M. Maczka

Polish Academy of Sciences | PAN

Hybrid organic–inorganic halides have traditionally been viewed as materials that adopt well-ordered structural phases at low temperatures. In this article, we report a one-dimensional perovskitoid aminoguanidinium lead iodide (AGAPbI3) with a first-order phase transition at 400/369 K (during heating/cooling) that breaks away from this rule. Specif...

Compared to their three-dimensional analogues, the layered perovskites A2BX4 (A= organic cation; X = Br, I, Cl) display higher anisotropy, elasticity and sensitivity to external stimuli. In this study, we employ a combination of diffraction, calorimetric, dielectric, vibrational and optical measurements to uncover rich phase diversity and atypical...

This study revisits a (001)-oriented layered lead chloride templated by 1,2,4-triazolium, Tz2PbCl4, which recently has been an object of intense research but still suffers from gaps in characterization. Indeed, the divergent reports on the crystal structures of Tz2PbCl4 at various temperatures, devoid of independent verification of chiral phases th...

Lattice symmetrization is a term coined for the intentional doping of methylammonium lead iodide (MAPbI3) with larger organic cations to lower the transition temperature to the cubic phase, whose stability is much preferred over the tetragonal one to avoid undesired lattice strain harmful for device operation, which could appear due to the cubic-te...

By using Raman spectroscopy, we demonstrate that [IM]Mn(H2POO)3 is a highly compressible material that undergoes three pressure-induced phase transitions. Using a diamond anvil cell we performed high-pressure experiments up to 7.1 GPa, using paraffin oil as the compression medium. The first phase transition, which occurs near 2.9 GPa, leads to very...

Two-dimensional (2D) lead halide perovskites are a family of materials at the heart of solar cell, light-emitting diode, and photodetector technologies. This perspective leads to a number of synthetic efforts toward materials of this class, including those with prescribed polar architectures. The methylhydrazinium (MHy+) cation was recently presume...

Hybrid organic-inorganic lead halide perovskites have emerged as promising materials for various applications, including solar cells, light-emitting devices, dielectrics, and optical switches. In this work, we report the synthesis, crystal structures, and linear and nonlinear optical as well as dielectric properties of three imidazolium lead bromid...

Mixing of molecular cations in hybrid lead halide perovskites is a highly effective approach to enhance stability and performance of the optoelectronic devices based on these compounds. In this work, we prepare and study novel mixed methylammonium (MA)-ethylammonium (EA) MA1-xEAxPbI3 (x < 0.4) hybrid perovskites. We use a suite of different techniq...

The application of high pressure allows tuning physicochemical properties of materials by changing interatomic distances. Pressure may also induce structural phase transitions into new phases with enhanced or novel functional properties. Here, we report complementary high-pressure single-crystal X-ray diffraction, Raman spectroscopy, and optical st...

One-dimensional hybrid organic-inorganic halide perovskites have recently come under the spotlight of research due to their unique optical properties, including strong light absorption and other physicochemical characteristics relevant for energy conversion applications. Exchanging organic cations in the perovskite lattice is known to strongly affe...

Hybrid organic-inorganic perovskites comprising hypophosphite ligands are emerging functional materials exhibiting magnetic, photoluminescence, negative thermal expansion and negative linear compressibility behaviours. This work reports five novel hypophosphite perovskites, [A]M(H2POO)3 (A = pyrrolidinium (PYR+), guanidinium (GUA+) and imidazolium...

Applications of two-dimensional (2D) perovskites have significantly outpaced the understanding of many fundamental aspects of their photophysics. The optical response of 2D lead halide perovskites is dominated by strongly bound excitonic states. However, a comprehensive experimental verification of the exciton fine structure splitting and associate...

A proper understanding of structural phase transitions and cation dynamics in hybrid lead halide perovskites is important for further enhancement of the photovoltaic properties of these materials. Here, we propose a model describing the FA cation ordering in FAPbX3 (X = Br, I) hybrid perovskites. Our model is based on the available structural infor...

Three-dimensional hybrid organic–inorganic lead halide perovskites are promising photovoltaic and light-emitting materials. A key phenomenon relevant for their optoelectronic applications is electron–phonon coupling. Since it can be strongly modified by structural deformation and changes in the dynamics of molecular cations, it is of great importan...

Three-dimensional hybrid organic−inorganic perovskites with halide, formate, or hypophosphite ligands are promising photovoltaic, light-emitting, and multiferroic materials. Since the properties of these compounds are strongly affected by changes in lattice dynamics, it is of great importance to understand their phonon properties. We report Raman a...

Given the need to process anodes and composites based on nano-YSZ in reducing atmosphere or in air containing carbon atmospheres for the fabrication of solid oxide fuel cells (SOFCs) and solid oxide electrolysis cells (SOECs), we have studied the effect of the exposure to CO+N2/H2 or CO2+air mixtures during sintering of YSZ green pellets, prepared...

Three-dimensional lead halide perovskites are promising materials for optoelectronic applications. The most famous representative comprise methylammonium (MA⁺) and formamidinium (FA⁺) cations, but recently, this group was enlarged by methylhydrazinium (MHy⁺) analogues that crystallize in polar structures at room-temperature. Properties of three-dim...

Metal formates are a subclass of cordination polymers that is renowned for rich phase transition behaviour arising from complex interplay of molecular dynamics of organic guests and surrounding coordination net....

Hybrid organic–inorganic perovskites providing integrated functionalities for multimodal switching applications are widely sought-after materials for optoelectronics. Here, we embark on a study of a novel pyrrolidinium-based cyanide perovskite of formula (C4H10N)2KCr(CN)6, which displays thermally driven bimodal switching characteristics associated...

Hypophosphite hybrid perovskites have recently received widespread attention due to their diverse structural and magnetic properties, negative thermal expansion and photoluminescence behaviour. Herein, we report two new three-dimensional hybrid perovskites containing unusually large organic cations, pyrrolidinium and 2-hydroxyethylammonium. We repo...

Hybrid organic–inorganic perovskites (HOIPs) constitute unique coordination polymers with a huge potential of transforming modern materials chemistry due to their wide applications, mainly in electronics, optoelectronics and photovoltaics. Yearly, thousands of works on HOIPs are published in various fields of science, technology and industry. Many...

A combination of structural, dielectric and calorimetric studies is used to describe a highly atypical behaviour of novel hybrid formate [NH3(CH2)3NH2(CH2)3NH3][Mn(HCOO)3]3, incorporating large triprotonated molecular cation. Two successive phase transitions, switching between fast multiple rotor modes, and surprising probable coexistence of static...

In this work the crystal structure of the new hybrid organic-inorganic compound has been studied using single-crystal X-ray diffraction (SCXRD). Methylhydrazinium lead iodide (MHyPbI3) crystallizes in monoclinic, centrosymmetric P21/c space group with a=4.5067(4) Å, b=19.1892(16) Å, c=12.0029(12) Å and β=98.178(8). The structure is built of edge-sh...

Coordination polymers with multiple non-centrosymmetric phases have sparked substantial research efforts in the materials community. We report the synthesis and properties of a hitherto unknown cadmium dicyanamide coordination polymer comprising benzyltrimethylammonium cations (BeTriMe+). The room-temperature (RT) crystal structure of [BeTriMe][Cd(...

p>We use a multi-technique approach to determine the phase diagram and molecular cation dynamics of mixed methylammonium-formamidinium MA1-xFAxPbBr3 (0 ≤ x ≤ 1) hybrid perovskites. The calorimetric, ultrasonic and X-ray diffraction experiments show a substantial suppression of the structural phase transitions and stabilization of the cubic phase up...

A series of pressure-induced phase transitions between [MHy]Mn(H2POO)3 (MHy⁺ = methylhydrazinium) phases reveals the structural mechanism behind the elastic properties of this hypophosphite perovskite. In the ambient pressure phase α, NH···O hydrogen bonds to H2POO– linkers stabilize the MHy⁺ cations outside the perovskite cages. When pressure incr...

An expansive library of structurally complex two-dimensional (2D) and three-dimensional (3D) lead halide perovskites has emerged over the past decade, finding applications in various aspects of photon management: photovoltaics, photodetection, light emission, and nonlinear optics. Needless to say, the highest degree of structural plasticity enjoys...

In this work, we compare the dielectric properties of single-crystal and pelletized perovskite-like formamidinium-templated inorganic-organic hybrid [NH2CHNH2][Mn(HCOO)3] (FAMn) at ambient pressure. Furthermore, we report pressure-dependent dielectric measurements of pelletized FAMn allowing us to determine the equation of state, as well as changes...

Fast ON/OFF switches are the basis of contemporary microelectronics. Dielectrics alternating between high and low dielectric permittivity states (ON and OFF, respectively) seem to be up-and-coming candidates for efficient switches. Currently, the change of their state is induced by a temperature gradient, which is a relatively slow process. In this...

The recently discovered hypophosphite perovskites are promising functional materials. This contribution is devoted to the structural, thermal, dielectric, Raman and optical studies of a new hybrid organic-inorganic perovskite, [FA]Cd(H2POO)3 (FA= formamidinium, NH2CHNH2+). We also report the thermal, magnetic, dielectric and optical properties of t...

We report density functional theory (DFT) studies of vibrational modes for benzyltrimethylammonium cations (BeTriMe⁺) as well as THz, IR and Raman studies of [BeTriMe][M(dca)3(H2O)] (dca=N(CN)2⁻, dicyanamide; M=Mn²⁺, Co²⁺, Ni²⁺) and their anhydrous analogues. These studies show that the anhydrous BeTriMeMn and BeTriMeNi have the same or very simila...

Highly stable ferroelectrics with reversible high-temperature phase transitions and switchable nonlinear optical behaviour are much coveted targets for emerging optoelectronic applications. Here, we demonstrate a cyano-bridged perovskite [(CH3)3NOH]2[KCo(CN)6] (TMAO-Co), a new analogue of the multi-axial ferroelectric [(CH3)3NOH]2[KFe(CN)6] (TMAO-F...

Three-dimensional methylhydrazinium (CH3NH2NH2⁺, MHy⁺) lead halides, related to the famous methylammonium (CH3NH3⁺, MA⁺) and formamidinium (CH(NH2)2⁺, FA) perovskites, are attractive optoelectronic materials crystallizing in polar structures. In this work, temperature-dependent ¹H and ²⁰⁷Pb magic-angle spinning (MAS) NMR, Raman as well as high-pres...

Recently discovered hybrid perovskites based on hypophosphite ligands are a promising class of compounds exhibiting unusual structural properties and providing opportunities for construction of novel functional materials. Here, we report for the first time the detailed studies of phonon properties of manganese hypophosphite templated with methylhyd...

The rich dielectric properties of hybrid formate frameworks are tightly related to the dipolar dynamics and phase transitions of these compounds. A complete understanding of such phenomena requires experiments performed under non-standard conditions. Herein, we report high-pressure dielectric properties of anisotropic single crystal of 1,4-diaminob...

Cation engineering provides a route to control the structure and properties of hybrid halide perovskites, which has resulted in the highest performance solar cells based on mixtures of Cs, methylammonium, and formamidinium. Here, we present a multi-technique experimental and theoretical study of structural phase transitions, structural phases and d...

Metal-formate frameworks comprising ammonium cations as guests proven to be fertile ground to study various phenomena associated with the temperature-induced changes in structural, dielectric, optical and magnetic properties. In this contribution, we revisit NH4[Cu(HCOO)3], a member of metal-formate that distinguishes itself in terms of its phase t...

We report the synthesis, crystal structures, thermal, optical and magnetic properties of three new metal dicyanamide frameworks comprising benzyltrimethylammonium cations (BeTriMe+) as labile guests. These compounds crystallize in as two-dimensional noncentrosymmetric structures, in space group Pna21 of the orthorhombic system, in which metal catio...

Two three-dimensional metal-organic compounds of the formula Pyr2KM(CN)6, where M = Co, Fe and Pyr = pyrrolidinium ((CH2)4NH2+), have been found to crystallize at room temperature in a monoclinic structure, space group P21/c. They are cyano-bridged compounds with an unprecedented type of architecture containing pyrrolidinium cations in the voids. T...

Hybrid perovskites based on hypophosphite ligands constitute an emerging family of compounds exhibiting unusual structures and offering a platform for construction of novel functional materials. We report the synthesis, crystal structure, and magnetic and optical properties of novel undoped and HCOO⁻-doped manganese hypophosphite frameworks templat...

Methyl groups are ubiquitous in synthetic materials and biomolecules. At sufficiently low temperature, they behave as quantum rotors and populate only the rotational ground state. In a symmetric potential, the three localized substates are degenerate and become mixed by the tunnel overlap to delocalized states separated by the tunnel splitting ν t...

We present an X- and Q-band continuous wave (CW) and pulse electron paramagnetic resonance (EPR) study of a manganese doped [NH4][Zn(HCOO)3] hybrid framework, which exhibits a ferroelectric structural phase transition at 190 K. The CW EPR spectra obtained at different temperatures exhibit clear changes at the phase transition temperature. This sugg...

Formation of noncentrosymmetric three-dimensional (3D) lead halide perovskites has been a widely sought after goal since polar structure opens up new vistas to properties of these materials, e.g. improved charge separation for photovoltaics arising from ferroelectric order. Here, we report growth and unique properties of a new highly distorted 3D p...

We present X- and Q-band continuous wave (CW) and pulse electron paramagnetic resonance (EPR) study of manganese doped [NH4][Zn(HCOO)3] hybrid framework, which exhibits a ferroelectric structural phase transition at 190 K. The CW EPR spectra obtained at different temperature exhibit clear changes at the phase transition temperature. This suggests a...

Sodium potassium copper(II) tetra-[molybdate(VI)], Na0.45K1.55Cu3(MoO4)4, was synthesized using solid-state reaction route, and its crystal structure (monoclinic P21/c) was solved using single-crystal X-ray diffraction method. Na0.45K1.55Cu3(MoO4)4 forms 3D framework with elongated cavities occupied by alkali ions. The factor group analysis of Na0....

Three-dimensional (3D) lead halide perovskites have emerged as a promising class of coordination polymers for solar cells, photodetectors and light emitting devices. These compounds thus far comprised methylammonium, formamidinium or cesium as cations. In this work, we introduce a new methylhydrazinium 3D perovskite, CH3NH2NH2PbBr3 that crystallize...

The detailed temperature-dependent IR and Raman spectra were used to study and understand the mechanism of structural phase transition occurring at 175 K in manganese hypophosphite templated with formamidinium (FA+) ions, [FA]Mn(H2POO)3, which adopts a perovskite-like architecture. The structural transformation between the C2/c and the P21/c monocl...

This contribution is devoted to the linear and nonlinear optical studies of two three-dimensional (3D) perovskite-like metal-organic frameworks, [(C3H7)4N][Cd(N(CN)2)3] and [(C3H7)4N][Mn(N(CN)2)3]. Band gap energy (5.02 eV) of Cd-analogue is slightly smaller than that for its manganese counterpart (5.17 eV); values of energy gaps are determined fro...

A non-centrosymmetric, polar LiNa5Mo9O30 single crystal was grown using Kyropoulos technique and characterized by polarized Raman scattering and polarized infrared specular reflection spectroscopy at room temperature. The comparison to the polycrystalline spectra has been made and assignment of all observed modes to the respective vibrations and th...

Layered lead halides offer potential for light emitting and photovoltaic devices. Here, we report synthesis of two-dimensional (2D) lead iodide with single-octahedra slabs separated by the smallest organic cation used up to now in the construction of A2PbI4 compounds. This compound, MHy2PbI4, where MHy+ denotes methylhydrazinium cation, shows excep...

Dimethylammonium zinc formate[(CH3)2NH2][Zn(HCOO)3] (DMAZn) treated as a model dense metal-organic framework is a compound being intensively studied in the last decade. It undergoes a first order order-disorder structural phase transition at T0~166 K, considered as the improper ferroelectric one. The complex mechanism of this phase transition is at...

We report the synthesis, crystal structures, thermal, optical and phonon properties of four new metal dicyanamide frameworks templated using tributylmethylammonium cations (TriBuMe+). Our results show that these compounds crystallize in a three-dimensional perovskite-like monoclinic structure, space group P21/n, with two inequivalent TriBuMe+, one...

We present a theoretical model of the methylhydrazinium CH3NH2NH2⁺ molecular cation ordering in perovskite [CH3NH2NH2][M(HCOO)3] (M = Mn, Mg, Fe and Zn) formate frameworks, which exhibit two structural phase transitions. The proposed model is constructed by analyzing the available structural information and mapping the molecular cation states on a...

The single crystals of Na2Mn2(MoO4)3 were successfully grown using the solid-state synthesis method. This compound crystallizes in a triclinic system with space group P1‾ (Ci). Its structure can be described as a three-dimensional anionic framework of Mn2O10 double octahedra units sharing edges with the MoO4 tetrahedra. The Na⁺ ions are disordered...

We report complementary high-pressure Raman and single-crystal X-ray diffraction studies of a perovskite-like dicyanamide framework of [(C3H7)4N][Mn(N(CN)2)3] ([TPrA][Mn(dca)3]). Our studies show that the bulk modulus of the ambient pressure P21c phase is B0 = 8.1(11) GPa, and the ab-plane compresses by 54.4(15) × 10⁻³ GPa⁻¹ and the c-axis by 8.0(1...

We report the high-pressure structure-related properties of a ferroelectric heterometallic formate perovskite framework templated by the ethylammonium cation (CH3CH2NH3⁺, EtA⁺). The high-pressure X-ray diffraction studies show a first-order structural phase transition at 3.6(2) GPa from the polar Pn ambient phase to a centrosymmetric P21/n high-pre...

We report the synthesis and dielectric characterization of novel polyvinylidene fluoride-trifluoroethylene P(VDF-TrFE) composite films containing [(CH3)2NH2][Mg(HCOO)3] (DMAMg) and [NH4][Zn(HCOO)3] (AmZn) dense metal-organic frameworks (MOFs). The optical camera and Raman microscopies are used to map the distribution of the MOF fillers in the prepa...

The indications of peculiar multiferroic behavior of dimethylammonium metal-formate perovskite frameworks raised important questions about the origin of the structural phase transition, structural phases and dipolar dynamics in these compounds. Here we provide answers on some of these phenomena by presenting a comprehensive experimental and theoret...

We present a combined study of [(CH3)2NH2][Cd(N3)3] hybrid perovskite dense metal-organic framework by IR, Raman, continuous-wave electron paramagnetic resonance (CW EPR), phase-transition-induced current and dielectric measurements. The Raman and IR study has shown that the phase transition observed near 175 K is associated with a pronounced narro...

We report temperature-dependent X-ray diffraction, thermal, dielectric, electron paramagnetic resonance (EPR), Raman and IR studies of [(C3H7)4N][Cd(N(CN)2)3] ([TPrA][Cd(dca)3]) exhibiting a rich sequence of temperature-induced phase transitions occurring at T3 = 386 K, T2 = 362 K, T1 = 241 K and T0 = 228 K. The X-ray diffraction study confirms the...

We report the synthesis, crystal structure, and thermal, dielectric, optical and phonon properties of a new two-dimensional (2D) cadmium(II) complex [(C3H7)4N][Cd(N(CN)2)3]. Our results show that this compound crystallizes in a two-dimensional monoclinic structure, with the space group P2/n, with ordered tetrapropylammonium cations and disorder of...

Polycrystalline sample of the sodium aluminum molybdate, NaAl(MoO4)2, was prepared by conventional solid-state reaction method. Ultraviolet-visible-near-infrared (UV-Vis-NIR) diffuse reflectance spectroscopy revealed that the optical band gap values of this material at ambient conditions are 3.77 and 3.35 eV for direct and indirect transition, resp...

This work describes the synthesis, structural characterization and electrical properties of solid solutions with the general formula Gd2Hf2−xBx O7, where B = Ti⁴⁺, Sn⁴⁺ and Zr⁴⁺. All samples were successfully prepared in ~ 30 h, via a mechanochemical reaction in a planetary ball mill, using the corresponding elemental oxides as starting chemicals....

We report the synthesis, thermal and dielectric measurements of [NH2NH3][Mn(HCOO)3] (HyMn) compound. Above room temperature this polymeric material undergoes two phase transitions at ∼360 K and ∼298 K, as observed via DSC and BDS spectra. The first high temperature phase transition is associated with the paraelectric to ferroelectric transition of...

Depending on intrinsic (e.g., radius ratio rule rLn/ rZr) and extrinsic factors (e.g., processing conditions), pyrochlore-type Ln2Zr2O7 oxides achieve variable degrees of structural disorder. We report on a systematic study of the structural and microstructural characteristics of the Gd2- xLn xZr2O7 system, exploring the effect of replacing Gd with...

Lithium tantalate is a well-known optical crystal. The dispersion relation of phonon-polaritons was studied in ferroelectric lithium tantalate crystals. The reflectivity spectra of E//x and E//z polarizations, which are related to E(x,y) and A1(z) symmetry modes respectively, were measured by the FT-IR measurement in the far- and mid-IR regions. Th...

Isodimorphism for two Aurivillius phases BaBi4Ti4O15 and CaBi4Ti4O15 with different symmetry was studied. Synthesis techniques have been optimized and solid solution with the composition Ba1-xCaxBi4Ti4O15 (х – molar part of the component, x = 0, 0.25, 0.5, 0.75, 1) have been prepared. The structure of the compounds has been studied using X-ray diff...

Dimethyl ammonium (DMA) metal formate, an important member of the dense metal organic framework (MOF) family, is known to exhibit a low temperature ferroelectric transition, caused by the ordering of the hydrogen bonds. In this study we have probed the effect of pressure on the disordered hydrogen bond and the HCOO⁻ linkers of DMA manganese formate...

Metal–organic frameworks (MOFs), in which framework is formed of metal centers coupled by organic molecules, exhibit inherent porosity and crystallinity. Although these systems have been examined for vast potential applications, the multiferroic properties in MOFs still remain poorly understood. One of the approaches to get insight into the ferroic...

Monotonic compression of two iso-structural hybrid metal-organic perovskites [DMA]M(HCOO)3 (M = Co, Ni) has been connected to the structural distortions. The strongest effects of pressure occur in the tilts of the MO6 octahedra, MO bonds compression, angular distortions within the MO6 octahedra and small folding between the octahedra and formate un...

We present a combined differential scanning calorimetry (DSC), infrared (IR), Raman, electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR) study of dimethylammonium zinc formate frameworks [(CH3)2NH2][Zn(HCOO)3] containing ¹⁴N and ¹⁵N nitrogen isotopes. The DSC reveals very small differences in the phase transition temperatures...

We report a continuous-wave (CW) and pulse electron paramagnetic resonance (EPR) as well as pulse electron nuclear double resonance (ENDOR) study of Cu²⁺ doped [(CH3)2NH2][Zn(HCOO)3] hybrid perovskite which exhibits a structural phase transition. The multifrequency (X, Q and W-band) CW EPR measurements allow to study the temperature evolution of th...

Eu3+ complex with 1-(2,6-dihydroxyphenyl)ethanone in the solid state has been synthesized and characterized by elemental analysis, UV-visible, FT-IR and FT-Raman spectroscopies, powder X-ray diffraction, electron emission under femtosecond laser excitation. The stoichiometry and the formula of the studied complex have been proposed. Its physicochem...

A solid state Eu³⁺ complex with dehydroacetic acid (DHA) has been synthesized and characterized by elemental analysis, UV–visible, FT-IR, FT-Raman, powder and single-crystal X-ray diffraction and optical spectroscopy studies. The complex has formula [Eu(DHA)2(H2O)5]NO3 with DHA = C8H7O4⁻, where the europium ions is in monocapped distorted square an...

The dispersion relation of Raman inactive phonon-polaritons with T1u symmetry was studied in quantum paraelectric SrTiO3 with centrosymmetric Pm3¯m in which no Raman active mode is allowed. The reflectivity in the far- and mid-IR regions was measured using a [001] crystal plate by the reflection FT-IR spectroscopy, and the complex refractive index...

We report synthesis of two novel mixed-valence iron(II)-iron(III) formate frameworks templated by N-ethylmethylammonium (EtMeA⁺) and 2-Hydroxyethylammonium (HEA⁺) cations. X-ray diffraction shows that these compounds crystallize in the P 3¯1c niccolite-type structures. Optical studies confirm mixed-valence character of these compounds. Magnetic inv...

Four novel compounds, [NH3CH2CH2OH][MIIIMII(HCOO)6] with MIII = Fe and MII = Mn (HEAFeMn), MIII = Fe and MII = Ni (HEAFeNi), MIII = Cr and MII = Mn (HEACrMn) and MIII = Cr and MII = Co (HEACrCo), have been synthesized. They crystallize in the trigonal niccolite-type structure (space group P 3¯ 1c). Magnetic studies revealed that HEAFeNi, HEAFeMn an...

We report high-pressure Raman scattering studies of acetamidninium manganese formate, which show evidence for two pressure-induced phase transitions between 0.7 and 1.4 GPa and above 5.3 GPa. The first transition is related to distortion of the manganese formate framework whereas the second one affects significantly the structure of the acetamidini...

We present a pulse electron paramagnetic resonance (EPR) and electron-nuclear double resonance (ENDOR) study of a manganese doped [(CH3)2NH2][Zn(HCOO)3] dense metal-organic framework which exhibits a structural phase transition at 163 K. The echo-detected field sweep Mn²⁺ EPR spectrum of the low-temperature phase is in a perfect agreement with the...

This work describes the mechanochemical synthesis, structural characterization and electrical properties of an interesting group of novel ionic conductors, with general formula Gd2(Hf2−xTix)2O7. Different compositions in this system (x = 0, 0.4, 0.8, 1.2, 1.6 and 2) were obtained at room temperature, via a mechanochemical reaction between the corre...

The compounds Bi2MoO6 (m = 1), Bi2WO6 (m = 1), Bi3NbTiO9 (m = 2), Bi4Ti3O12 (m = 3) and CaBi4Ti4O15 (m = 4) (Aurivillius phases with the general formula Аm–1Bi2BmO3m+3) have been synthesized by solid state reaction method. Using the high-temperature X-ray diffraction, the phase transition and melting temperatures have been determined for these comp...

The complex impedance of β-Na4Cu(MoO4)3 was investigated in the 573–833 K temperature range and 40 Hz–5 MHz frequency range. The Nyquist plots have been successfully analysed by an equivalent of series combination of grains and grain boundaries elements. This analysis revealed presence of two relaxation phenomena and revealed that grain boundaries...

We report synthesis of four novel heterometallic MOFs, [(NH4)(H2O)][CrIIIMII(HCOO)6] with MII = Zn (NH4CrZn), Co (NH4CrCo), Mn (NH4CrMn) and Ni (NH4CrNi). X-ray diffraction shows that NH4CrZn crystallizes in the trigonal structure (space group P3¯1c) with ordered Cr³⁺ and Zn²⁺ centers while NH4CrCo, NH4CrMn and NH4CrNi crystallize in the hexagonal...

The high power conversion efficiency of the hybrid CH3NH3PbX3 (where X = I, Br, Cl) solar cells is believed to be tightly related to the dynamics and arrangement of the methylammonium cations. In this Letter, we propose a statistical phase transition model which accurately describes the ordering of the CH3NH3⁺ cations and the whole phase transition...

We present a continuous wave electron paramagnetic resonance (EPR) study of Mn²⁺ doped [(CH3)2NH2][Zn(HCOO)3] hybrid dense metal-organic framework (MOF) that exhibits an order-disorder structural phase transition at Tc = 163 K. The W-band EPR measurements of powder sample are performed to verify the previously reported spin Hamiltonian parameters o...

The complex impedance of Na 2 K 2 Cu(MoO 4 ) 3 material has been investigated in the temperature range of 653–753 K and in the frequency range of 40 Hz–5 MHz. Electrical behavior of the studied material is explained through an equivalent circuit model which takes into account the contributions of grains and grains boundaries. The number of vibratio...

A set of five novel formate frameworks templated with the assemblies comprising diprotonated 1,2-diaminoethane (DAE) and water molecule of the formula: [NH3(CH2)2NH3]M2(HCOO)6•H2O, where M = Mg, Mn, Co, Ni, Zn, has been synthesized. Four compounds crystallize in polar R3 and one - in chiral P6322 space group (Ni-analogue) at room temperature. The p...

We report the synthesis, crystal structure, thermal , dielectric, phonon and magnetic properties of [CH3C(NH2)2][Mn(HCOO)3] (AceMn) compound. Our results show that this compound crystallizes in the perovskite-like orthorhombic structure, space group Imma. It undergoes a structural phase transition at 304 K into a monoclinic structure, space group...

Eu³⁺ complex with 2-hydroxy-4-metoxy-benzophenone (HMBP) in solid state has been synthesized and characterized by elemental analysis, UV-visible, FT-IR, FT-Raman spectroscopies, powder X-ray diffraction, electron emission excited by femtosecond pulses. The stoichiometry and formula of the studied complex have been proposed. Its physicochemical prop...