22], the published data on the complexation processes taking place in such systems are limited. In the present paper the citrates formed in the trimetallic Y-Al-Fe-CA-EG and Y-Ce-Fe-CA-EG systems were stud-ied as potential precursors for Al- or Ce-doped YIG. The study was promoted by the investigations of the individual Y-[10]; Y-Fe-[8]; Al-, Y-Al-[17] and Ce-[18] citrates that were already performed.

1 Experimental

1.1 Complexes preparation

mailto:[email protected];

308 JOURNAL OF RARE EARTHS, Vol. 26, No. 3, Jun. 2008

Y(NO3)3·6H2O, Fe(NO3)3·9H2O, Al(NO3)3·9H2O, Ce(NO3)3·6H2O, citric acid monohydrate (CA), EG and acetone, all of p.a. grade, were used for the complexes syn-thesis and isolation. The precise content of the metals in the used crystallohydrates was determined by complexometry (Y, Al, Fe) and redoxymetry (for Ce, after oxidation to Ce4+).

For the preparation of the complexes, a weighed amount of CA was dissolved in a measured volume of EG under continuous stirring and heated to 40 °C. The weighed amount(s) of the metal salt(s) was (were) added to the ob-tained transparent solution so as the mole ratios (Table 1) ensuring the equal amount of CA and EG per a unity elec-trical charge of the ions to be adjusted. After dissolution, the solutions were heated under continuous stirring as shown in Table 1. The complexes formed were isolated by the addi-tion of acetone in volume 10 times larger than the solution volume, following an earlier applied procedure[9]. The pre-cipitate formed was soaked in a fresh portion of acetone for 24 h, filtrated, dried at room temperature and stored in tightly closed vessels. Previously studied Y-, Al-, Y-Al- and Y-Fe-citrates have been produced following the same method[8,10,16]. The used metal(s), CA:EG mole ratios and the heating temperatures were similar to the ones commonly used in PCM.

Table 1 Complexes synthesis conditions

System Mole ratio Temperature, oC/ time of heating, min

Sample symbol

Fe(III)-CA-EG 1:6:24 100/10 FeCit

Y-Fe(III)-Al-CA-EG 1:1.33:0.33:15:75 100/30 YFeAlCit

Y-Ce(III)-Fe(III)-CA-EG 2.5:0.5:5:34:137 80/30 YCeFeCit

1.2 Powdered materials preparation

The final materials were obtained by two methods: (1) Heating the isolated complexes under defined condi-

tions; (2) Heating the EG-citric solution at 300 oC for 4 h fol-

lowed by heating the polyester resin formed at 550 °C for 30 min and at 1000 °C for 2–4 h. Obviously, this procedure was very similar to the one used in PCM.

1.3 Analysis

The relative content of H, C and N in the complexes was determined by the common organic analysis methods.

To determine the metals, the complexes were mineralized by very careful step-wise treatment with conc. H2SO4 and H2O2 (30%) at approx. 300 °C. In the obtained clear solu-tions:

(1) Fe in FeCit was determined complexo-metrically (at

pH=6 and xylenolorange as indicator); (2) Fe in YFeAlCit was measured also by titration with

complexon III at pH=2, temperature 60–70 °C and sul-fosalicilic acid as indicator. After bonding of Fe3+ with the complexon, the rested sulfosalicilic acid and the added ace-tylacetone mask the Al3+, then Y3+ was titrated with com-plexon III at pH=6 and xylenol orange as indicator. In other aliquot Al3++Fe3+ were determined by reverse titration with Zn2+ solution at the same pH and indicator;

(3) Fe in YCeFeCit was determined by the above- de-scribed procedure. In aliquot, the cerium was oxidized at boiling the sulfuric acid solution with (NH4)2S2O8 and AgNO3 as catalyst. The so-obtained Ce4+ was determined redoxymetrically with (NH4)2Fe(SO4)2 solution using pheroin as indicator. The sum of all the metals was deter-mined by reverse complexometric titration with La(III)-so-lution at pH=6 and xylenol orange as indicator.

Atomic absorption spectrometry was also used for verifi-cation of the results concerning the Fe-content. Additional data were also received by energy dispersive X-ray micro-analysis and X-ray photoelectron spectroscopy.

IR spectra of the complexes were recorded in nujol mulls or in KBr pellets with Specord 75 (Carl Zeis, Germany) spectrophotometer. 13C and 1H NMR spectra were taken in D2O solution with a spectrometer Bruker DRX 250 MHz. X-ray powder diffractometry was performed by Siemens diffractometer (40 kV, 40 mA, Cu Kα and 0.3° 2θ-step/17 s). Mössbauer spectra were taken by the electromechanical spectrometer (Wissenschaftliche Elektronic GmbH, Ger-many) at room temperature with 57Co/Cr radioactive source and α-Fe as standard. The morphology and local composi-tion of the complexes were studied by SEM (JEOL JSM 35CF scanning electron microscope) and energy dispersive X-ray microanalysis (Tractor Northern TN-2000). X-ray photoelectron spectroscopy was done in a UHV camera of ESCALAB-MkII (VG Scientific) at 10-5 Pa with MgKα-ra-diation by the C1s, Fe2p, O1s, Al2p, Ce3d and Y3d photo-electron lines. The C2s peak of CH2 at 285 eV was used for spectra calibration. DTA, TG and DTG curves were re-corded by Paulik-Paulik-Erdey (MOM, Hungary) deriva-tograph. Approximately 0.2 g of the sample was heated in a synthetic corundum crucible at a rate of 10 °C/min.

2 Results and discussion

2.1 Composition and spectral characteristics of the studied complexes

The content of H, C, N, metals and H2O (the latter deter-mined by the thermogravimetric analysis) is shown in Ta-ble 2. These data along with the reported below spectral data

N.Petrova et al., Synthesis and characterization of yttrium-aluminum-iron and yttrium-cerium-iron citric complexes 309

Table 2 Content (%) of H, C, N, metals and H2O in the studied complexes (experimentally founded, in brackets-calculated

according to the formulae shown in Table 3) Sample symbol* H C N Fe Y Al Ce H2O

FeCit 5.24 (5.80)

34.85 (34.87)

0 (0)

6.67 (7.51) - - - 8.4

(8.5)

YFeAlCit 4.41 (4.40)

30.80 (30.95)

0.7 (0.70)

5.02 (5.85)

6.15 (7.00)

0.65 (0.70) - 7.3

(7.1)

YCeFeCit 4.52 (4.46)

29.73 (29.24)

0.63 (0.79)

5.43 (6.94)

6.82 (6.28) - 1.28

(1.58) 9.3

(10.2)

* For the symbols meaning see Table 1

Table 3 Supposed formulae of the complexes Sample symbol1) Supposed formula2) Molar mass

FeCit Fe(HCitROH2-)[HCit(ROH)2-]. 1.8HOROH.3.5H2O 744.0

YFeAlCit YFe1.33Al0.33(HCitROH2-)3.64(NO3-)0.7

.1.8HOROH.5H2O 1269.6

YCeFeCit 3) YCe0.16Fe1.76(HCitROH2-)4.03(NO3-)0.86

.HOROH.8H2O 1416.0

1) See also Table 1; 2) HCit: CH2COO-C(OH)COO-CH2COO, R=(CH2)2; 3) Supposing Ce is present as Ce4+

Fig.1 IR spectra (4000–400 cm–1, KBr pellets) of FeCit (1), YFe-

AlCit (2) and YCeFeCit (3) lead to the hypothetical formulae (Table 3) of the studied complexes.

The presence of H2O in the isolated compounds is proven by the broad band at –3450 cm–1 in the IR spectra (Fig.1). A well-defined shoulder at 1040 cm–1 in the IR spectra (Fig.1) belonging to ν (C-OH) of EG as well as the peaks at 65 ppm

in 13C NMR spectra (Fig.2) and at –3.5 ppm in the 1H NMR spectra (Fig.3) are associated[9] with CH2 groups of EG bonded as adduct.

The resonance signals around 62 ppm and 69 ppm (Fig.2) and around 3.7 and 4.1 ppm (Fig.3) assigned[10] to OCH2 and HOCH2 groups of EG confirm the presence of esters. How-ever, due to very low solubility of the complexes in D2O, the quality of the NMR and especially of the 1H-spectra is rather low. For this reason, it is not possible to use the intensity ra-tios of the proton signals of the CH2 groups of EG and of CA (at 2.8–3.2 ppm) for the determination of the degree of the ligand esterification with EG and of the relative content of the adduct-bonded EG as it is done in Refs.[9,12,14,17]. This makes the qualitatively correct formulae given in Table 3 only tentative from a quantitative point of view. They are derived by analogy with much stronger proven formulae of similar complexes[9,12,14,17] and represent the simplest description of the elemental composition of the precipitates.

The complexation processes are confirmed by the absorp-tion bands at –1620 cm–1 /(νas(COO–)/ and around 1440 cm–1

/(νs(COO–)/ in the IR spectra (Fig.1). The strong peak at

Fig.2 13C NMR spectra of FeCit (a), YFeAlCit (b) and YFeCeCit (c)


Fig.3 1H NMR spectra of FeCit (a) and YFeAlCit (b)

~1390 cm–1 is caused by the presence of NO3

– in the sam-ples[23].

No signal at –90 ppm in the 13C NMR spectra (Fig.2) is observed. This signal is because of the presence of central C- atom of the CA bonded with deprotonated OH group[24]. Such a signal was found [18] in the spectrum of Ce citrate prepared by the same way as the complexes studied in this article.

Signals in the region 175–181 ppm (Fig.3) in the 13C NMR spectra are associated with the COO– groups. The Mössbauer spectra of the studied complexes, as well as those of Y-Fe citrate synthesized by the same way are shown in Fig.4. The experimental spectra are interpreted using two models, namely, (1) with one quadrupole doublet and (2) as a superposition of two doublet lines. Better con-formity between the theoretical and experimental functions was reached by the first model for FeCit and by the second one for all of the other citrates. The results indicate that all of the studied samples are paramagnetic and the iron is pre-sented as Fe(III) only. The value of the isomeric shift (IS) shows octahedral coordination of the Fe in FeCit (IS=0.427 mm/s). Two types of ion are seen in the polymet-allic compounds, namely, with octahedral coordination (doublet with higher intensity IS1=0.427 mm/s, quadrupole splitting QS1=0.596 mm/s) and with close to tetrahedral co-ordination (low intensity doublet, IS2=0.213–0.314 mm/s, QS2=0.06 mm/s). According to the relative weight of the doublet lines, the ratio octa/tetra is 65/35 for YCeFeCit and 80/20 for YFeAlCit. The differences between the deter-mined parameters of the hyperfine interactions (isomer shift and quadrupole splitting) between FeCit and the polymetal-lic samples show that the introduction of Y and Ce leads to changes in the ligand field around Fe-ions, that is, the char-acteristics of the chemical bond and the electrical charge symmetry around the iron nucleus are slightly changed. The

broadening of the spectral lines (FWHM1=0.539 mm/s, FWHM2=1.2−1.7 mm/s) suggests that the studied samples consist of species with similar but not just the same ligand environment which is characteristic for the amorphous sub-stances.

The small differences in the binding energy of the iron found by X-ray photoelectron spectroscopy (Fig.5, Table 4)

Fig.4 Mössbauer spectra of the studied complexes interpreted by

the models of one quadrupole doublet (FeCit) and as super-position of two doublet lines (all other complexes)


confirms the above mentioned results from the Mössbauer spectroscopy concerning the influence of the Al and Ce on the Fe coordination state. The mole ratio Y:Fe:Al= 1:1.35:0.4 determined from the XPS results is about the one accepted in the proposed formula (Table 3). The spectrum profile in the Fe2p region suggests the presence of Fe(II) on both the complexes’ surfaces in contradistinction from their volume. The reasons for the reduction process taking place only on the surface of the samples are not clear so far. Any-way, during the following thermal treatment oxidation process proceeds and Fe(III) oxidation state is being recov-ered (see below the diffractograms of the products resulting from the complexes thermal decomposition).

2.2 Complexes morphology

The studied polymetallic complexes consist of agglomer-ated spheres 2–3 µm in diameter for YFeAlCit and 0.7–1 µm for YCeFeCit. The agglomeration is stronger ex-

pressed in the case of YCeFeCit (Fig.6). Blocks of irregular form are also present in YFeAlCit. The X-ray microanalysis shows some differences between the compositions of the spheres and blocks. The results obtained from different points vary in relatively wide limits (the relative standard deviations of the contents of Fe and Y are 6% and 13%, re-spectively), so it is not possible to draw reliable conclusions.

2.3 Thermal decomposition of the complexes

DTA, DTG and TG curves for the studied complexes are shown in Fig.7. The thermal decomposition of Y[10], Ce[18], Y-Fe[12], Al and Y-Al [17] citrates have been studied, and the identification of some of the intermediates was done. It seems that the thermochemical behavior of the individual Fe and polymetallic compounds studied follows the general scheme of the processes taking place during the thermal de-composition of the above-mentioned substances.

Fig.5 Photoelectron spectra of YFeAlCit (a) and YCeFeCit (b)

Fig.6 SEM images of YFeAlCit (a) and YCeFeCit (b)

Table 4 Bonding energies (eV) in the polymetallic complexes Sample symbol * C1s O1s Y3d3/2 Y3d5/2 Fe2p3/2 Fe2p1/2 Al2p Ce3d

YFeAlCit 285.0, 286.3, 288.6 531.85 158.3 160.0 709.7 722.9 74.1 -

YCeFeCit 285.0, 286.2, 288.7 531.85 158.5 160.1 710.2 723.6 - 855.7

* For the symbols meaning see Table 1, 2


Fig.7 DTA, DTG and TG curves of YFeAlCit (a) and YCeFeCit (b)

The complexes are stable up to 40–50 oC. The dehydra-

tion takes place up to 150 oC (YCeFeCit) and up to 180 oC (YFeAlCit). In some cases (FeCit, YFeAlCit), the DTG curves show that the process proceeds in two stages. Ap-proximately 2/3 of the present water (probably adsorbed) is released up to 125–140 oC. The remaining water (probably coordinated) is evolved up to 165–180 oC. The experimen-tally founded mass loss during the latter stage for all of the studied samples is in a very good agreement with the ex-pected values according to the formulae shown in Table 3.

The dehydration continues as intramolecular process, quite common for citric complexes, with formation of C=C bond and transformation of the citrate to aconitate. This is confirmed by the appearance of the band at 937 cm–1 in the IR spectra of the intermediates taken at 180–210 oC[13,14].

In all the studied samples, the above-mentioned process is overlapped by the evolution of adduct (bonded EG), de-esterification and decarboxylation of the formed COOH- groups (up to 245–350 oC for the different compounds). The band at 1040 cm–1 in the IR spectra /ν(C-OH) from the EG/ no longer exists. At this stage, the mass loss of YCeFeCit is 34.4% (found) and 34.8% (calculated according to the pro-posed formulae). For FeCit and YFeAlCit, the decarboxila-tion takes place at 300 and 350 oC, respectively and the IR band at 1720 cm–1 disappears. Destruction of the organic skeleton takes place above 245–285 oC up to 415–460 oC accompanied by a mass loss of YCeFeCit which is found to be about 26.8% (25.1% cal-culated). The final product formed is mixed with the re-maining carbon. The latter burns in a few stages with an exothermic effect, at about 600–630 oC. The mass loss (1.4%–1.9 %) above this temperature is caused by the re-lease of small amounts of CO2 adsorbed on the final prod-ucts.

The weak exoeffects at 765 oC (YFeAlCit) and at 770 and 835 oC might be assigned to the final product(s) crystalliza-

tion. A similar effect is evidenced by the DTA curve of Ce citrate decomposition to CeO2

[18] at 840 oC and by the same curve of Y-Al-citrate with Y/Al mole ratio 1 but at 900 oC[17].

X-ray diffractogram of the final product after the heating of YFeAlCit is shown in Fig.8. The interplanar distances are identical (within the limits of the method error) with those of Y3Fe4AlO12 (JCPDS 44-0228).

The XRD patterns of the final products obtained after heating at 1000 oC for 2.5 h of the isolated YCeFeCit and of the polyester resin prepared by the common PCM from the same solution (subsection 1.2) are shown in Fig.9. The data for the interplanar distances and the relative intensity are compared with JCPDS data for Y3Fe5O12, YFeO3, Fe2O3 and CeO2 materials. The products produced by both the proce-dures are not phase homogeneous. A heating of the complex leads to crystallization of a product with structure practically identical with that of the cubic Y3Fe5O12 but the sample also contains a small amount of CeO2. The interplanar distances of the main phase are very close to the one of c-Y3Fe5O12

Fig.8 X-ray diffractogram of Y3Fe4AlO12 produced by heating of

YFeAlCit for 1 h at 450 oC and for 2.5 h at 1000 oC; Miller indices are shown


Fig.9 X-ray diffractogram of the product obtained from heating of

YCeFiCit for 1 h at 450 °C and for 2.5 h at 1000 °C (1, Miller indices of c-Y3Fe5O12 are shown) and of the polyester resin received by heating of the initial solution for 4 h at 300 °C, 0.5 h at 550 °C and 3 h at 1000 °C (2, Miller indices of the orthorombic YFeO3 are shown); o - cubic CeO2, * - Fe2O3 (hematite)

(JCPDS 43-0507). The substitution of Y3+ (ionic radii 104 pm) with Ce3+ (115 pm) leads to a certain increase in the interplanar distances. The absence of such an increase could be due to the relatively small quantity of Ce intro-duced in the YIG cell.

The product obtained from the polyester resin (Fig.9) is even of further less phase homogeneity, namely, it contains orthorombic YAlO3, Fe2O3 (hematite) and CeO2. Traces of CeO2 have also been found by Mančić et al.[25] in the pro-duction of Ce-doped yttrium-aluminum garnet from nitrates aerosol.

2.4 On the nature of the studied complexes

Some main characteristics of the composition of the stud-ied mono- and polymetalic citrates according to the pro-posed formulae are listed in Table 5. The mixed-metal na-ture of YAl[17] and Y3Fe5 citrates[8] has been proven. The data in Table 5 show that trimetallic complexes are not a

mixture of individual complexes. Indeed, the number of ligands per metallic atom is much lower than in the case of the individual (and in the bimetallic) complexes and, respec-tively, the average ligand electrical charge is higher, the es-terification degree, as well as the values of the other pa-rameters are not means of the respective values of the indi-vidual complexes. From this point of view, the studied trimetallic complexes cannot be described as mixtures of Y-Fe and Al, respectively Ce complexes. The Mössbauer and XPS data also confirm the influence of the substitutes on the Fe-ligand field and bonding. The derived formulae, as well as the broadening of the Mössbauer signals clearly show that the isolated precipitates are mixtures of similar but unidentical species. The data for the analogous com-plexes[10,18] show that the differences are mainly between the numbers of deprotonated COOH groups, degree of esterifi-cation and probably between the relative content of ad-duct-bonded EG.

Following the Mössbauer data, it has to be supposed that the studied systems are more complicated. The Y-Fe system and the trimetallic systems based on it contain species with different types of coordination.

It is seen that Y, Al and Fe are bonded in the isolated pre-cipitate in the ratio equal to the one in the initial solution. Some deviation in the composition of the isolated precipitate compared with that of the initial solution is observed in Y-Ce-Fe-containing precipitate. Similar deviation is found in Y-Fe (mole ratio 1) citrates and tartrates[17,26].

3 Conclusion

The reported data suggested that PCM was a convenient method for the production of Al-doped YIG of the type Y3Fe4AlO12. The formed complex(es), most probably of a mixed-metal nature, reproduce(d) the metals mole ratio ad-justed in the initial solution. Their heating at 1000 oC for 2.5 h led to obtaining of highly crystalline, stoichiometric and phase-homogeneous product.

Table 5 Main characteristics of the isolated compounds

Mole ratios7)

ROH/L R/L (ROH+R)/L HOROH/L H2O/L Sample symbol* L1 2) ZL 3)

LH/L 4) L-/L 5) F 6) C 6) F C F C F C F C

YCit [10] 1.8 1.67 0 0 0.89 0.89 0.26 0.22 1.15 1.11 0.09 0.06 1,40 1.67 AlCit [17] 2.1 1.43 0.55 0 1.00 0.87 - - 1.00 0.87 0.17 0.15 - 1.43 FeCit 2.00 1.50 0 0 - 1.50 - - 1.50 2.39 0.96 0.90 - 1.75 YAlCit [17] 1.6 1.88 0 0 1.23 1.28 - - 1.23 1.28 0.53 0.54 - 1.43 YFeCit [8] 2.06 1.45 0 0 0.58 0.58 0 0 0.58 0.58 0.15 0.15 - 1.82 YFeAlCit 1.37 2.00 0 0 - 1.0 - - - 1.0 0.48 0.48 - 1.37 YCeFeCit 1.39 2.00 0 0 - 1.0 - - - 1.0 0.23 0.23 - 1.97

* For the symbols meaning see Table 1, 2; 2) number of the ligands per one metal atom; 3) ZL: average charge of the citric ligand; 4) LH: number of the ligands with protonated СООН group; 5) L-: number of the ligands with deprotonated OH group; 6) F: experimentally found; C: calculated according the formulae proposed in Table 3; 7) R=(CH2)2; L: total number of ligands


The content of the metals in the isolated precipitate con-

taining Y-Ce-Fe deviated from the metals ratio in the initial solution. The application of the polymerized complex method to the Y-Ce-Fe system led to obtaining of a not phase-homogeneous final product. Heating of the complex isolated from the initial solution led to a much better result but again the final product was not phase-homogeneous; traces of CeO2 are detected.

In general, the thermal decomposition of the studied citrates followed the scheme proposed for other similar complexes.

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synthesis and characterization of yttrium-aluminum-iron and yttrium-cerium-iron citric complexes

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