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The family of known guanylurea(1+) sulphates was extended for two novel triclinic (space group P-1) members - bis(guanylurea(1+)) sulphate dihydrate and tetrakis(guanylurea(1+)) bis(hydrogen sulphate) sulphate. Additionally, the monoclinic (space group P21/n) guanylurea(1+) hydrogen selenate was also isolated and characterised. Besides of X-ray diffraction study these novel guanylurea chalcogenates were studied by the methods of vibrational spectroscopy. The study of thermal behaviour of the prepared salts revealed reversible λ-shaped anomaly for tetrakis(guanylurea(1+)) bis(hydrogen sulphate) sulphate at 354 K. This effect was studied in detail by the combination of DSC and temperature-dependent IR and Raman spectroscopies.

Three polymorphic modifications of bis(N-phenylbiguanidium(1+)) oxalate are reported, and their characterization is discussed in this paper. The non-centrosymmetric bis(N-phenylbiguanidium(1+)) oxalate (I), which was obtained from an aqueous solution at 313K, belongs to the monoclinic space group Cc (a=6.2560(2)Å, b=18.6920(3)Å, c=18.2980(5)Å, β=96.249(1)°, V=2127.0(1)Å(3), Z=4, R=0.0314 for 4738 observed reflections). The centrosymmetric bis(N-phenylbiguanidium(1+)) oxalate (II) was obtained from an aqueous solution at 298K and belongs to the monoclinic space group P21/n (a=6.1335(3)Å, b=11.7862(6)Å, c=14.5962(8)Å, β=95.728(2)°, V=1049.90(9)Å(3), Z=4, R=0.0420 for 2396 observed reflections). The cooling of the centrosymmetric phase (II) leads to the formation of bis(N-phenylbiguanidium(1+)) oxalate (III) (a=6.1083(2)Å, b=11.3178(5)Å, c=14.9947(5)Å, β=93.151(2)°, V=1035.05(8)Å(3), Z=4, R=0.0345 for 2367 observed reflections and a temperature of 110K), which also belongs to the monoclinic space group P21/n. The crystal structures of the three characterized phases are generally based on layers of isolated N-phenylbiguanidium(1+) cations separated by oxalate anions and interconnected with them by several types of N-H(...)O hydrogen bonds. The observed phases generally differ not only in their crystal packing but also in the lengths and characteristics of their hydrogen bonds. The thermal behaviour of the prepared compounds was studied using the DSC method in the temperature range from 90K up to a temperature near the melting point of each crystal. The bis(N-phenylbiguanidium(1+)) oxalate (II) crystals exhibit weak reversible thermal effects on the DSC curve at 147K (heating run). Further investigation of this effect, which was assigned to the isostructural phase transformation, was performed using FTIR, Raman spectroscopy and X-ray diffraction analysis in a wide temperature range.

The inorganic-organic hybrid compound [Cu(en)2(VO3)2]•3H2O (1) was prepared by crystallization at room temperature from the CuSO4•5H2O – KVO3 – ethylenediamine – H2O system. Upon cooling 1, phase transition occurred at 176 K. Single-crystal diffraction analysis of the high- temperature and low-temperature phases has shown both phases to be polymeric, incorporating metavanadate chains (VO3)nn– coordinated via oxygen atoms to copper(II) atoms. The four remaining positions of the copper atoms with octahedral environment are taken by nitrogen atoms of two ethylenediamine ligands. The low-temperature phase exhibits displacive modulation in its structure. The band gap of the high-temperature phase is 2.95 eV. The compound is paramagnetic (1.79 µB) and exhibits no distinct magnetic interactions. A detailed phase analysis upon heating of 1 to 600 °C revealed the final products of the thermal decomposition to be monoclinic Cu(VO3)2, Cu2V2O7 as ziessite and V2O5. After cooling to room temperature, monoclinic Cu(VO3)2 transformed to its triclinic polymorph, while ziessite became transformed to blossite.

BaTiO3 films deposited onto TiNb and Ti substrates using hydrothermal synthesis method were studied in the presented work. These films are supposed to improve properties of bone implants due to their ferroelectric behaviour, because ferroelectrics induce improved bone formation. A great question is the chemical stability of the used material. It can be crucial for its biocompatibility and possible in vivo application. We studied chemical composition of prepared samples, especially concentration of Ba and Ti and trends of these concentrations stimulated by a solution saline action. The Ba and Ti concentrations were determined by XPS under ultra - high vacuum condition. The BaTiO3 films were investigated as received after the preparation procedure as well as after a long - time treatment in solution saline. Every sample was introduced to the solution saline at first for 1 and later for 3 weeks. Ti concentration almost does not change during our experiments while a meaningful Ba decrease is observed. Nevertheless, barium release seems to slow down with respect to the time of solution saline action. Stability of barium titanate films in a period of several months and an absolute amount of the released barium will be a subject of the next research.

The broadband dielectric response of the uniaxial ferroelectric strontium barium niobate with 35% Sr has been studied from 1 kHz to 30 THz along the polar $c$ axis using high-frequency and low-frequency dielectric spectroscopies, time-domain terahertz spectroscopy, and far-infrared reflectivity, in the wide temperature interval 20--600 K. The mechanisms that contribute to the ferroelectric phase transition and to the dielectric anomaly in this material are the softening of an anharmonic excitation in the THz range related to cation hopping and the slowing down of a relaxation in the GHz range, which saturates below ${T}_{\mathrm{C}}$ near 1 MHz. In the ferroelectric phase, a relaxation, related to domain-wall dynamics, appears in the sub-GHz range and hardens on cooling up to 10 GHz. The ferroelectric-paraelectric transition, investigated by electron diffraction, has been assessed to the appearance of a supplementary mirror plane perpendicular to the polar axis.

Four novel organic salts of 3,5-diamino-1,2,4-triazole (guanazole) with malonic, glutaric, adipic and L -malic acids have been prepared and X-ray structural analyses have been performed within our project focused on the preparation of new non-linear optical materials. The salts guanazolium(1+) hydrogen adipate and guanazolium(1+) hydrogen L -malate crystallize in the non-centrosymmetric space groups of monoclinic ( Cc ) and orthorhombic systems ( P 2 1 2 1 2 1 ), respectively. Unfortunately, the remaining two salts guanazolium(1+) hydrogen malonate and guanazolium(1+) hydrogen glutarate belong to the centrosymmetric space group P -1 of the triclinic system. All salts were also characterized by the methods of vibrational spectroscopy (FTIR and FT Raman). The interpretation of the vibrational spectra is based on our previous ab initio calculations. The second harmonic generation’s quantitative measurements of powdered samples at 800 nm and 1064 nm were performed. The thermal behavior of the prepared compounds was studied by the DSC method in the temperature interval from 90 K up to a temperature close to the melting points of the crystals.

In this study, ceramic samples of lead zirconate titanate Pb(Zr0.42Ti0.58)O3 (PZT 42/58) doped with Fe (hard) and Nb (soft) were studied by Raman, infrared (IR) and THz spectroscopy in the temperature range from 900 to 20 K. From the evaluation of the IR and Raman phonons in undoped ceramics, we conclude that tetragonal PZT ceramics undergo a low-temperature phase transition to a tilted phase, revealed by anomalies in phonon parameters and the appearance of new modes. Doped samples also presented similar behaviour. The main differences between undoped and doped ceramics lie in the dielectric behaviour below phonon frequency range, where several mechanisms appear: a soft central mode (CM) located near 1 THz and two relaxations in the GHz range. Both types of doping raise the permittivity values below the phonon frequencies, not only increasing the dielectric contribution of the CM, but also modifying the dielectric response near the GHz range. Soft ceramics show higher permittivity with logarithmic increas...

Three organic salts of biguanide with oxalic, succinic and l -tartaric acids have been prepared and X-ray structural analysis has been performed. Biguanidium(1+) oxalate hemihydrate (a = 6.8330(2) A, b = 10.0430(2) A, c = 14.6230(4) A, α = 90.236(1) , β = 90.333(1) , γ = 105.605(2) , V = 966.46(4) A3, Z = 1, R = 0.0393 for 3704 observed reflections) and biguanidium(1+) hydrogen succinate (a = 6.4600(1) A, b = 6.7670(2) A, c = 11.4150(3) A, α = 91.822(1) , β = 105.312(1) , γ = 90.922(1) , V = 480.89(2) A3, Z = 2, R = 0.0357 for 1880 observed reflections) belong to the triclinic space group P 1 ¯ . Their crystal structures are based on biguanidium(1+) pairs connected by intermolecular N–H⋯N hydrogen bonds. The remaining ions (eventually water molecules) form a 3D structural network with these pairs. Furthermore, the formation of the cationic and anionic layers interconnected by intermolecular N–H⋯O hydrogen bonds was observed in the crystal structure of biguanidium(1+) hydrogen succinate. Biguanidium(2+) l -tartrate crystallizes in the orthorhombic space group P 212121 (a = 6.7170(2) A, b = 9.2740(2) A, c = 16.1500(4) A, V = 1006.04(4) A3, Z = 4, R = 0.0432 for 2193 observed reflections). The crystal structure is based on l -tartrate chains, which are interconnected by isolated biguanidium(2+) cations via several types of N–H⋯O hydrogen bonds. The formation of l -tartrate chains is mediated by two types of intermolecular O–H⋯O hydrogen bonds connecting the hydroxyl and carboxylate groups. The FTIR and FT Raman spectra of all the compounds were recorded and discussed. The theoretical values of the first hyperpolarizability components were calculated for biguanidium(1+) and biguanidium(2+) cations at the B3LYP level with the 6-311G(d,p) basis set. Quantitative measurements of the second harmonic generation of powdered biguanidium(2+) l -tartrate at 800 nm were performed and a relative efficiency of 2% (compared to KDP) was observed. The thermal behaviour of all the prepared compounds was studied by the DSC method in the temperature interval from 90 K up to a temperature close to the melting points of the crystals. The FTIR and FT Raman spectra of biguanidium(2+) l -tartrate were investigated down to 130 K.

Aminoguanidinium(1+) hydrogen l -tartrate monohydrate was prepared by crystallisation from aqueous solution and X-ray structural analysis was carried out. The substance crystallises in the orthorhombic system in space group P 2 1 2 1 2 1 , a = 7.1380(2) A, b = 9.9700(4) A, c = 14.0790(6) A, V = 1001.94(7) A 3 , Z = 4, R = 0.0271 for 2272 observed reflections. The crystal structure consists of a 3D framework formed by hydrogen tartrate anions and water molecules with incorporated aminoguanidinium(1+) cations connected by a system of hydrogen bonds. The FTIR and FT Raman spectra of natural and N,O-deuterated compounds were measured and discussed at laboratory temperature. DSC measurements were carried out in the temperature range from 95 to 380 K. A weak anomaly was observed at a temperature of 268 K. Quantitative measurements of second harmonic generation of powdered aminoguanidinium(1+) hydrogen tartrate monohydrate at 800 nm were performed relative to KDP and a relative efficiency of 14% was observed.

Piperidinium nitrate was studied by FTIR and FT Raman spectroscopy in the range 100-4000 cm-1 at 300 K. On the basis of DSC measurements which exhibit two effects indicating phase transition at 256 and 295 K, FTIR spectra were recorded down to a temperature of 90 K. Discussion of the phase transition mechanism is based on the observed changes in the FTIR spectra during cooling of the compound.

Potassium tantalum niobate (KTa x Nb 1− x O 3 , (KTN), where x = 0, 0.21, 0.36, 0.53, 0.74, 0.82, 0.86, and 1) thin films were prepared by chemical solution deposition (CSD) on Si substrates. A homogeneous and stable sol was obtained by dissolving potassium, niobium and tantalum isobutoxides in absolute isobutanol, refluxing for 30 min and adding diethanolamine as a modifier. The sol was deposited by spin coating. KTN perovskite films were successfully prepared only on substrates covered with Al 2 O 3 “chemical” and KNbO 3 seeding buffer layers, otherwise a pyrochlore structure was preferred. Annealing temperature and heating regime were also important factors for film quality. The powder X-ray diffraction confirmed that the prepared films had pseudocubic perovskite structure. The infrared transmittance spectrum of the films for high concentration of Ta shows three minima corresponding to optical active phonons in the perovskite crystal structure. Their positions are in agreement with those for the bulk m...

Potassium tantalate KTaO3, (KT) thin films of perovskite structure were prepared by chemical solution deposition (CSD) on Si and SiO2 glass substrates. Potassium and tantalum isobutoxides were dissolved in absolute isobutanol with an addition of diethanolamine as a modifier to obtain a homogeneous and stable precursor solution. Optimum conditions for film preparation were found. Annealing temperature and heating regime, Al2O3 “chemical” buffer layer and KNbO3 seeding layer were the determining factors of the film quality. It was demonstrated by X-ray diffraction (XRD) that the films have the desired cubic perovskite structure. The infrared transmittance spectrum of the films shows three minima corresponding to optical active phonons in the perovskite crystal structure. Their positions are in agreement with the bulk material, except the 14 cm−1 shift of the lowest phonon, which has been also observed in other perovskite materials. The temperature dependence of the phonon parameters has been studied too.

Potassium tantalate niobate (KTaxNb1−xO3, (KTN), where x = 0, 0.21, 0.36, 0.53, 0.74, 0.82, 0.86, and 1) thin films of perovskite structure were prepared by chemical solution deposition (CSD) on Si and SiO2 glass substrates. A homogeneous and stable precursor solution was obtained by dissolving potassium, niobium and tantalum isobutoxides in absolute isobutanol and an addition of diethanolamine as a modifier. The film quality was determined by annealing temperature and heating regime, Al2O3 “chemical” buffer layer and KNbO3 seeding layer. Optimum conditions for film preparation were found. It was approved by X-ray diffraction (XRD) that the films have the wanted pseudocubic perovskite structure. Infrared transmittance was measured for broad range of Ta/Nb ratios. The spectra show continuous transformation from KTaO3 to KNbO3 and indicate that the optical axis lies in the plane of the film.

A phase transition was found to occur at approximately 153 K in the title compound, (C8H20N)2[PdCl6]. The structures of the two phases are reported at 292 and 130 K. The low-temperature phase is twinned. The phase transition is accompanied by a minor displacement of the ions. There are C-H...Cl interactions as short as approximately 2.80 A, indicating the existence of hydrogen bonds, and this was confirmed by vibrational spectroscopy. The [Pd2Cl6]2- anion occupies sites of mmm and 2/m symmetry in the room-temperature and low-temperature phases, respectively.

A series of SiO2/KHSO4 nanocomposites with various SiO2/salt ratios was prepared where the active compound was added before gelation. The sol was prepared by mixing of these hydrogen salts, TEOS (tetraethyl orthosilicate) and water. After gelation and heat treatment (heating slowly to 200–220°C under vacuum), the samples were characterized by X-ray diffraction, Differential Scanning Calorimetry (DSC), IR spectroscopy, Scanning Electron Microscopy (SEM), and High Resolution Transition Electron Microscopy (HR TEM). DSC measurements showed phase transition temperature shifts that depended on the SiO2/salt ratio. The properties of the nanocomposite samples were compared with the bulk materials. The shift in the phase transitions to lower temperatures was attributed to the particle size effect.

New series of chiral liquid crystalline compounds, (S)-[4-n-alkyloxy-benzoyloxyphenyl]-4′-[(2-n-alkyloxy)propionyloxy]benzoate (QMn/m), were synthesised. Polymorphism of the new compounds was investigated by polarising microscopy and differential scanning calorimetry. All members of the homologous series showed enantiotropic SmC* and N* mesophases except one compound having the longest alkyl chain in both terminal groups. The spontaneous polarisation of these ferroelectric liquid crystalline compounds is about 110–130 nC/cm2. The temperature dependence of the dielectric permittivity was measured for all the compounds studied. Several ferroelectric binary mixtures were prepared in order to get a wide enantiotropic chiral SmC* phase at ambient temperature.

Four new chiral homologous series of ferroelectric liquid crystals S-(-)-4-(2-n-alkoxy-propionyloxy)biphenyl-4′-n-alkoxy-3,5-dimethylbenzoate (DMn/m series) having O-substituted S-(-)-lactic acid as terminal group were synthesized, and characterized. They showed monotropic chiral smectic C and chiral nematic mesophases, and two representatives exhibited blue phase as well. Binary mixtures of these compounds were investigated. The effect of the lateral methyl substitutents and the length of the terminal groups on the chiral and non-chiral parts were investigated.

Physical properies of ion-conducting nanocomposites are reviewed. Special attention is paid to the change of the bulk characteristics of ionic salts in the nanocomposites due to the formation of the interface phases. The main thermodynamic reason of the formation of the nanocomposite as well as the stabilization of the interface phases is the adhesion energy σa. At sufficiently high σa values, the ionic salt tends to spread along the oxide surface, which leads to the formation of the nanocomposite on sintering. The adhesion is the result of the interface interaction and incorporates the stage of the specific adsorption of the interface ions. It leads to the formation of the double layer formed by the point defects in the interface region of the ionic salt. In the case of the strong adhesion, the structural reconstruction or the formation of the metastable interface phase takes place. Analysis of the experimental data shows that interface phases exist in composites AgI–Al2O3, MeNO3–Al2O3 (Me = Li, Na, K, Rb, and Cs), CsHSO4–SiO2, RbNO3–SiO2 and CsCl–Al2O3. Their structure may be either epitaxial crystalline, or amorphous. The thickness of the interface phase as estimated on the basis of the brick-wall model is about 3–4 nm.

AgI–Al2O3 nanocomposites are investigated by high-resolution electron microscopy and luminescence spectroscopy. The results show that both crystalline and amorphous phases coexist in AgI–Al2O3 composites. At sufficiently high alumina content, almost all AgI occurs as amorphous spherical nanoparticles distributed uniformly on alumina surfaces. The amorphous phase exhibits unusual luminescence spectra with a single, very broad nonstructured band. The amorphous phase is stabilized on AgI–alumina interfaces with the relative concentration progressively increasing with the Al2O3 fraction. The thickness of the interface amorphous layer adjacent to Al2O3 particles estimated by means of a simple brick-wall model is about 3 nm.

In the title compound, C2H7N4O+·BF4−, intermolecular N—H...O hydrogen bonds connect the cations into chains parallel to thecaxis, with graph-set motifC(4). These chains are in turn connected into a three-dimensional network by intermolecular N—H...F hydrogen bonds. The B—F distances distances in the anion are not equal.

Fourteen new structural phase transitions are detected in layer-type monoalkylammonium hexachloro-stannates (CnH2n+1NH3)2SnCl6 (n = 2 to 8) by means of differential scanning calorimetry. The basic thermodynamic data are determined for the transitions. The infrared spectra of the compounds are measured in the range of molecular vibrations (500 to 4000 cm−1) at room temperature and in dependence on temperature (77 to 298 K) by the method of nujol mull. Vierzehn neue strukturelle Phasenumwandlungen werden in geschichteten Monoalkylammonium-hexachlorostannaten (CnH2n+1NH3)2SnCl6 (n = 2 bis 8) mittels dynamischer Leistungs-Differenzkalorimetrie entdeckt. Es werden die thermodynamischen Grunddaten fur diese Umwandlungen ermittelt. Die Infrarotspektren dieser Verbindungen werden im Bereich der Molekulschwingungen (500 bis 4000 cm−1) bei Raumtemperatur und in Abhangigkeit von der Temperatur (77 bis 298 K.) mit Hilfe einer Nujolsuspension gemessen.

Two previously not known structural phase transitions in (CH3)4NCdBr3 are reported.

The title structure, [Zn(SeO(4))(CH(4)N(2)S)(3)], is isomorphous with sulfatotris(thio-urea)zinc(II). In both structures, the Zn(2+) cation is coordinated in a tetra-hedral geometry. The corresponding intra-molecular distances are quite similar except for the Se-O and S-O distances. Although the hydrogen-bonding patterns are similar, there are some differences; in the title structure all the H atoms are involved in the hydrogen-bond pattern, in contrast to the situation in sulfatotris(thio-urea)zinc(II). No reproducible anomalies were detected by differential scanning calorimetry in the range 93-463 K until decomposition started at the higher temperature.

In the title compound, [Zn(SO4)(CH4N2S)3], the Zn2+ cation is coordinated in a tetra­hedral geometry by one O atom from a sulfate anion and the S atoms from three thio­urea ligands. There are weak N—H⋯O and N—H⋯S hydrogen bonds in the structure, some of which are bifurcated. The same crystal has also been investigated at 110 K, below a reported phase transition at 120 K. No change in the space group below 120 K was observed. On the other hand, the differences between the fractional coordinates of the corresponding atoms in the determinations at 292 and 110 K are as large as about 0.007 for the non-H atoms. Differential scanning calorimetry did not detect reproducible anomalies in the inter­val 93–503 K up to the melting point.

Seven inorganic salts of 3,5-diamino-1,2,4-triazole (dat) with inorganic acids were prepared within our project focused on the crystal engineering of novel NLO materials and their X-ray structures were determined. Three triclinic compounds, dat(1+) selenate dihydrate, dat(1+) sulphate dihydrate and dat(1+) perchlorate, crystallize in the space group P. Three monoclinic structures of dat(1+) – i.e. nitrate, chloride hemihydrate and hydrogen phosphite crystallize in P21/c, P21/n and P21/c, respectively. Finally, the most promising structure of dat(1+) dihydrogen phosphate is orthorhombic (the space group Fdd2). The structure is formed by anionic layers parallel to the ac plane and the cationic chains parallel to the c axis. The FTIR and Raman spectra of the title compounds have been recorded and discussed. The assignment of the spectra is based on a quantum-chemical calculation and the factor group analysis. Quantitative powder measurements of the second harmonic generation of the only non-centrosymmetric dat(1+) dihydrogen phosphate at 1064 nm were performed and a relative efficiency equal to KDP (i.e. potassium dihydrogen phosphate) was observed. The consequent study of single crystal samples enabled the estimation of NLO tensor coefficients of this material.

Three novel inorganic salts of aniline with sulfuric and selenic acids were prepared and characterized by X-ray structural analysis. Anilinium(1+) selenate, (C6H5NH3+)2SeO42−, and anilinium sulfate, (C6H5NH3+)2SO42−, crystallize in the monoclinic space groupC2. The crystal structures are based on hydrogen bonded layers of alternating anilinium cations and inorganic anions. Anilinium(1+) selenate dihydrate, (C6H5NH3+)2SeO42−·2H2O, crystallizes in the monoclinic space groupC2/c. The crystal structure is formed by a network of alternating anilinium cations, selenate anions and water molecules connected by a system of intermolecular hydrogen bonds. The FTIR and Raman spectra of all the compounds have been recorded and discussed as well as their crystal structures. According to the DSC curves and temperature dependence of lattice parameters, anilinium sulfate exhibits phase transitions at 217 and 182 K. The appropriate changes of vibrational spectra were also recorded during cooling of the sample especially in the N–H stretching and sulfate antisymmetric stretching (ν3SO42−) spectral regions. The quantitative measurements of the second harmonic generation at 1064 nm were performed using powdered samples of anilinium sulfate, anilinium chloride and anilinium selenate, and the relative efficiencies deff = 0.05dKDP, deff = 2.33dKDP and deff = 0.05dKDP (KDP; i.e.KH2PO4) have been observed, respectively.

Tris-sarcosine calcium chloride (TSCC) single crystals were grown from water solutions by the isothermal evaporation method. The growth solutions contained sarcosine and CaCl2 either in stoichiometric or nonstoichiometric ratio. The required phase diagram sarcosine–CaCl2H2O at 40 °C was determined by the synthetic method. PFT 400 MHz NMR was used for the analysis of organic impurities in sarcosine and TSCC. The crystals grown from both types of solutions had maximum values of the dielectric permittivity 10 to 200 times larger than those measured by other authors at comparable measuring frequencies and fields. It is discussed in terms of crystal quality. Trisarcosin-Calciumchlorid (TSCC) Einkristalle wurden nach der Methode der isothermen Verdampfung aus wasrigen Losungen gezuchtet. Die Zuchtungslosungen enthielten Sarcosin und CaCl2 in stochiometrischer oder nichtstochiometrischer Zusammensetzung. Das Phasendiagramm Sarcosin–CaCl2H2O wurde bei 40 °C nach der synthetischen Methode bestimmt. Puls-Fourier-Transform NMR bei 400 MHz wurde zur Analyse organischer Verunreinigungen in Sarcosin und TSCC benutzt. Die Kristalle aus beiden Arten von Losungen hatten Maximalwerte der Dielektrizitatskonstanten, die um den Faktor 10 bis 200 groser waren, als sie von anderen Autoren bei vergleichbaren Mesfrequenzen und Feldern gemessen wurden. Dies wird im Zusammenhang mit der Kristallqualitat diskutiert.

Raman and infra-red spectroscopic investigations of nominally pure SrTiO 3 ceramics have revealed a clear presence of polar phase whose manifestation steeply increases on cooling from room temperature. The Raman strengths of the Raman-forbidden infra-red modes are proportional to ω TO1 − α ( α ≈ 1.5) where ω TO1 is the polar soft mode frequency. Our explanation is based on an assumption of a temperature independent polarization P f fixed at grain boundaries. The effective polar soft mode is slightly shifted upwards at low temperatures, becomes broader and strongly coupled with the E g component of the structural soft mode which shows that P f is perpendicular to the tetragonal c -axis.

Eight inorganic salts of 2-amino-1,3,4-thiadiazole (2-athd) with hydrochloric, perchloric, nitric, sulphuric, selenic, phosphorous and phosphoric acids were prepared, and their crystal structures were determined. Seven of the compounds crystallise in monoclinic space groups – i.e., 2-athd(1+) chloride monohydrate (P21/c), 2-athd(1+) selenate monohydrate (Pc), 2-athd(1+) dihydrogen phosphate (Cc), 2-athd(1+) phosphite (P21/a), 2-athd(1+) nitrate (P21/c), 2-athd(1+) 2-athd perchlorate (P21/n) and 2-athd(1+) perchlorate (P21/c) – and one crystallises in an orthorhombic space group – 2-athd(1+) hydrogen sulphate (P212121). The thermal behaviours of the materials were studied (DSC) down to liquid nitrogen temperature, and the properties of the perchlorate, hydrogen sulphate and selenate monohydrate crystals were discussed with respect to the results of high or low-temperature X-ray diffraction, IR and Raman spectroscopic studies. Quantitative measurements of the second harmonic generation of the powdered non-centrosymmetric samples at 1064 and 800 nm were performed and a relative efficiency compared to KDP is presented.