- Email: [email protected]
Structural phase transition and ferroelasticity in (H2NNH3)3CdBr5 crystal
Accepted Manuscript Structural phase transition and ferroelasticity in (H2NNH3)3CdBr5 crystal Z. Czapla, J. Janczak, O. Czupiński, J. Przesławski, M. Crofton PII:
S0022-3697(18)31632-9
DOI:
10.1016/j.jpcs.2018.09.005
Reference:
PCS 8718
To appear in:
Journal of Physics and Chemistry of Solids
Received Date: 16 June 2018 Revised Date:
22 August 2018
Accepted Date: 6 September 2018
Please cite this article as: Z. Czapla, J. Janczak, O. Czupiński, J. Przesławski, M. Crofton, Structural phase transition and ferroelasticity in (H2NNH3)3CdBr5 crystal, Journal of Physics and Chemistry of Solids (2018), doi: 10.1016/j.jpcs.2018.09.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Structural phase transition and ferroelasticity in (H2NNH3)3CdBr5 crystal Z. Czapla1, J. Janczak2, O. Czupiński3, J. Przesławski4∗, M. Crofton4 1
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Department of Physics, Opole University of Technology, Ozimska 75, 45-370 Opole, Poland 2 Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2, 50-422 Wrocław, Poland 3 Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland 4 Institute of Experimental Physics, University of Wrocław, Max Born Sq. 9, 50-204 Wrocław, Poland
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Abstract
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Single crystals of (H2NNH3)3CdBr5 were grown and their properties were investigated. DSC, DTG, structural studies, optical polarized microscopy observations and dielectric studies are presented. TGA showed the stability of the substance up to about 455 K and decomposition above this temperature. DSC studies revealed the first order structural phase transitions at 294/292 on heating/cooling runs. X-ray structural studies showed a change of symmetry from orthorhombic to monoclinic and the transition seems to belong to the mmmF2/m Aizu’s species. In optical studies performed with a polarizing microscope, the ferroelastic type of domain structure and the phase front appearance were observed. Dielectric measurements clearly evidenced the first-order phase transition as a jump-like decrease of permittivity on cooling and increase on heating. Structural and dielectric studies indicate the order-disorder character of the phase transition.
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Highlights:
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Keywords: organic – inorganic compounds; structural studies, phase transitions; DSC, DTA, DTG measurements; dielectric properties, optical observations;
Examination of the structural phase transition in the (H2NNH3)3CdBr5 was performed The transition proceeds between two centrosymmetric groups Cmcm ↔ P21/m The transition is of the first order and has the order – disorder character
Ferroelastic domain structure is typical for the mmmF2/m of the Aizu`s species
Corresponding author: [email protected]
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ACCEPTED MANUSCRIPT 1. Introduction Cadmium chloride and bromide form a large family of hybrid organic-inorganic compounds containing various anionic sublattices. Interesting structures and phase transitions were found
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in perovskite type compounds containing different amine cations. Halogenocadmate compounds form various structural architectures from which crystals with desired physical properties can be obtained [1,2]. Taking into account the role of cadmium in biological processes [3], compounds of this metal are an interesting subject of study. Among them one mention
[(CH2)3(NH3)2]CdCl4
[4,5],
[(CH2)3(NH3)2]CdBr4
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can
[6,7]
and
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[(CH3)2CHNH3)]4Cd3Cl10 [8,9] with a polymer anionic structure that exhibits structural phase transitions. Interesting structures of cadmium compounds were determined in the case of salts with hydrazinium and guanidinium cations [10]. The (H2NNH3)3CdBr5 (tris-hydrazinium pentabromocadmate (II)) and the [C(NH2)3]Cd2Br5 (guanidinium pentabromodicadmate (II) show anionic sublattices of perovskite type and on the basis of NQR [10] and DSC studies
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exhibit structural phase transitions. In the case of the inorganic (H2NNH3)3CdBr5 compound two structural first-order phase transitions were noticed in DSC, namely: at about 445 K and
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294 K. At about 450 K, melting of the substance was observed with consequent decomposition. In NQR studies the transition was reported at 304 K, corresponding to that
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seen at 294 K in DSC. On the ground of X-ray studies the crystal was proposed to crystallize in the polar space group P21 [10] at 300 K and this symmetry was elucidated for the low temperature phase. Above the phase transition the symmetry was assumed to be P21/m [10]. The proposed change of symmetry is typical for ferroelectric phase transitions. Thus, it is suggested that the transition observed in (H2NNH3)3CdBr5 should be that of a paraelectricferroelectric one. However, it is doubtful that the symmetry found at 300 K is the symmetry of the low temperature phase. The structure studied at 300 K can be related to the phase existing above
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ACCEPTED MANUSCRIPT 294 K. To describe the phase transition and properties of the crystal we decided to grow single crystals of this substance, and aimed to study the character of the phase transition and its properties in some temperature range around the phase transition at about 294 K, where
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ferroelectricity is expected.
2. Experimental 2.1. Preparation.
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Polycrystals were obtained from a water solution of stoichiometric quantities of hydrazinium bromide, cadmium bromide CdBr2·2H2O and a small excess of hydrobromic acid. Thin
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needle-like crystals were obtained after slow evaporation at room temperature. These crystals were dissolved in water with a small excess of hydrobromic acid and then the solution was evaporated at a constant temperature of 305 K. After evaporation thicker needles were chosen as germs for the growth of single crystals. Using the selected germs the single crystals were
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grown from the saturated solution at a constant temperature of 305 K. The crystals elongated along the a-axis (2-3 cm) with an area perpendicular to the a-axis of 4 x 6 mm2 and were obtained during 4-5 weeks. This allowed us to prepare plates of area 10-15 mm2 and thickness
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of about 0.5-0.7 mm for dielectric and optical studies. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were carried out
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by means of a Seteram SETSYS 16/18 instrument in the temperature range 295 – 780 K on a heating run at a rate of 2 K/min. The heat flow studies were performed using a Perkin-Elmer 8500 differential scanning calorimetry (DSC) at heating-cooling rates of 20 and 10 K/min in the temperature range 120 – 350 K, respectively.
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ACCEPTED MANUSCRIPT 2.2. Single crystal X-ray data collection. X-ray diffraction (intensity) data for the crystal were collected using graphite monochromatic MoKα radiation on a four-circle κ geometry KUMA KM-4 diffractometer with a twodimensional area CCD detector at 310(1), 296(1) and 278(1) K. The ω-scan technique with
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∆ω = 1.0º for each image was used for data collection. The unit cell parameters were refined by the least-squares method on the basis of all measured reflections. One image was used as a standard after every 40 images for monitoring of the crystal stability and data collection, and
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no correction on the relative intensity variations was necessary. Data collection was made using the CrysAlis CCD program [11]. Integration, scaling of the reflections, correction for
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Lorenz and polarisation effects and absorption corrections were performed using the CrysAlis Red program [11]. The structure at 310(1) and 296(1) K was solved by direct methods using SHELXS [12] and refined using SHELXL-2014 programs [13]. The hydrogen atoms were not localised. The final difference Fourier maps showed no peaks of chemical significance.
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Obtaining the structure solution at 278(1) was unsuccessful due to the crystal twinning. Details of the data collection parameters, crystallographic data and final agreement parameters are collected in Table 1. Selected geometrical parameters are listed in Table 2.
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Visualisation of the structure was made with the Diamond 3.0 program [14].
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2.3. Physical studies.
Optical observations were done by means of a polarizing microscope in the temperature range 280 – 320 K on cooling and heating runs. The samples were placed in an LINKAM THM-600 heating/cooling stage. For microscopic observations thin crystalline plates were used. The rate of cooling/heating close to the phase transition temperature was 0.2 K / min. Dielectric measurements were performed with a HP computer controlled system at a frequency of 1 kHz and a temperature range of 250 - 320 K on a cooling/heating run along three crystallographic axes. Silver paste was used as electrodes.
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ACCEPTED MANUSCRIPT 3. Results of experimental measurements and discussion 3.1. Crystals Transparent single crystals in the shape of long rods were of good quality for dielectric studies and optical observations. A habit of the crystal resembles clearly orthorhombic symmetry.
experimental studies. 3.2. DTA and TGA studies
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Results of DTA and TGA studies are presented in Fig. 1.
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However, the crystals are very fragile, break easily and it was difficult to prepare samples for
Fig. 1. Temperature dependence of the DTA and TGA signals for the (H2NNH3)3CdBr5 crystal.
The TGA studies showed thermal stability up to 454 K, however in the vicinity of this temperature a double anomaly on the DTA curve is observed. It is most likely the structural 5
ACCEPTED MANUSCRIPT phase transition followed by melting and decomposition of the substance. This situation was pointed out in [10].
3.2. DSC studies
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Looking at the DTA and TGA studies we decided to study the transition at 294 K where ferroelectricity is expected. The heat flow observed in the DSC studies is presented in Fig. 2.
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The studies were done around the phase transition predetermined at 294 K [10].
Fig. 2. Heat flow as a function of temperature for (H2NNH3)3CdBr5
As can be clearly seen, the anomaly observed indicates a first order phase transition. The transition is fully reversible and temperature hysteresis is about 2 K, as deduced from the 6
ACCEPTED MANUSCRIPT onset anomalies presented above. The transition enthalpy and entropy are equal to 1.7 kJ/mol and 5.8 J/molK, respectively. Both temperature and thermal quantities are in agreement with those presented in [10]. The entropy change is approximately equal to Rln2 and indicates the
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order-disorder character of the phase transition.
3.3. Description of structure
To describe the phase transition the structure of the crystal was studied. Taking into account
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basic crystallographic data are presented in Table 1.
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the appearance of a structural phase transition we checked the symmetry of both phases. The
Table 1. Crystal data for two phases for (H2NNH3)3CdBr5 Temperature (K)
310
Empirical formula
CdBr5H15N6 orthorhombic
278
CdBr5H15N6
CdBr5H15N6
orthorhombic
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Crystal system
296
monoclinic
Cmcm
Cmcm
P21/m
a (Å)
11.8642(6)
11.8618(4)
11.7423(8)
b (Å)
14.6580(8)
14.6859(5)
14.7430(16)
7.7933(5)
7.8062(3)
15.5944(30)
90.0
90.0
89.821(14)
90.0
90.0
90.00
90.0
90.0
90.00
V (Å3)
1355.30(13)
1359.85(8)
2699.65(14)
Z
4
4
8
µ (mm–1)
16.323
16.323
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Space group
α (0) β(0) γ(0)
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c (Å)
Crystal size (mm)
0.28 × 0.26 × 0.22
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ACCEPTED MANUSCRIPT Radiation type, λ (Å) θ range(o)
Mo Kα, 0.71073 3.418-27.864
3.423-29.482
Structural analysis showed orthorhombic symmetry of the (H2NNH3)3CdBr5 crystal at 310 K
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and 296 K and the space group Cmcm (point group mmm). The molecular structure at 310 K and 296 K is almost the same and is illustrated in Figs. 3 and 4. An asymmetric unit of (H2NNH3)3CdBr5 consists of half of a distorted CdBr6 octahedron (Table 2) and one and a
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half NH2NH3+ cations. Both hydrazinium cations are disordered, however in one, the nitrogen atom (N1) is shared between both orientations, whereas in the second hydrazinium cation
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both nitrogen atoms (N3 and N4) statistically occupy two positions (see Fig. 4). Each distorted CdBr6 octahedron has two shared Br atoms with its neighbours forming a onedimensional zig-zag coordination polymer {CdBr5}n along the c-axis. Although the hydrogen atoms of the disordered hydrazinium cations were not localized, the hydrazinium cations
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interact with each other via NH…N hydrogen bonds forming chains along the c-axis, since the N…N distances within the chain are 2.945(7) Å {N2…N3}, 2.924(12) Å {N3…N3#, (#) x, -
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y, -z) and 3.004(13) Å {N4…N4#; symmetry code (#) x, -y, -z}.
Fig. 3. View of molecular structure of (H2NNH3)3CdBr5 (symmetry code: (i) 1-x, 1-y, 0.5+z; (ii) x, y, 0.5-z; (iii) 1-x, y, 0.5-z).
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Fig. 4. Molecular packing of (H2NNH3)3CdBr5 showing the zig-zag coordination polymer of
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{CdBr5}n and disordered NH2NH3+ cations viewed along a-axis.
Table 2. Selected geometrical parameters for (H2NNH3)3CdBr5.
CdBr1 x2
310(1)K
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Temperature
296(1)K
2.8358(4)
2.8420 (3)
2.6793(7)
2.6828 (6)
CdBr3 x2
2.7491(6)
2.7498 (5)
N1—N2
1.213(4)
1.227 (4)
N3—N4
1.212(5)
1.209 (5)
Br1—Cd1—Br3
86.070(15)
86.011 (12)
Br2—Cd1—Br3
93.669(13)
93.711 (10)
Br2i—Cd1—Br3
93.669 (13)
93.711 (10)
Br2—Cd1—Br2i
94.59(3)
94.86 (3)
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CdBr2 x2
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86.795(15)
86.736 (12)
Br2—Cd1—Br1iii
176.10(2)
175.938 (18)
Symmetry code: : (i) 1-x, 1-y, 0.5+z; (ii) x, y, 0.5-z; (iii) 1-x, y, 0.5-z.
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Structural studies at 278 K (below the phase transition temperature) showed a monoclinic structure. However, strong twinning (below the phase transition temperature) prevented the determination of a detailed crystallographic structure at the low temperature phase. Taking
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into account the change of symmetry from orthorhombic to monoclinic phase it is expected that the observed twinning is connected with a phase transition of the ferroelastic type. The
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presence of a symmetry center in both phases excludes the ferroelectricity. Considering the entropy change at the phase transition, and in spite of lack of the detailed structure of the low temperature phase, the molecular mechanism of the transition is expected to be connected
3.4. Optical studies
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with the ordering of hydrazinium cations.
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Looking at the symmetry of the (H2NNH3)3CdBr5 crystal found at 296 K and below the phase transition temperature at 278 K, one can notice that the transition at TC occurs between the
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orthorhombic and monoclinic phases and one deals with the symmetry change Cmcm ↔ P21/m. Thus, the transition is expected to be of ferroelastic type. According to Aizu’s notation [15] the transition can be classified as the mmmF2/m species with two orientation states below the phase transition temperature. Polarizing microscopy observations of the crystal along the a-axis revealed the appearance of a domain structure of ferroelastic type with domain walls in the (010) and (001) planes below 294 K [16]. The notation of the planes is indexed with respect to the orthorhombic axes. The observed domain structure presented in Fig. 5 confirms the transition mmmF2/m. 1
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Fig. 5. The ferroelastic domain structure observed for the a-cut of the (H2NNH3)3CdBr5 crystal (T = 285 K).
3.5. Dielectric studies
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Results of dielectric measurements performed at a frequency of 1 kHz along three
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crystallographic directions are presented in Fig. 6.
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Fig. 6. a) Temperature dependence of the dielectric permittivity measured along the a-axis.
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Fig. 6. b) Temperature dependence of the dielectric permittivity measured along the b-axis.
Fig. 6. c) Temperature dependence of the dielectric permittivity measured along the c-axis.
Heating and cooling around the phase transition temperature showed an anomalous jump-like decrease of permittivity on cooling and an increase on heating, in addition to temperature
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ACCEPTED MANUSCRIPT hysteresis. This is characteristic for a first-order transition. The increase of the dielectric permittivity on heating is connected with the order-disorder mechanism of the transition.
4. Summary
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From the studies presented one can summarize as follows: 1. DSC data revealed the reversible first-order phase transition at 294/292 K on heating and cooling, respectively;
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2. structural X-ray investigations showed the change of symmetry from orthorhombic above the phase transition to monoclinic below the phase transition temperature,
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Cmcm ↔ P21/m;
3. structural studies and optical observations indicate that the phase transition is of ferroelastic type and can be classified as mmmF2/m Aizu’s species; 4. the molecular mechanism of the transition is expected to be connected with the ordering of hydrazinium cations;
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5. dielectric permittivity exhibits jump-like and hysteretic behavior characteristic for the
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first order transition.
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. Supplementary material
Additional material comprising full details of the X-ray data collection and final refinement parameters including anisotropic thermal parameters and a full list of the bond lengths and angles have been deposited with the Cambridge Crystallographic Data Center in the CIF format as supplementary publications no. CCDC 1845071 and 1845072 for 296 and 310 K. Copies of the data can be obtained free of charge on the application to CCDC, 12 Union Road, Cambridge, CB21EZ, UK, (fax: (+44)1223-336-033; email: [email protected] ).
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ACCEPTED MANUSCRIPT References: [1] Ch.E. Costin-Hogan, E. Chen, Ch.-L. Hughes, A. Pickett, R. Valencia, N.P. Rath, A. Beaty, “Reverse engineering: Toward 0-D cadmium halide clusters, CrystEngComm 10 (2008) 1910-1915. http://dx.doi.org/10.1039/B812504J
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[2] A. Thorn, R. Willet, B. Twamley, Retro-Crystal Engineering Analysis of Two NMethylethylenediammonium Cadmium Halide Salts Obtained by Dimensional Reduction and Recombination of the Hexagonal CdX2 Lattice, Cryst. Growth Des. 5 (2005) 673-679. doi:10.1021/cg030059s
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[3] L.G. Marzili, T.J. Kistenmacher, G.I. Eichhorn, Metal ions, in Biology, T.G. Spiro (Ed.) vol.1, Wiley, New York, 1980, p. 179. (104. Marzilli LG, Kistenmacher TJ, Eichhorn GL. Structural principles of metal ion-nucleotide and metal ion-nucleic acid interactions. In: TG Spiro, ed. Nucleic acid-metal ion interactions. New York, NY: John Wiley & Sons, Inc.; 1980.)
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[4] R. Kind, S. Plesko, P. Gauter, J. Ross and J. Fousek, Structural phase transitions in the perovskite-type layer compounds NH3(CH2)3NH3CdCl4, NH3(CH2)4NH3MnCl4, and NH3(CH2)5NH3CdCl4,Phys.Rev. B 23 (1981) 5301-5315. doi.org/10.1103/PhysRevB.23.5301 [5] B. Staśkiewicz, I. Turowska-Tyrk, J. Baran, Cz. Górecki and Z. Czapla, Structural characterization, thermal, vibrational properties and molecular motions in perovskite-type diaminopropanetetrachlorocadmate NH3(CH2)3NH3CdCl4 crystal, J. Phys. Chem. Sol., 75, 12 (2014)1305-1317. doi.org/10.1016/j.jpcs.2014.07.004
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[6] H. Ishihara, S. Dou, K. Horiuchi, V.G. Krishnan, H. Paulus, H. Fuess, A. Weiss, Isolated versus Condensed Anion Structure II; the Influence of the Cations (1,3-propanediammonium, 1,4-phenylendiammonium, and n-propylammonium) on Structures and Phase Transitions of CdBr2-4Salts A 79,81Br NQR and X-ray Structure Analysis, Z. Naturforschung 51a, (1996) 1216-1228. https://doi.org/10.1515/zna-1996-1212
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[7] B. Staśkiewicz, O. Czupiński and Z. Czapla, On some spectroscopic properties of a layered 1,3-diammoniumpropylene tetrabromocadmate hybrid crystal, J. Mol. Struct., 1074, (2014) 723-731. doi.org/10.1016/j.molstruc.2014.05.036 [8] A. Gągor, A. Waśkowska, Z. Czapla and S. Dacko, Structural phase transitions in tetra(isopropylammonium) decachlorotricadmate(II), [(CH3)2CHNH3]4Cd3Cl10, crystal with a two-dimensional cadmium(II) halide network. Acta Cryst. B 67, (2011). 122-129. doi:10.1107/S0108768110054583 [9] B. Staśkiewicz, S. Dacko and Z. Czapla, Successive phase transitions in tetra(isopropylamine)decachlorotricadmate (II) [(CH3)2CHNH3]4Cd3Cl10 crystal - Dielectric and dilatometric studies., Curr. Appl. Phys., 12 (2) (2012) 413-417. doi:10.1016/j.cap.2011.07.039 [10] H. Ishihara, K. Horiuchi, V.G. Krishnan, I. Svoboda, H.Fuess, Isolated versus Condensed Anion Structure VI: X-ray Structure Analysis and 81Br NQR of Guanidinium Pentabromodicadmate(II), [C(NH2)3]Cd2Br5, tris-Hydrazinium Pentabromocadmate(II),
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ACCEPTED MANUSCRIPT [H2NNH3]3CdBr5, and bis-Hydrazinium Tetrabromocadmate(II)-Tetra Hydrate, [H2NNH3]2CdBr4-4H20, Z. Naturforsch., 55a, (2000) 390-396. [11] CrysAlis CCD and CrysAlis Red 1.171.38.41, Rigaku Oxford Diffraction, 2015. [12] G.M. Sheldrick, SHELXS97, Programs for Crystal Structures Solution and Refinement, University of Göttingen, Göttingen, Germany, 1997.
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[13] G.M. Sheldrick, Crystal structure refinement with SHELXL, Acta Cryst. C71, (2015) 3-8. doi: 10.1107/S2053229614024218 [14] K. Brandenburg, H. Putz, DIAMOND Version 3.0, Crystal Impact GbR, Bonn, Germany, (2006).
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[15] K. Aizu, Possible Species of “Ferroelastic” Crystals and of Simultaneously Ferroelectric and Ferroelastic Crystals, J. Phys. Soc. Jpn. 27, (1969) 387-396. doi.org/10.1143/JPSJ.27.387
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[16] J. Sapriel, Domain-wall orientations in ferroelastics, Phys. Rev. B 12, (1975) 5128-5140. doi.org/10.1103/PhysRevB.12.5128
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S0022-3697(18)31632-9
DOI:
10.1016/j.jpcs.2018.09.005
Reference:
PCS 8718
To appear in:
Journal of Physics and Chemistry of Solids
Received Date: 16 June 2018 Revised Date:
22 August 2018
Accepted Date: 6 September 2018
Please cite this article as: Z. Czapla, J. Janczak, O. Czupiński, J. Przesławski, M. Crofton, Structural phase transition and ferroelasticity in (H2NNH3)3CdBr5 crystal, Journal of Physics and Chemistry of Solids (2018), doi: 10.1016/j.jpcs.2018.09.005. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT
Structural phase transition and ferroelasticity in (H2NNH3)3CdBr5 crystal Z. Czapla1, J. Janczak2, O. Czupiński3, J. Przesławski4∗, M. Crofton4 1
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Department of Physics, Opole University of Technology, Ozimska 75, 45-370 Opole, Poland 2 Institute of Low Temperature and Structure Research, Polish Academy of Sciences, Okólna 2, 50-422 Wrocław, Poland 3 Faculty of Chemistry, University of Wrocław, F. Joliot-Curie 14, 50-383 Wrocław, Poland 4 Institute of Experimental Physics, University of Wrocław, Max Born Sq. 9, 50-204 Wrocław, Poland
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Abstract
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Single crystals of (H2NNH3)3CdBr5 were grown and their properties were investigated. DSC, DTG, structural studies, optical polarized microscopy observations and dielectric studies are presented. TGA showed the stability of the substance up to about 455 K and decomposition above this temperature. DSC studies revealed the first order structural phase transitions at 294/292 on heating/cooling runs. X-ray structural studies showed a change of symmetry from orthorhombic to monoclinic and the transition seems to belong to the mmmF2/m Aizu’s species. In optical studies performed with a polarizing microscope, the ferroelastic type of domain structure and the phase front appearance were observed. Dielectric measurements clearly evidenced the first-order phase transition as a jump-like decrease of permittivity on cooling and increase on heating. Structural and dielectric studies indicate the order-disorder character of the phase transition.
• • • •
∗
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Highlights:
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Keywords: organic – inorganic compounds; structural studies, phase transitions; DSC, DTA, DTG measurements; dielectric properties, optical observations;
Examination of the structural phase transition in the (H2NNH3)3CdBr5 was performed The transition proceeds between two centrosymmetric groups Cmcm ↔ P21/m The transition is of the first order and has the order – disorder character
Ferroelastic domain structure is typical for the mmmF2/m of the Aizu`s species
Corresponding author: [email protected]
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ACCEPTED MANUSCRIPT 1. Introduction Cadmium chloride and bromide form a large family of hybrid organic-inorganic compounds containing various anionic sublattices. Interesting structures and phase transitions were found
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in perovskite type compounds containing different amine cations. Halogenocadmate compounds form various structural architectures from which crystals with desired physical properties can be obtained [1,2]. Taking into account the role of cadmium in biological processes [3], compounds of this metal are an interesting subject of study. Among them one mention
[(CH2)3(NH3)2]CdCl4
[4,5],
[(CH2)3(NH3)2]CdBr4
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can
[6,7]
and
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[(CH3)2CHNH3)]4Cd3Cl10 [8,9] with a polymer anionic structure that exhibits structural phase transitions. Interesting structures of cadmium compounds were determined in the case of salts with hydrazinium and guanidinium cations [10]. The (H2NNH3)3CdBr5 (tris-hydrazinium pentabromocadmate (II)) and the [C(NH2)3]Cd2Br5 (guanidinium pentabromodicadmate (II) show anionic sublattices of perovskite type and on the basis of NQR [10] and DSC studies
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exhibit structural phase transitions. In the case of the inorganic (H2NNH3)3CdBr5 compound two structural first-order phase transitions were noticed in DSC, namely: at about 445 K and
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294 K. At about 450 K, melting of the substance was observed with consequent decomposition. In NQR studies the transition was reported at 304 K, corresponding to that
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seen at 294 K in DSC. On the ground of X-ray studies the crystal was proposed to crystallize in the polar space group P21 [10] at 300 K and this symmetry was elucidated for the low temperature phase. Above the phase transition the symmetry was assumed to be P21/m [10]. The proposed change of symmetry is typical for ferroelectric phase transitions. Thus, it is suggested that the transition observed in (H2NNH3)3CdBr5 should be that of a paraelectricferroelectric one. However, it is doubtful that the symmetry found at 300 K is the symmetry of the low temperature phase. The structure studied at 300 K can be related to the phase existing above
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ACCEPTED MANUSCRIPT 294 K. To describe the phase transition and properties of the crystal we decided to grow single crystals of this substance, and aimed to study the character of the phase transition and its properties in some temperature range around the phase transition at about 294 K, where
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ferroelectricity is expected.
2. Experimental 2.1. Preparation.
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Polycrystals were obtained from a water solution of stoichiometric quantities of hydrazinium bromide, cadmium bromide CdBr2·2H2O and a small excess of hydrobromic acid. Thin
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needle-like crystals were obtained after slow evaporation at room temperature. These crystals were dissolved in water with a small excess of hydrobromic acid and then the solution was evaporated at a constant temperature of 305 K. After evaporation thicker needles were chosen as germs for the growth of single crystals. Using the selected germs the single crystals were
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grown from the saturated solution at a constant temperature of 305 K. The crystals elongated along the a-axis (2-3 cm) with an area perpendicular to the a-axis of 4 x 6 mm2 and were obtained during 4-5 weeks. This allowed us to prepare plates of area 10-15 mm2 and thickness
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of about 0.5-0.7 mm for dielectric and optical studies. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) were carried out
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by means of a Seteram SETSYS 16/18 instrument in the temperature range 295 – 780 K on a heating run at a rate of 2 K/min. The heat flow studies were performed using a Perkin-Elmer 8500 differential scanning calorimetry (DSC) at heating-cooling rates of 20 and 10 K/min in the temperature range 120 – 350 K, respectively.
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ACCEPTED MANUSCRIPT 2.2. Single crystal X-ray data collection. X-ray diffraction (intensity) data for the crystal were collected using graphite monochromatic MoKα radiation on a four-circle κ geometry KUMA KM-4 diffractometer with a twodimensional area CCD detector at 310(1), 296(1) and 278(1) K. The ω-scan technique with
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∆ω = 1.0º for each image was used for data collection. The unit cell parameters were refined by the least-squares method on the basis of all measured reflections. One image was used as a standard after every 40 images for monitoring of the crystal stability and data collection, and
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no correction on the relative intensity variations was necessary. Data collection was made using the CrysAlis CCD program [11]. Integration, scaling of the reflections, correction for
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Lorenz and polarisation effects and absorption corrections were performed using the CrysAlis Red program [11]. The structure at 310(1) and 296(1) K was solved by direct methods using SHELXS [12] and refined using SHELXL-2014 programs [13]. The hydrogen atoms were not localised. The final difference Fourier maps showed no peaks of chemical significance.
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Obtaining the structure solution at 278(1) was unsuccessful due to the crystal twinning. Details of the data collection parameters, crystallographic data and final agreement parameters are collected in Table 1. Selected geometrical parameters are listed in Table 2.
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Visualisation of the structure was made with the Diamond 3.0 program [14].
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2.3. Physical studies.
Optical observations were done by means of a polarizing microscope in the temperature range 280 – 320 K on cooling and heating runs. The samples were placed in an LINKAM THM-600 heating/cooling stage. For microscopic observations thin crystalline plates were used. The rate of cooling/heating close to the phase transition temperature was 0.2 K / min. Dielectric measurements were performed with a HP computer controlled system at a frequency of 1 kHz and a temperature range of 250 - 320 K on a cooling/heating run along three crystallographic axes. Silver paste was used as electrodes.
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ACCEPTED MANUSCRIPT 3. Results of experimental measurements and discussion 3.1. Crystals Transparent single crystals in the shape of long rods were of good quality for dielectric studies and optical observations. A habit of the crystal resembles clearly orthorhombic symmetry.
experimental studies. 3.2. DTA and TGA studies
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Results of DTA and TGA studies are presented in Fig. 1.
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However, the crystals are very fragile, break easily and it was difficult to prepare samples for
Fig. 1. Temperature dependence of the DTA and TGA signals for the (H2NNH3)3CdBr5 crystal.
The TGA studies showed thermal stability up to 454 K, however in the vicinity of this temperature a double anomaly on the DTA curve is observed. It is most likely the structural 5
ACCEPTED MANUSCRIPT phase transition followed by melting and decomposition of the substance. This situation was pointed out in [10].
3.2. DSC studies
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Looking at the DTA and TGA studies we decided to study the transition at 294 K where ferroelectricity is expected. The heat flow observed in the DSC studies is presented in Fig. 2.
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The studies were done around the phase transition predetermined at 294 K [10].
Fig. 2. Heat flow as a function of temperature for (H2NNH3)3CdBr5
As can be clearly seen, the anomaly observed indicates a first order phase transition. The transition is fully reversible and temperature hysteresis is about 2 K, as deduced from the 6
ACCEPTED MANUSCRIPT onset anomalies presented above. The transition enthalpy and entropy are equal to 1.7 kJ/mol and 5.8 J/molK, respectively. Both temperature and thermal quantities are in agreement with those presented in [10]. The entropy change is approximately equal to Rln2 and indicates the
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order-disorder character of the phase transition.
3.3. Description of structure
To describe the phase transition the structure of the crystal was studied. Taking into account
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basic crystallographic data are presented in Table 1.
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the appearance of a structural phase transition we checked the symmetry of both phases. The
Table 1. Crystal data for two phases for (H2NNH3)3CdBr5 Temperature (K)
310
Empirical formula
CdBr5H15N6 orthorhombic
278
CdBr5H15N6
CdBr5H15N6
orthorhombic
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Crystal system
296
monoclinic
Cmcm
Cmcm
P21/m
a (Å)
11.8642(6)
11.8618(4)
11.7423(8)
b (Å)
14.6580(8)
14.6859(5)
14.7430(16)
7.7933(5)
7.8062(3)
15.5944(30)
90.0
90.0
89.821(14)
90.0
90.0
90.00
90.0
90.0
90.00
V (Å3)
1355.30(13)
1359.85(8)
2699.65(14)
Z
4
4
8
µ (mm–1)
16.323
16.323
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Space group
α (0) β(0) γ(0)
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c (Å)
Crystal size (mm)
0.28 × 0.26 × 0.22
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ACCEPTED MANUSCRIPT Radiation type, λ (Å) θ range(o)
Mo Kα, 0.71073 3.418-27.864
3.423-29.482
Structural analysis showed orthorhombic symmetry of the (H2NNH3)3CdBr5 crystal at 310 K
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and 296 K and the space group Cmcm (point group mmm). The molecular structure at 310 K and 296 K is almost the same and is illustrated in Figs. 3 and 4. An asymmetric unit of (H2NNH3)3CdBr5 consists of half of a distorted CdBr6 octahedron (Table 2) and one and a
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half NH2NH3+ cations. Both hydrazinium cations are disordered, however in one, the nitrogen atom (N1) is shared between both orientations, whereas in the second hydrazinium cation
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both nitrogen atoms (N3 and N4) statistically occupy two positions (see Fig. 4). Each distorted CdBr6 octahedron has two shared Br atoms with its neighbours forming a onedimensional zig-zag coordination polymer {CdBr5}n along the c-axis. Although the hydrogen atoms of the disordered hydrazinium cations were not localized, the hydrazinium cations
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interact with each other via NH…N hydrogen bonds forming chains along the c-axis, since the N…N distances within the chain are 2.945(7) Å {N2…N3}, 2.924(12) Å {N3…N3#, (#) x, -
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y, -z) and 3.004(13) Å {N4…N4#; symmetry code (#) x, -y, -z}.
Fig. 3. View of molecular structure of (H2NNH3)3CdBr5 (symmetry code: (i) 1-x, 1-y, 0.5+z; (ii) x, y, 0.5-z; (iii) 1-x, y, 0.5-z).
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Fig. 4. Molecular packing of (H2NNH3)3CdBr5 showing the zig-zag coordination polymer of
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{CdBr5}n and disordered NH2NH3+ cations viewed along a-axis.
Table 2. Selected geometrical parameters for (H2NNH3)3CdBr5.
CdBr1 x2
310(1)K
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Temperature
296(1)K
2.8358(4)
2.8420 (3)
2.6793(7)
2.6828 (6)
CdBr3 x2
2.7491(6)
2.7498 (5)
N1—N2
1.213(4)
1.227 (4)
N3—N4
1.212(5)
1.209 (5)
Br1—Cd1—Br3
86.070(15)
86.011 (12)
Br2—Cd1—Br3
93.669(13)
93.711 (10)
Br2i—Cd1—Br3
93.669 (13)
93.711 (10)
Br2—Cd1—Br2i
94.59(3)
94.86 (3)
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CdBr2 x2
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ACCEPTED MANUSCRIPT Br1iii—Cd1—Br1
86.795(15)
86.736 (12)
Br2—Cd1—Br1iii
176.10(2)
175.938 (18)
Symmetry code: : (i) 1-x, 1-y, 0.5+z; (ii) x, y, 0.5-z; (iii) 1-x, y, 0.5-z.
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Structural studies at 278 K (below the phase transition temperature) showed a monoclinic structure. However, strong twinning (below the phase transition temperature) prevented the determination of a detailed crystallographic structure at the low temperature phase. Taking
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into account the change of symmetry from orthorhombic to monoclinic phase it is expected that the observed twinning is connected with a phase transition of the ferroelastic type. The
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presence of a symmetry center in both phases excludes the ferroelectricity. Considering the entropy change at the phase transition, and in spite of lack of the detailed structure of the low temperature phase, the molecular mechanism of the transition is expected to be connected
3.4. Optical studies
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with the ordering of hydrazinium cations.
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Looking at the symmetry of the (H2NNH3)3CdBr5 crystal found at 296 K and below the phase transition temperature at 278 K, one can notice that the transition at TC occurs between the
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orthorhombic and monoclinic phases and one deals with the symmetry change Cmcm ↔ P21/m. Thus, the transition is expected to be of ferroelastic type. According to Aizu’s notation [15] the transition can be classified as the mmmF2/m species with two orientation states below the phase transition temperature. Polarizing microscopy observations of the crystal along the a-axis revealed the appearance of a domain structure of ferroelastic type with domain walls in the (010) and (001) planes below 294 K [16]. The notation of the planes is indexed with respect to the orthorhombic axes. The observed domain structure presented in Fig. 5 confirms the transition mmmF2/m. 1
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Fig. 5. The ferroelastic domain structure observed for the a-cut of the (H2NNH3)3CdBr5 crystal (T = 285 K).
3.5. Dielectric studies
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Results of dielectric measurements performed at a frequency of 1 kHz along three
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crystallographic directions are presented in Fig. 6.
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Fig. 6. a) Temperature dependence of the dielectric permittivity measured along the a-axis.
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Fig. 6. b) Temperature dependence of the dielectric permittivity measured along the b-axis.
Fig. 6. c) Temperature dependence of the dielectric permittivity measured along the c-axis.
Heating and cooling around the phase transition temperature showed an anomalous jump-like decrease of permittivity on cooling and an increase on heating, in addition to temperature
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ACCEPTED MANUSCRIPT hysteresis. This is characteristic for a first-order transition. The increase of the dielectric permittivity on heating is connected with the order-disorder mechanism of the transition.
4. Summary
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From the studies presented one can summarize as follows: 1. DSC data revealed the reversible first-order phase transition at 294/292 K on heating and cooling, respectively;
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2. structural X-ray investigations showed the change of symmetry from orthorhombic above the phase transition to monoclinic below the phase transition temperature,
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Cmcm ↔ P21/m;
3. structural studies and optical observations indicate that the phase transition is of ferroelastic type and can be classified as mmmF2/m Aizu’s species; 4. the molecular mechanism of the transition is expected to be connected with the ordering of hydrazinium cations;
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5. dielectric permittivity exhibits jump-like and hysteretic behavior characteristic for the
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first order transition.
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. Supplementary material
Additional material comprising full details of the X-ray data collection and final refinement parameters including anisotropic thermal parameters and a full list of the bond lengths and angles have been deposited with the Cambridge Crystallographic Data Center in the CIF format as supplementary publications no. CCDC 1845071 and 1845072 for 296 and 310 K. Copies of the data can be obtained free of charge on the application to CCDC, 12 Union Road, Cambridge, CB21EZ, UK, (fax: (+44)1223-336-033; email: [email protected] ).
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ACCEPTED MANUSCRIPT References: [1] Ch.E. Costin-Hogan, E. Chen, Ch.-L. Hughes, A. Pickett, R. Valencia, N.P. Rath, A. Beaty, “Reverse engineering: Toward 0-D cadmium halide clusters, CrystEngComm 10 (2008) 1910-1915. http://dx.doi.org/10.1039/B812504J
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[2] A. Thorn, R. Willet, B. Twamley, Retro-Crystal Engineering Analysis of Two NMethylethylenediammonium Cadmium Halide Salts Obtained by Dimensional Reduction and Recombination of the Hexagonal CdX2 Lattice, Cryst. Growth Des. 5 (2005) 673-679. doi:10.1021/cg030059s
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[3] L.G. Marzili, T.J. Kistenmacher, G.I. Eichhorn, Metal ions, in Biology, T.G. Spiro (Ed.) vol.1, Wiley, New York, 1980, p. 179. (104. Marzilli LG, Kistenmacher TJ, Eichhorn GL. Structural principles of metal ion-nucleotide and metal ion-nucleic acid interactions. In: TG Spiro, ed. Nucleic acid-metal ion interactions. New York, NY: John Wiley & Sons, Inc.; 1980.)
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[4] R. Kind, S. Plesko, P. Gauter, J. Ross and J. Fousek, Structural phase transitions in the perovskite-type layer compounds NH3(CH2)3NH3CdCl4, NH3(CH2)4NH3MnCl4, and NH3(CH2)5NH3CdCl4,Phys.Rev. B 23 (1981) 5301-5315. doi.org/10.1103/PhysRevB.23.5301 [5] B. Staśkiewicz, I. Turowska-Tyrk, J. Baran, Cz. Górecki and Z. Czapla, Structural characterization, thermal, vibrational properties and molecular motions in perovskite-type diaminopropanetetrachlorocadmate NH3(CH2)3NH3CdCl4 crystal, J. Phys. Chem. Sol., 75, 12 (2014)1305-1317. doi.org/10.1016/j.jpcs.2014.07.004
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[6] H. Ishihara, S. Dou, K. Horiuchi, V.G. Krishnan, H. Paulus, H. Fuess, A. Weiss, Isolated versus Condensed Anion Structure II; the Influence of the Cations (1,3-propanediammonium, 1,4-phenylendiammonium, and n-propylammonium) on Structures and Phase Transitions of CdBr2-4Salts A 79,81Br NQR and X-ray Structure Analysis, Z. Naturforschung 51a, (1996) 1216-1228. https://doi.org/10.1515/zna-1996-1212
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[7] B. Staśkiewicz, O. Czupiński and Z. Czapla, On some spectroscopic properties of a layered 1,3-diammoniumpropylene tetrabromocadmate hybrid crystal, J. Mol. Struct., 1074, (2014) 723-731. doi.org/10.1016/j.molstruc.2014.05.036 [8] A. Gągor, A. Waśkowska, Z. Czapla and S. Dacko, Structural phase transitions in tetra(isopropylammonium) decachlorotricadmate(II), [(CH3)2CHNH3]4Cd3Cl10, crystal with a two-dimensional cadmium(II) halide network. Acta Cryst. B 67, (2011). 122-129. doi:10.1107/S0108768110054583 [9] B. Staśkiewicz, S. Dacko and Z. Czapla, Successive phase transitions in tetra(isopropylamine)decachlorotricadmate (II) [(CH3)2CHNH3]4Cd3Cl10 crystal - Dielectric and dilatometric studies., Curr. Appl. Phys., 12 (2) (2012) 413-417. doi:10.1016/j.cap.2011.07.039 [10] H. Ishihara, K. Horiuchi, V.G. Krishnan, I. Svoboda, H.Fuess, Isolated versus Condensed Anion Structure VI: X-ray Structure Analysis and 81Br NQR of Guanidinium Pentabromodicadmate(II), [C(NH2)3]Cd2Br5, tris-Hydrazinium Pentabromocadmate(II),
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ACCEPTED MANUSCRIPT [H2NNH3]3CdBr5, and bis-Hydrazinium Tetrabromocadmate(II)-Tetra Hydrate, [H2NNH3]2CdBr4-4H20, Z. Naturforsch., 55a, (2000) 390-396. [11] CrysAlis CCD and CrysAlis Red 1.171.38.41, Rigaku Oxford Diffraction, 2015. [12] G.M. Sheldrick, SHELXS97, Programs for Crystal Structures Solution and Refinement, University of Göttingen, Göttingen, Germany, 1997.
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[13] G.M. Sheldrick, Crystal structure refinement with SHELXL, Acta Cryst. C71, (2015) 3-8. doi: 10.1107/S2053229614024218 [14] K. Brandenburg, H. Putz, DIAMOND Version 3.0, Crystal Impact GbR, Bonn, Germany, (2006).
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[15] K. Aizu, Possible Species of “Ferroelastic” Crystals and of Simultaneously Ferroelectric and Ferroelastic Crystals, J. Phys. Soc. Jpn. 27, (1969) 387-396. doi.org/10.1143/JPSJ.27.387
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[16] J. Sapriel, Domain-wall orientations in ferroelastics, Phys. Rev. B 12, (1975) 5128-5140. doi.org/10.1103/PhysRevB.12.5128
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