Microcrystalline phase transformation from ZrF4·HF·2H2O to ZrO2 through the intermediate phases ZrF4·3H2O, ZrF4·H2O, Zr2OF6·H2O and ZrF4

Chemical Physics Letters 612 (2014) 8–13

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Microcrystalline phase transformation from ZrF4 ·HF·2H2 O to ZrO2 through the intermediate phases ZrF4 ·3H2 O, ZrF4 ·H2 O, Zr2 OF6 ·H2 O and ZrF4 C.C. Dey Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700064, India

a r t i c l e

i n f o

Article history: Received 8 May 2014 Received in revised form 30 June 2014 In final form 28 July 2014 Available online 6 August 2014

a b s t r a c t The behavior of hydrated zirconium fluoride has been studied by perturbed angular correlation spectroscopy. It is found that the crystalline compound ZrF4 ·HF·2H2 O, formed initially by drying solution of Zr metal in concentrated HF, transforms spontaneously to ZrF4 ·3H2 O. This trihydrated compound dehydrates to ZrF4 through the intermediate monohydrates ZrF4 ·H2 O and Zr2 OF6 ·H2 O. The compound ZrF4 finally transforms to ZrO2 at ∼343 K. Different crystalline phases of ZrF4 ·HF·2H2 O, ZrF4 ·3H2 O, ZrF4 ·H2 O, Zr2 OF6 ·H2 O, ZrF4 and ZrO2 have been identified and characterized by PAC spectroscopy. From previous PAC measurements, the intermediate ZrF4 ·H2 O and Zr2 OF6 ·H2 O were not observed and the dehydration from ZrF4 ·3H2 O to ZrF4 was found to be routed directly. Present measurements by PAC exhibits dissimilar crystal structures for ZrF4 ·3H2 O and ZrF4 ·H2 O unlike the crystal structures found in hafnium analogous compounds. © 2014 Elsevier B.V. All rights reserved.

1. Introduction The crystal structures of iso-formulae compounds of Hf and Zr in most cases are found to be the same and present very similar physical and chemical properties. As a result, from perturbed angular correlation spectroscopy, similar PAC spectra and nearly equal PAC parameters like quadrupole frequency, asymmetry parameter in the compounds of HfO2 /ZrO2 [1], HfF4 /ZrF4 [2,3], Rb2 HfF6 /Rb2 ZrF6 [4] and similarly for many others were observed [5]. But, there are very few cases where the iso-formulae compounds of Hf and Zr do not have the same crystal structure. One such example is the HfF4 ·3H2 O system. Both from X-ray diffraction [6] and perturbed angular correlation studies [7], the crystal structures of ZrF4 ·3H2 O and HfF4 ·3H2 O were found to be different. It was found that ZrF4 ·3H2 O crystallizes in the triclinic system [8], forming dimers, and the H2 O molecules are directly bound to the central atom. But, HfF4 ·3H2 O, which crystallizes in the monoclinic system [9], exhibits a chain structure. For this compound, one of the H2 O molecules is not coordinated to the Hf atom, but is held between chain-like complexes by hydrogen bonds. In fact, from previous X-ray diffraction measurements [6], it was found that neither HfF4 ·3H2 O nor HfF4 ·H2 O are isostructural with the

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analogous zirconium compounds. Furthermore, while the compounds HfF4 ·3H2 O and HfF4 ·H2 O were found to have same crystal structures [6] with the two water molecules of HfF4 ·3H2 O are structurally unimportant, no such similarity in structural behaviors were found for ZrF4 ·3H2 O and ZrF4 ·H2 O [6] systems. Similar crystal structures for HfF4 ·3H2 O and HfF4 ·H2 O were observed also from PAC studies [2] through the measured values of quadrupole frequencies (ωQ ) and asymmetry parameters () which produced nearly equal values for these compounds. However, in the previous PAC studies by Rivas et al. [7], the dehydrated product of ZrF4 ·3H2 O at 325 K was found to be ZrF4 , but no intermediate ZrF4 ·H2 O was observed. On the other hand, Waters [10] and Gaudreau et al. [11] reported ZrF4 ·H2 O as the thermolysis product of ZrF4 ·3H2 O. Present investigations have, therefore, been carried out to find whether the dehydration of ZrF4 ·3H2 O is routed through the intermediate monohydrate ZrF4 ·H2 O. If this is observed, our aim is to find whether these two Zr compounds have dissimilar crystal structures as reported from X-ray diffraction measurements [6]. The values of quadrupole frequency (ωQ ) and asymmetry parameter () can be compared to determine the similarity/dissimilarity of crystal structures in ZrF4 ·3H2 O and ZrF4 ·H2 O. Here, the temperature of the crystallized sample formed initially (ZrF4 HF·2H2 O) by dissolving natural Zr metal in concentrated HF and drying at ∼60 ◦ C under infrared has been varied accurately in small steps of 5 K to observe the crystalline phases produced at different temperatures. Perturbed angular correlation technique is

C.C. Dey / Chemical Physics Letters 612 (2014) 8–13

sensitive enough to find the microstructural changes in the sample with temperature. In the temperature range 298–363 K, different zirconium compounds viz. ZrF4 ·HF·2H2 O, ZrF4 ·3H2 O, ZrF4 ·H2 O, Zr2 OF6 ·H2 O, ZrF4 and ZrO2 have been found to be produced. Through careful analysis of temperature dependent PAC spectra, these compounds have been identified and characterized in the present report. Probably, the compounds ZrF4 ·HF·2H2 O, ZrF4 ·H2 O and Zr2 OF6 ·H2 O have been characterized by PAC for the first time. In the dehydration process from ZrF4 ·3H2 O to ZrF4 , the two monohydrates ZrF4 ·H2 O and Zr2 OF6 ·H2 O have been found to be produced as intermediate phases. Regarding the compound ZrF4 , it is difficult to crystallize at room temperature because of its hygroscopic nature and also the PAC signals of ZrF4 and ZrO2 are very similar. Both these compounds have nearly equal values of quadrupole frequency and asymmetry parameter [3] and it is, therefore, really difficult to discriminate these two compounds by PAC. Through our systematic measurements the signals due to ZrF4 and ZrO2 have been clearly identified and have been characterized by PAC. From the earlier PAC measurement [12] confusing results about ZrF4 were reported. 2. Experimental details A tiny piece of natural Zr metal (∼5% Hf) procured from M/S Alfa Aesar is dissolved in concentrated HF. A natural Hf metal also procured from M/S Alfa Aesar was activated to 181 Hf in the Dhruva reactor at Mumbai (flux ∼1013 /cm2 /s). Approximately 1 mg active Hf metal is then dissolved in concentrated HF. A very small drop of active solution is taken and added to the solution of Zr metal in HF. The resulting solution is dried under an infrared lamp at ∼60 ◦ C and the crystallized sample has been used for perturbed angular correlation measurements. The activity of a sample for PAC measurement is typically 50–100 ␮Ci. The TDPAC technique is based on substituting a small or trace amount of radioactive isotope into a well-defined chemical environment in a crystal [13]. Due to interaction of the surrounding electric field gradient (EFG) generated at the nuclear site with the nuclear quadrupole moment, the ␥–␥ angular correlation is perturbed. The perturbation function Gk (t) for k = 2 can be written as [13],



G2 (t) = S20 ()+

3  i



−(ωi R )2 S2i () cos(ωi t) exp(−ıωi t)×exp 2



(1)

For 133–482 keV ␥–␥ cascade of 181 Ta used for present measurements, a consideration of k = 2 only is quite reasonable because of the much smaller value of A4 compared to A2 (A2 = −0.288, A4 = −0.076 [13]). A value of G2 (t) = 1 corresponds to no perturbation. The above expression for G2 (t) is valid for a polycrystalline sample and for I = 5/2 of the intermediate state. The frequencies ωi correspond to transitions between the sublevels of the intermediate state which arise due to the nuclear quadrupole interaction (NQI). For analysis of experimental data, the source inhomogeneities arising from lattice imperfections or chemical effects have been taken into account through the first exponential (Lorentzian damping). Finite time resolution of the coincidence system has also been considered in the data analysis through the second exponential in Eq. (1). If more than one interaction frequencies are present in the sample due to the existence of either various inequivalent sites within the same compound or due to mixture of different compounds,  i the perturbation function can be written as f G (t), where fi is the fraction of the ith component. G2 (t) = i i 2

9

A fitting to expression (1) determine the maximum component Vzz of the electric field gradient through the relation ωQ = eQVzz /4I(2I − 1), ωQ is the quadrupole frequency and Q is the nuclear quadrupole moment of the intermediate state. For an axially symmetric EFG ( = 0), ωQ is related to ω1 , ω2 and ω3 by ωQ = ω1 /6 = ω2 /12 = ω3 /18. For  = / 0, this simple relation of ω1 :ω2 :ω3 = 1:2:3 does not hold and a more complex relation between ωQ and ω1 arises. The asymmetry parameter is defined as the ratio  = (Vxx − Vyy )/Vzz and its value lies between 0 and 1. The indigenous 181 Hf probe undergoing ␤− decay to 181 Ta (T1/2 = 42.4 d) has been used for present measurements. In the decay, 181 Hf populates (93%) the 615 keV excited level (T1/2 = 18 ␮s) which emits two successive ␥-rays, 133 and 482 keV passing through the 482 keV intermediate level with a half-life 10.8 ns and a spin angular momentum 5/2+ [14]. The angular correlation of this cascade is perturbed due to interaction of the electric quadrupole moment of the 482 keV level (2.35b) and the EFG generated at the nuclear site due to the charge distribution of the surrounding medium. The TDPAC spectrometer used for present measurements consists of four BaF2 detectors with crystal sizes of 50.8 mm × 50.8 mm (cylindrical) to acquire four coincidence spectra at a time (two at 180◦ and two at 90◦ ). Details of the experimental set up and data analysis have been described in our earlier letter [15]. For measurements at different temperatures, a closed cycle liquid circulator unit made of M/S Julabo, Germany has been used. The temperature stability was better than ±1 K. The sample in a plastic vial was placed in close contact with the flowing liquid through a copper tube. For measurements above room temperature, water is used as a circulating liquid.

3. Results and discussion Just after crystallizing the solution of Zr in concentrated HF under IR, the resulting PAC spectrum at room temperature is shown in Figure 1. The spectrum gives a pure single frequency component. Analyzing the spectrum, values of quadrupole frequency and asymmetry parameter have been found to be ωQ = 118.6(6) Mrad/s,  = 0.96(1) with a frequency distribution width ı = 0. The data analysis has been done by considering free Skn coefficients (Eq. (1)) as the microcrystallines formed are found to have preferred orientation (texture) and are not perfectly polycrystalline. Above values of ωQ and  can be compared with the corresponding values found in HfF4 ·HF·2H2 O reported by Thies et al. [16] and Butz et al. [17]. In HfF4 ·HF·2H2 O, values of ωQ = 126.69(4) Mrad/s and  = 0.9241(4) were reported by Butz et al. [17] which are in good agreement with the results reported by Thies et al. [16]. The present crystallized sample gives values of ωQ and  closer to these and suggests that it has been crystallized in the form ZrF4 ·HF·2H2 O. This also indicates that the compounds HfF4 ·HF·2H2 O and ZrF4 ·HF·2H2 O are isostructural. To the best of our knowledge, no results of PAC measurements in ZrF4 ·HF·2H2 O exist in the literature. However, ZrF4 ·HF·2H2 O has been found to be unstable and at room temperature it gives a new PAC signal corresponding to a different component after one to two days. This new signal has been characterized by ωQ = 184.5(5) Mrad/s,  = 0.843(5) with a value of ı = 1.1(3)%. The new frequency component found at room temperature can be attributed to ZrF4 ·3H2 O by comparing with previous reported results [7] and it grows with time at the expense of the other. It is found that within a few days a component fraction ∼78% due to ZrF4 ·3H2 O is obtained while the remaining fraction (22%) is due to ZrF4 ·HF·2H2 O. Evolution from ZrF4 ·HF·2H2 O to ZrF4 ·3H2 O with time is shown in Figure 1.

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C.C. Dey / Chemical Physics Letters 612 (2014) 8–13 6

0 .1 0

Just after crystallization

0 .0 5 4

0 .0 0

(ZrF4.HF.2H2O)

- 0 .0 5 2

- 0 .1 0

I(ω) (arb. unit)

- 0 .1 5

A2G2 (t)

.1 0 - 0 .2 0 .0 5 0 .0 0 - 0 .0 5 - 0 .1 0 - 0 .1 5

0 6

Next day

4

2

0 4

- 0 .1 .2 0 0 .0 5

After 3 days of preparation

3

0 .0 0 2

- 0 .0 5

1

- 0 .1 0 - 0 .1 5 - 0 .2 0

0 0

10

20

30

40

0

50

1

2

3

4

5

6

ω (Grad/s)

t (ns)

Figure 1. PAC spectra at room temperature showing gradual evolution from ZrF4 ·HF·2H2 O to ZrF4 ·3H2 O. Left panel shows time spectra and the right panel shows the corresponding Fourier cosine transforms.

0 .1 0

3

0 .0 5

313K

2

0 .0 0 -0 .0 5

1

-0 .1 0 -0 .1 5

0

10 -0 .2

3

0 .0 5

318K

2

0 .0 0 -0 .0 5

1

-0 .1 0 -0 .1 5

0

-0 .2 10

3

I(ω) (arb. unit)

A2G2(t)

0 .0 5 0 .0 0 -0 .0 5 -0 .1 0 -0 .1 5 - 0 .. 2 10

323K

2

1 0 3

0 .0 5

333K

2

0 .0 0 -0 .0 5

1

-0 .1 0 -0 .1 5

0

10 -0 .2

3

0 .0 5

-0 .0 5

1

-0 .1 0 -0 .1 5 -0 .2 0

343K

2

0 .0 0

0 0

10

20

30

t (ns)

40

50

0

1

2

3

4

5

6

ω (Grad/s)

Figure 2. Temperature dependent PAC spectra showing change in chemical components with increase in temperature. Left panel shows time spectra and the right panel shows the corresponding Fourier cosine transforms.

C.C. Dey / Chemical Physics Letters 612 (2014) 8–13

11

Table 1 Results of PAC measurements at different temperatures in the crystallized sample ZrF4 ·HF·2H2 O. Temp. (K)

Comp.

ωQ (Mrad/s)



ı (%)

f (%)

Assignment

100

ZrF4 ·HF·2H2 O

298

1

118.6 (6)

0.96 (1)

0

298a

1 2

183.7 (1) 118.7 (2)

0.849 (1) 1 (fixed)

0.77 (7) 1.3 (3)

78 (1) 22 (1)

313

1 2 3 4

184.7 (5) 123.3 (9) 135 (2) 155 (4)

0.847 (8) 0.92 (2) 0.40 (3) 0.62 (5)

0.8 (3) 1.3 (7) 0 0

57 (1) 26 (1) 7 (1) 10 (1)

318

1 2 4

109.6 (3) 136 (2) 163 (1)

0.49 (1) 0.44 (3) 0.60 (3)

1.9 (5) 0 0

77 (2) 9 (1) 14 (1)

323

1 2 4

112.7 (4) 133 (1) 153 (2)

0.47 (2) 0.29 (4) 0.61 (3)

2.3 (4) 0 0

80 (3) 11 (1) 9 (1)

333

1 2

110.2 (4) 134 (1)

0.43 (2) 0.33 (2)

2.6 (5) 0

79 (3) 21 (3)

343

1 2 3

121 (1) 109 (1) 6.4 (5)

0.39 (1) 0.32 (3) 0

12 (1) 0 0

84 (1) 5 (1) 11 (1)

353

1 2 3

125 (2) 111 (1) 8.3 (8)

0.36 (2) 0.38 (3) 0

11 (1) 0 0

80 (2) 8 (1) 12 (1)

363

1 2 3

127 (2) 111 (1) 6.8 (6)

0.37 (2) 0.44 (3) 0

12 (1) 0 0

81 (2) 8 (1) 11 (1)

a

ZrF4 ·3H2 O

ZrF4 ·H2 O Zr2 OF6 ·H2 O ZrF4

ZrO2

After 3 days of preparation.

The sample is now heated at 313 K. The resulting spectrum is shown in Figure 2. At 313 K, the spectrum produces four frequency components. The results obtained for different components along with their relative fractions are shown in Table 1. At this elevated temperature, the component due to ZrF4 ·3H2 O is slightly reduced and along with ZrF4 ·HF·2H2 O two other new frequency components are found to be produced. The component fraction for ZrF4 ·HF·2H2 O is not changed appreciably. One new frequency component gives values of ωQ = 155(4) Mrad/s,  = 0.62(5) and this can be attributed to Zr2 OF6 ·H2 O. This assignment can be justified from the consideration that similar values of ωQ and  were reported in the analogous compound Hf2 OF6 ·H2 O where values of ωQ = 161.7(3) Mrad/s,  = 0.761(4) [17] were reported. The results in Zr2 OF6 ·H2 O and Hf2 OF6 ·H2 O indicate that these have same crystal structures. The second new component (7%) can possibly be assigned to ZrF4 ·H2 O and this is produced by dehydrating two water molecules of ZrF4 ·3H2 O. The monohydrate ZrF4 ·H2 O component was found earlier [10,11] as the thermolysis product of ZrF4 ·3H2 O above 350 K but Rivas et al. [7] somehow missed to find this monohydrate component from their PAC measurements. Here, the dehydrated product ZrF4 ·H2 O appears at a slightly lower temperature and it shows as a minor component. However, comparing the results in ZrF4 ·3H2 O and ZrF4 ·H2 O, it is found that values of quadrupole frequency and asymmetry parameters for these two components are completely different and indicates that crystal structures for ZrF4 ·3H2 O and ZrF4 ·H2 O are not similar unlike the two hafnium analogous compounds. From X-ray diffraction studies [6] also, different crystal structures for ZrF4 ·3H2 O and ZrF4 ·H2 O were observed. Now, the PAC measurement is performed at a slightly higher temperature of 318 K. At this temperature, the component due to ZrF4 ·3H2 O completely disappears and instead of a new frequency component is observed. Values of ωQ and  for the new component are found to be ωQ = 109.6(3) Mrad/s,  = 0.49(1) with a value of ı = 1.9(5)%. The new component can be considered as the

dehydrated product ZrF4 and it appears as a major fraction (77%) at this temperature. Present values of ωQ and  found for this new component can be compared with the previously reported values in ZrF4 [12]. In fact, Rivas et al. [12] reported values of ωQ = 123(2) Mrad/s,  = 0.32(2) in ZrF4 at room temperature and these are not in good agreement with the present values. In the earlier report [12], the sample was prepared by heating ZrF4 ·3H2 O to moderate temperatures and most like they produced ZrO2 by this heating. This can be argued from the consideration that the spin rotation curves in their measurements were unchanged up to 530 K which is quite unlikely unless it was already oxidized in the original sample. On the other hand, present results found for the new component are quite closer to the values found for the analogous HfF4 where values of ωQ = 116(2) Mrad/s,  = 0.37(2) at room temperature were reported [2] and presents evidence that both HfF4 and ZrF4 have the similar crystal structure as expected. It can be mentioned here is that Rivas et al. [7] reported a complete dehydration producing ZrF4 directly from ZrF4 ·3H2 O at a temperature 325 K without forming any intermediate monohydrate. However, no values of ωQ and  for ZrF4 were reported there in. Our measurement at 318 K also produces two other components due to ZrF4 ·H2 O and Zr2 OF6 ·H2 O (Table 1). At a temperature of 323 K, the component fractions do not change appreciably compared to that observed at 318 K (Table 1). But, at 333 K, one minor component due to Zr2 OF6 ·H2 O vanishes and we obtain the anhydrous ZrF4 and ZrF4 ·H2 O only at this temperature. Both the anhydrous ZrF4 and the monohydrate ZrF4 ·H2 O are found to be enhanced at 333 K. The monohydrate fraction is found to be ∼21% and the anhydrous component gives ∼79%, both are maximum in the whole temperature region. The coexistence of ZrF4 along with ZrF4 ·H2 O is quite likely since the anhydrous ZrF4 is known to be hygroscopic. This gives an additional support about identification of the two fractions and the results are consistent with those at lower temperatures.

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C.C. Dey / Chemical Physics Letters 612 (2014) 8–13 3

0 .1 0 0 .0 5

2

0 .0 0 -0 .0 5

1

-0 .1 0 0

10 -0 .2

3

I(ω) (arb. unit)

-0 .1 5

A2G2 (t)

0 .0 5 0 .0 0 -0 .0 5 -0 .1 0 -0 .1 5

2

1 0 3

10 -0 .2 0 .0 5

2

0 .0 0 -0 .0 5

1

-0 .1 0 -0 .1 5 -0 .2 0

0 0

10

20

30

40

50

0

1

t (ns)

2

3

4

5

6

ω (Grad/s)

Figure 3. PAC spectra at room temperature after heating the sample at temperatures 318 K (top), 323 K (middle) and 363 K (bottom). Left panel shows time spectra and the right panel shows the corresponding Fourier cosine transforms.

Now, PAC measurement has been performed at a more elevated temperature of 343 K where the PAC spectrum is found to be changed (Figure 2). At this temperature, a new frequency component (∼84%) arises along with the very small component due to ZrF4 (∼5%). The values of ωQ and  for the new component have been found to be ωQ = 121(1) Mrad/s,  = 0.39(1) with a value of ı ∼ 12%. This new frequency component can be attributed to ZrO2 by comparing with the previous reported results in ZrO2 [1,2]. At room temperature, results of ωQ and  in ZrO2 were reported to be ωQ = 123(1) Mrad/s,  = 0.337(7), ı = 4% [1] and similar values were obtained in HfO2 . In the present sample, it produces a relatively higher value of ı. This is probably due to the fact that here ZrO2 is produced thermally from ZrF4 and a chemical in-homogeneity in the sample is expected. This indicates that the sample gets oxidized almost completely at 343 K. A third weak component is also observed at this temperature which is probably due to a crystalline defect produced at this temperature. The PAC spectra and the component fractions do not change much at still higher temperatures up to 363 K (Table 1). The measurements have been repeated at room temperature after the sample is heated to 318, 323 and 363 K. The PAC spectra found at room temperature after heating at different higher temperatures are shown in Figure 3. The results obtained are tabulated in Table 2. It is found that after heating at 318 K, the PAC

spectrum gives mainly two components. The major component is found to be due to ZrF4 ·3H2 O (∼60%) while the second component (∼40%) is due to Zr2 OF6 ·H2 O. Here, a much stronger signal for zirconium oxi-fluoride is obtained at room temperature. At 318 K, however, the sample produced the anhydrous ZrF4 (∼77%), ZrF4 ·H2 O (∼9%) and Zr2 OF6 ·H2 O (∼14%). The results at room temperature after heating at 318 K indicate that ZrF4 is very hygroscopic and it becomes trihydrate by attracting three water molecules. The ZrF4 ·H2 O is also fully hydrated when cooled at room temperature. The results obtained at room temperature after heating the sample at 323 K (Table 2) gives a little fraction for ZrF4 (∼13%) where the major fraction is due to ZrF4 ·3H2 O (∼78%) as expected. This small fraction for ZrF4 , however, is important and gives the values of ωQ and  at room temperature through this measurement only. The values are found to be ωQ = 106(2) Mrad/s,  = 0.55(3). Contrary to this, previous results in ZrF4 were reported to be [12] ωQ = 123(2) Mrad/s,  = 0.32(2). These values, therefore, really do not correspond to ZrF4 but to ZrO2 as discussed above. This can be confirmed again from our room temperature measurement after heating the sample at 363 K where it produces ZrF4 ·3H2 O (∼39%) and ZrO2 (∼48%). The room temperature values for ZrO2 closely agree with the values reported in reference [1]. There is a third weak component which is probably due to crystalline defect.

Table 2 Results of PAC measurements at room temperature after heating the sample at different temperature. Heated temp. (K)

Comp.

ωQ (Mrad/s)



ı (%)

318

1 2

183.8 (1) 155 (1)

0.847 (3) 0.62 (1)

0.6 (1) 3.5 (4)

61 (1) 39 (1)

ZrF4 ·3H2 O Zr2 OF6 ·H2 O

323

1 2 3

184.4 (2) 106 (2) 8.2 (7)

0.842 (2) 0.55 (3) 0

1.0 (1) 5 (1) 0

78 (1) 13 (1) 8 (1)

ZrF4 ·3H2 O ZrF4

363

1 2 3

184.2 (3) 119 (1) 6.9 (3)

0.850 (3) 0.37 (2) 0

0.4 (2) 13.0 (7) 0

39 (1) 48 (1) 13 (1)

ZrF4 ·3H2 O ZrO2

f (%)

Assignment

C.C. Dey / Chemical Physics Letters 612 (2014) 8–13

13

4. Summary and conclusion Different Zr compounds that are formed by heating at different temperatures can be summarized as following.

ZrF4.HF.2H2O (100%)

RT

ZrF4.3H2O (78%) ZrF4.HF.2H2O(22%)

ZrF4(77%)

ZrF4.3H2O (57%)

313 K

ZrF4.HF.2H2O (26%)

318 K

ZrF4.H2O (7%)

ZrF4.H2O(9%) Zr2OF6.H2O(14%)

Zr2OF6.H2O (10%)

323K

ZrO2(84%) ZrF4(5%)

343 K

ZrF4(79%) ZrF4.H2O(21%)

333 K

ZrF4(80%) ZrF4.H2O(11%) Zr2OF6.H2O(9%)

The crystallized compound ZrF4 ·HF·2H2 O synthesized for the first time shows that it has similar crystal structure with its hafnium analog HfF4 ·HF·2H2 O. The trihydrate ZrF4 ·3H2 O and the monohydrate ZrF4 ·H2 O are not isostructural unlike the structural similarity that are found in HfF4 ·3H2 O and HfF4 ·H2 O. The anhydrous ZrF4 has been found to be very hygroscopic unlike HfF4 and is difficult to get at room temperature. However, both ZrF4 and HfF4 are found to be isostructural. The most stable configuration of the zirconium fluoride system is the trihydrate ZrF4 ·3H2 O. The component due to Zr2 OF6 ·H2 O has been identified for the first time. The results in Zr2 OF6 ·H2 O and Hf2 OF6 ·H2 O show that these also have similar structures. However, no anhydrous zirconium analog of Hf2 OF6 was found from previous XRD measurements [6]. It is found that ZrF4 gets oxidized almost completely at a temperature 343 K when heated in air producing ZrO2 . From present measurements it has been found that final thermolysis product of ZrF4 ·3H2 O is ZrO2 and the intermediate phases are ZrF4 ·H2 O, Zr2 OF6 ·H2 O and ZrF4 . Our final conclusion is that PAC is a very useful technique for microstructural analysis of a crystallized sample. Acknowledgement The research work is supported by the Department of Atomic Energy, Government of India.

References [1] A. Ayala, R. Alonso, A. López-García, Phys. Rev. B 50 (1994) 3547. [2] J.A. Martínez, M.C. Caracoche, A.M. Rodríguez, P.C. Rivas, A.R. López García, Chem. Phys. Lett. 102 (1983) 277. [3] A.M. Rodríguez, J.A. Martínez, M.C. Caracoche, P.C. Rivas, A.R. López García, S. Spinelli, J. Chem. Phys. 82 (1985) 1271. [4] J.A. Martínez, M.A. Caracoche, P.C. Rivas, M.T. Dova, A.M. Rodríguez, A.R. López García, Phys. Rev. B 35 (1987) 5244. [5] A. Lerf, T. Butz, Hyperfine Interact. 36 (1987) 275. [6] C.E.F. Rickard, T.N. Waters, J. Inorg. Nucl. Chem. 26 (1964) 925. [7] P.C. Rivas, A.M. Rodríguez, M.T. Dova, M.C. Caracoche, J.A. Martínez, A.R. López García, Hyperfine Interact. 39 (1988) 181. [8] F. Gabela, B. Kojíc-Prodíc, M. Sljukíc, Z. Ruzíc-Toros, Acta Crystallogr. B 33 (1977) 3733. [9] D. Hall, C.E.F. Rickard, T.N. Waters, J. Inorg. Nucl. Chem. 33 (1971) 2395. [10] T.N. Waters, J. Inorg. Nucl. Chem. 15 (1960) 320. [11] B. Gaudreau, Rev. Chim. Miner. 2 (1965) 1. [12] P.C. Rivas, M.C. Caracoche, J.A. Martínez, M.T. Dova, A.R. López García, Hyperfine Interact. 30 (1986) 49. [13] G. Schatz, A. Weidinger, Nuclear Condensed Matter Physics: Nuclear Methods and Application (J.A. Gardner, Trans.), John Wiley and Sons, Chichester/New York/Brisbane/Toronto/Singapore, 1996, pp. 63 (Chapter 5). [14] R.B. Firestone, V.S. Shirley, Table of Isotopes, 8th edn., John Wiley and Sons, New York, 1996. [15] C.C. Dey, Pramana 70 (2008) 835. [16] W.G. Thies, H. Appel, R. Heidinger, G.M. Then, Hyperfine Interact. 30 (1986) 153. [17] T. Butz, S.K. Das, Y. Manzhur, Z. Naturforsch. 64A (2009) 103.