Crystallographic Phase Transition Research Articles

Structural origins of dielectric anomalies in the filled tetragonal tungsten bronze Sr2NaNb5O15

The tetragonal tungsten bronze, Sr2NaNb5O15, shows promise for application in high-temperature high-efficiency capacitors vital for the sustainable energy revolution. Previously, the structural complexity of this and related materials has obscured the mechanisms underpinning two large anomalies in relative permittivity (εr) which give rise to their exceptionally broad dielectric response. Here, we comprehensively investigate the structural evolution from −173 to 627 °C, combining electron, X-ray and neutron diffraction, electron microscopy, and first principles electronic structure calculations to unambiguously identify the structural origins of both anomalies. The peak in εr at 305 °C is associated with a polar-nonpolar phase transition, wherein cations displace along the c axis. Guided by DFT, we identify a further transition upon cooling, associated with the second peak at −14 °C, linked to the softening of an in-plane polar distortion with a correlation length limited by ferroelastic nano-domains arising from rigid-unit-like tilting of NbO6 octahedra at high temperature, imparting relaxor-like behaviour. Thus, the two dielectric anomalies in Sr2NaNb5O15 are associated with two distinct crystallographic phase transitions and their interplay with a microstructure that arises from a third, non-polar structural distortion. Chemical control of these will enable development of tuneable materials with dielectric properties suitable for high-temperature energy storage applications.

Dynamic shock wave processing on β-MnMoO4 ceramic micro-sized crystals and its structure-morphology-property relations

In the present work, we perform a few shock-wave-processing experiments on typical ceramic materials of β-MnMoO4 (P2/c) by the exposure of 0, 100 and 200 shocks, respectively, and investigated their structural, optical and morphological features to materialize the effect of shock waves. Under shocked conditions, the title sample does not undergo any crystallographic phase transitions of either to α or to ω phases. However, several modifications are noticed in the mother phase such that the diffraction intensity ratio of (1-11)/(111) is found to have increased with respect to the number of shock pulses and the observed values are 0.85, 1.07 and 1.36 for the exposure of 0, 100, 200 shocks, respectively. Under the 200-shocked condition, the sample's intensity ratio is found to be closely matched to the standard pattern of the test sample with the P2/c space group. In morphological aspects, the control sample's wolframite structure has slight morphological deformations whereas the 200-shocked sample has an almost ideal morphology of the wolframite structure. Optical property results demonstrate a slight enhancement of the optical transmittance in the UV–Visible and NIR regions along with a blue shift at the 200-shocked condition. The above-mentioned analytical results reveal that the applied shock waves have effectively induced the thermal softening process, reducing the lattice and surface stresses on the test sample. A detailed discussion on the triangle relation of the structure-morphology-property of the control and shocked samples is provided.

Intertwined crystal structure, magnetic, and charge transport properties in mixed valent A-site ordered manganite NdBaMn2O6

In the present work, we report a correlation between crystal structure, magnetic, and electrical properties in an exotic magnetic compound, NdBaMn2O6 having ∼92% ordering between Nd and Ba, investigated using temperature-dependent synchrotron x-ray diffraction (XRD), dc magnetization and transport measurements. Temperature-dependent XRD data reveals that the compound undergoes various complex crystallographic phase transitions from high-temperature (T > 320 K) P4/mmm phase to intermediate (320 K – 280 K) Cmmm phase to a mixed (Cmmm and P21am) phase (280 K – 220 K) and to low-temperature P21am phase (T < 220 K). It is found that these crystallographic phase compositions play a crucial role in controlling its magnetic and transport properties. Temperature-dependent dc magnetization data show a sharp drop at the onset of mixed phase (Cmmm + P21am) at 280 K followed by a broad hump at ∼ 220 K where mixed phase to P21am transition occurs, thus indicating a correlation between the structural and magnetic properties. The dc magnetization in the mixed phase region is calculated by considering a superposition of the magnetic moments of Cmmm and P21am phases weighted by the fraction of each phase, which exactly follows the experimental magnetization data. Temperature variation of resistivity data shows a jump at ∼260 K, a temperature corresponding to 50–50% phase composition of Cmmm and P21am phases. The compound shows insulating behavior over a whole temperature range as confirmed from the resistivity data. Further, application of magnetic field causes a shift of magnetic and transport transition temperatures which may be due to the magnetic field induced structural transition in the system.

Experimental evidence on the sustainability of crystallographic and chiral symmetry of L-alanine under dynamic shocked conditions

Over the years, crystallographic phase transitions of the polar and non-polar amino acids under static high-pressure-temperature conditions have been well documented, especially after the development of the diamond anvil cell techniques. In contrast, the crystallographic structural science of such primary amino acids under dynamic shocked conditions is still to be explored substantially as it is in a premature stage which requires being loaded with a few possible deep insights whereby exploring the structural kinetics could be a reality. In the present context, we have performed the acoustic shock wave recovery experiment on non-polar amino acid of L-Alanine powder samples such that X-ray diffraction (XRD) and circular dichroism (CD) spectroscopic techniques have been enabled to investigate the structural and chiral stability under shocked conditions. Based on the observed results, it is observed that the crystallographic structure with the P212121 space group and the same chirality is maintained even at the 200-shocked condition with a transient pressure of 2.0 MPa. The observed dynamic shock wave loading structural stability outcome is identified to be well-matched with the previous static high-pressure compression results.

Impact Of Shock Waves on Structural and Optical Properties of Li2so4.H2o Doped L-Alanine Single Crystals for High Pressure and Temperature Applications

The current study discusses the impact of shock wave of Mach number 1.7 on structural, molecular and optical properties of Li2SO4.H2O doped L-Alanine single crystals. PXRD, Raman spectral results confirm that the test crystal does not undergo any crystallographic phase transitions and conformational transitions against the shock wave. Optical micrographs and UV-Visible analysis communicate the subtle morphological changes and optical properties which is not significantly changed by shock wave. The results of crystallographic studies provide the strong proof that the crystal has molecular stability and a stable crystallographic structure against the impact of applied shock waves and suitable for a wide range of uses in aerospace applications.

Effect of Melt-Spinning Parameters on the Structure and Properties of Ni55.5Mn18.8Ga24Si1.7 Heusler Alloy Ribbons.

Ni-Mn-based Heusler alloys are known to demonstrate magnetic shape memory and giant magnetocaloric effect (MCE). These effects depend on the phases, crystallographic and magnetic phase transitions, and the crystallographic texture characteristics. These structural characteristics, in turn, are a function of the processing parameters. In the current work, Ni55.5Mn18.8Ga24Si1.7 Heusler alloy was processed by melt-spinning under a helium atmosphere. This process results in a fine microstructure. The ribbon that was produced with a narrower nozzle width, faster wheel speed, and higher cast temperature, indicating a faster cooling rate, had double the magnetic entropy change close to room temperature. However, the other ribbon demonstrated a large entropy change over a broader temperature range, extending its usability. The effect of the melt-spinning process parameters on the developing microstructure, crystallographic structure and texture, transformation temperatures, and the magnetic entropy change were studied to explain the difference in magnetocaloric behavior.

Hysteretic Spin Crossover with High Transition Temperatures in Two Cobalt(II) Complexes.

Cooperative spin crossover transitions with thermal hysteresis loops are rarely observed in cobalt(II) complexes. Herein, two new mononuclear cobalt(II) complexes with hysteretic spin crossover at relatively high temperatures (from 320 to 400 K), namely, [Co(terpy-CH2OH)2]·X2 (terpy-CH2OH = 4'-(hydroxymethyl)-2,2';6',2″-terpyridine, X = SCN-(1) and SeCN- (2)), have been synthesized and characterized structurally and magnetically. Both compounds are mononuclear CoII complexes with two chelating terpy-CH2OH ligands. Magnetic measurements revealed the existence of the hysteretic SCO transitions for both complexes. For compound 1, a one-step transition with T1/2↑= 334.5 K was observed upon heating, while a two-step transition is observed upon cooling with T1/2↓(1) = 329.3 K and T1/2↓(2) = 324.1 K (at a temperature sweep rate of 5 K/min). As for compound 2, a hysteresis loop with a width of 5 K (T1/2↓ = 391.6 K and T1/2↑ = 396.6 K, at a sweep rate of 5 K/min) can be observed. Thanks to the absence of the crystallized lattice solvents, their single crystals are stable enough at high temperatures for the structure determination at both spin states, which reveals that the hysteretic SCO transitions in both complexes originate from the crystallographic phase transitions involving a thermally induced order-disorder transition of the dangling -CH2OH groups in the ligand. This work shows that the modification of the terpy ligand has an important effect on the magnetic properties of the resulting cobalt(II) complexes.

Lattice dynamics and phase transitions in FAPbBr3 single crystals: Temperature‐ and pressure‐dependent Raman spectroscopy

AbstractThe rapidly emerging perovskites hold immense potential for revolutionizing optoelectronic and photovoltaic applications. However, understanding the complex structural dynamics and their response at extreme conditions in robust environments is crucial for optimizing the practical performance of perovskite‐based devices. Previous X‐ray diffraction studies have shown great potential for studying the average structures of these materials, but for more complex analysis at the local atomic level, Raman spectroscopy is a powerful tool. In this study, temperature‐ and pressure‐dependent Raman spectroscopy was used to elucidate the intricate lattice dynamics, phase transitions, and amorphization of FAPbBr3 single crystals at extreme conditions such as low temperature or high pressure. Temperature‐dependent Raman spectra unveiled significant variations in wavenumbers, full width at half maximum, and the vanishing of specific modes at higher temperatures. These were ascribed to symmetry changes caused by two crystallographic phase transitions at −127°C from orthorhombic to tetragonal and at −33°C from tetragonal to cubic phase. In addition, some of the Raman modes disappeared upon heating at −90°C, which was associated with a crystallographically unresolved transition. Pressure‐dependent Raman scattering revealed two phase transitions at 0.3 GPa and 2.2 GPa, which corresponded to the contraction of the PbBr6 octahedra and their tilting distortion, respectively. Further compression uncovered amorphization at 3.6 GPa, characterized by the vanishing of crystalline Raman modes together with the emergence of broad new modes due to the disorder within the crystal structure. Upon pressure release, the original Raman modes were recovered, indicating the reversibility of the pressure‐induced phase transitions. The changes in the Raman spectra were the most significant, especially in the low‐wavenumber lattice modes, when the FAPbBr3 underwent orthorhombic phase transition. It indicates that the inorganic sublattice is affected by the structural change into the orthorhombic phase caused either by temperature or pressure variation.

Theoretical and Experimental Advances in High-Pressure Behaviors of Nanoparticles.

Using compressive mechanical forces, such as pressure, to induce crystallographic phase transitions and mesostructural changes while modulating material properties in nanoparticles (NPs) is a unique way to discover new phase behaviors, create novel nanostructures, and study emerging properties that are difficult to achieve under conventional conditions. In recent decades, NPs of a plethora of chemical compositions, sizes, shapes, surface ligands, and self-assembled mesostructures have been studied under pressure by in-situ scattering and/or spectroscopy techniques. As a result, the fundamental knowledge of pressure-structure-property relationships has been significantly improved, leading to a better understanding of the design guidelines for nanomaterial synthesis. In the present review, we discuss experimental progress in NP high-pressure research conducted primarily over roughly the past four years on semiconductor NPs, metal and metal oxide NPs, and perovskite NPs. We focus on the pressure-induced behaviors of NPs at both the atomic- and mesoscales, inorganic NP property changes upon compression, and the structural and property transitions of perovskite NPs under pressure. We further discuss in depth progress on molecular modeling, including simulations of ligand behavior, phase-change chalcogenides, layered transition metal dichalcogenides, boron nitride, and inorganic and hybrid organic-inorganic perovskites NPs. These models now provide both mechanistic explanations of experimental observations and predictive guidelines for future experimental design. We conclude with a summary and our insights on future directions for exploration of nanomaterial phase transition, coupling, growth, and nanoelectronic and photonic properties.

Structural modulation and spin glassiness upon oxidation in oxygen storage material LnFeMnO4+x for Ln = Y, Lu, and Yb

The mixed valence multiferroic LnFe2+Fe3+O4 (where Ln = Y, Lu, and Yb) can reversibly uptake oxygen into its lattice, which is evidenced by a crystallographic phase transition along with the appearance of structural modulations. In this study, we show that the Mn-substituted version of this multiferroic can also be readily oxidized to LnFe3+Mn3+O4.5 revealing similar oxygen storage behavior. Through neutron, electron, and synchrotron x-ray diffraction studies, we observe a structural modulation that we attribute to a displacement wave in the fully oxidized compound. This wave exhibits commensurability with a wavevector q = (−2/7, 1/7, 0). Bond valence summation analysis of plausible interstitial oxygen positions suggests that oxygen insertion likely occurs at the middle of the Fe/Mn–O bipyramid layers. The structural modulation of LnFeMnO4.5 is two-dimensional, propagates along the ab-plane, and is highly symmetric as 12 identical modulation vectors are observed in the diffraction patterns. The nature of the lanthanide, Ln3+, does not seem to influence such modulations since we observe identical satellite reflections for all three samples of Ln = Y, Lu, and Yb. Both LnFeMnO4 and LnFeMnO4.5 display spin glassy behavior with 2D short-range magnetic ordering being observed in LnFeMnO4. Analysis of the neutron diffraction data reveals a correlation length of ∼10 nm. Upon oxidation to LnFeMnO4.5, the short-range magnetic order is significantly suppressed.

Order-Disorder, Symmetry Breaking, and Crystallographic Phase Transition in a Series of Bis(trans-thiocyanate)iron(II) Spin Crossover Complexes Based on Tetradentate Ligands Containing 1,2,3-Triazoles.

We report herein a series of neutral trans-thiocyanate mononuclear spin crossover (SCO) complexes, [FeIIL(NCS)2] (1-4), based on tetradentate ligands L obtained by reaction of N-substituted 1,2,3-triazolecarbaldehyde with 1,3-propanediamine or 2,2-dimethyl-1,3-diaminopropane [L = N1,N3-bis((1,5-dimethyl-1H-1,2,3-triazol-4-yl)methylene)propane-1,3-diamine/-2,2-dimethylpropane-1,3-diamine, 1/2 and N1,N3-bis((1-ethyl/1-propyl-1H-1,2,3-triazol-4-yl)methylene)-2,2-dimethylpropane-1,3-diamine, 3/4]. The thermal-induced SCO behavior is characterized by abrupt transitions with an average critical temperature (ΔT1/2)/hysteresis loop width (ΔThyst) in the range 190-252/5-14 K, while the photo-generated metastable high-spin (HS) phases are characterized by TLIESST temperatures in the range 44-59 K. Single crystal analysis shows that except 1, all compounds experience reversible symmetry breaking coupled with the thermal SCO. Furthermore, 4 experiences an additional phase transition at ca. 290 K responsible for the coexistence of two HS phases quenched at 10 K through LIESST and TIESST effects. The molecules form hexagonally packed arrays sustained by numerous weak CH···S and C···C/S···C/N···C bonds involving polar coordination cores, while non-polar pendant aliphatic substituents are segregated inside, occupying hexagonal channels. Energy framework analysis of complexes with one step SCO transition (1, 2, and 4) shows a correlation between the cooperativity and the amplitude of changes in the molecule-molecule interactions in the lattice at the SCO transition.

Assessment of shock wave assisted crystallographic structural stability of poly-crystalline and single crystalline lithium sulfate monohydrate crystals

In the present work, we demonstrate the interesting findings of shock wave recovery experiment conducted on poly-crystalline lithium sulfate monohydrate crystals (Li2SO4.H2O) under 50 and 100 shock pulses loaded conditions and the obtained results are compared to the obtained results of single crystal Li2SO4.H2O. The poly-crystalline Li2SO4.H2O samples neither undergo any crystallographic phase transitions nor shock wave assisted dehydration. But, the attained diffraction and Raman results indicate that, at shock loaded conditions, lots of structural deformation and distortions occur in the mother crystal structure by the impact of shock waves. Also, at shocked conditions, the super-paramagnetic state of Li2SO4.H2O is significantly affected and remarkable reduction (10–1 to 10–7) of the saturation magnetization is found. Note that, in the case of single crystalline Li2SO4.H2O, the disordered crystal structure has been witnessed for shock loaded samples.

Shock wave recovery experiments on poly-crystalline tri-glycine sulfate – X-ray and Raman analyses

Recent reports of shock wave experiments on non-linear optical (NLO) crystals have demonstrated outstanding results. Suitable candidates are currently being studied for industrial applications. For the present experiment, we have chosen tri-glycine sulfate (TGS) for the investigation of the structural properties after shock wave loaded conditions by employing X-ray diffraction and Raman spectroscopic measurements. The observed diffraction and spectroscopic patterns of the test polycrystalline sample reveal that the test sample does not undergo any crystallographic phase transition. But, there are several additional shoulder peaks observed and Raman measurements show that a few Raman bands appear while some disappear by the impact of shock waves due to the re-orientational effect of glycine molecules. The observed interesting results are discussed.

SYNTHESIS AND INVESTIGATION OF ELECTROCHEMICAL CHARACTERISTICS OF OXIDE Li-CONDUCTIVE MATERIALS WITH SPINEL AND PEROSKITE STRUCTURES

Lithium-ion batteries (LIBs) are widely used in electronic devices due to their numerous advantages, namely high energy density, high capacity, and long service life. One of the important components of a battery is the anode. In order to ensure high characteristics of LIB, the anode material must have high capacity, high ionic and electronic conductivities, and low cost. However, commonly used anode materials in lithium-ion batteries have a number of disadvantages. For example, a graphite-based anode is characterized by significant changes in volume during intercalation/deintercalation of lithium ions, high energy losses, and rapid deterioration of characteristics at high discharge/charge rates; Li4Ti5O12 have a low theoretical specific capacity, low electronic conductivity and low diffusion rate of lithium ions.&#x0D; Thus, the search for anode materials with high capacity and capability rate, as well as small volume change during lithium intercalation/deintercalation, remains an urgent task. A promising way may be the use of materials with intercalation pseudocapacitive behavior of charge accumulation, which occurs due to the intercalation of ions in tunnels or layers of active materials without a crystallographic phase transition. LixLa2/3-x/3TiO3 is well known as a superionic conductor with a high ionic conductivity σ ≈ 10–3 S/cm at room temperature. It crystallizes in a perovskite-type structure that consists of a framework of TiO6 octahedra stabilized by La atoms, and has nume­rous vacancies in the unoccupied positions 18d and 6a, that could participate in the stora­ge and motion of Li ions.&#x0D; Electrochemical characteristics of LixLa2/3-x/3TiO3 (x = 0.35 and 0.5) anode materials with a perovskite structure were investigated and compared with the electrochemical characteristics of Li4Ti5O12 with a layered spinel structure.

Variation of structural and magnetic properties of mixed-valent manganites through A-site cationic ordering

Effect of A-site cationic ordering on structural, transport and magnetic properties of mixed-valent perovskite manganite NdBaMn2O6 has been studied. Three samples of same chemical composition NdBaMn2O6 but with different degrees of A-site ordering (92 %, 60 %, 28 %) were prepared by tuning the synthesis conditions. At higher temperatures, all the compounds possess the same crystallographic phase (P4/mmm). However, temperature (T) dependent X-ray diffraction data reveals that different types of crystallographic phase transitions depends on the degree of ordering of the A-site cations Nd3+ and Ba2+. For example, the maximum ordered compound undergoes multiple structural phase transitions (from P4/mmm to Cmmm to P21am) with decreasing T, whereas the disordered compound retains the high-T crystal structure (P4/mmm) throughout the studied temperature range. Resistivity measurements shows that although both the compounds (ordered and disordered) are insulating, the mechanism of charge transport is different for the two compounds. Similarly the magnetic properties and colossal magnetoresistance also depend on the degree of ordering. Cationic disorder suppresses the long-range antiferromagnetic order and enhances ferromagnetic correlations at lower temperature; which (ferromagnetic correlation) is accompanied with larger value of saturation magnetic moment while ferromagnetic TC too shifts to higher temperature with increasing disorder. Disordered system also exhibits a larger value of magnetoresistance at low temperature compared to the ordered counterpart.

Structural and morphological behaviours of l-Asparagine monohydrate at shocked conditions

Studies on the dynamic shock impact on solids also provide a magnificent scope of understating the stability of materials that are needed for high-pressure applications. Based on the impending investigations arising out of the observed experimental results of the shock-wave impact on solids, it is very much revealed that the impact of shock waves on molecular crystals is not yet well understood; especially amino acid crystals. Hence the present work deals with the assessment of crystallographic phase stability of l-Asparagine monohydrate (C4H8N2O3·H2O) amino acid powder samples against shocked-conditions and the results have been analyzed by X-ray powder diffractometry and scanning electron microscopy. The results of XRD and SEM reveal that the mother crystallographic phase of the title sample has significantly changed without inducing any crystallographic phase-transition and the observed structural modifications are discussed on the basis of previous publications reported on the static high-pressure study on the title sample.

Role of phonon mode in the enhancement of ferroelectric polarization in a perovskite-based eco-friendly functional material

We report here the role of component freezing of three-dimensional polar () phonon mode corresponding to the center of cubic Brillouin zone in tuning the structure-property correlations of a scientifically enriched and technologically important barium-titanate–based eco-friendly functional material (Ba0.92Ca0.08)(Zr0.05Ti0.95−x Sn x )O3; BCZTSnx synthesized via solid-state reaction method. The combined X-ray diffraction, Raman spectroscopic analysis, and temperature-dependent dielectric studies have revealed the presence of several crystallographic phase transitions with coexisting phases, viz., , as a function of Sn(x) content. These crystallographic phases, viz., P4mm, Amm2, and R3m results due to freezing of the component(s) of phonon mode (belonging to space group), with the respective order parameter directions (0,0,a), (a,a,0), and (a,a,a) leading to ferroelectric polarization along , and directions, respectively. The ceramic composition corresponding to exhibits a significant reduction in the coercive field (E c ) and an enhancement in ferroelectric polarization (P r ) in comparison to , inferred from PE loop measurements. The enhancement in ferroelectric polarization at has been attributed to the inter-ferroelectric three-phase coexistence around this composition and significantly enhanced amplitudes of ferroelectric phonon modes corresponding to orthorhombic and rhombohedral phases, calculated using the symmetry mode analysis technique. The existence of a high ferroelectric polarization and low coercive field may lead to composition as an eco-friendly candidate for ferroelectric memory devices.

Metal-organic framework-derived mixed-phase anatase/rutile TiO2 towards boosted lithium storage: Surface engineering and design strategy through crystal phase transition

The design and construction of electrodes with surface and interface structures bring new opportunities for high-performance lithium storage properties. Herein, we present a simple synthesis method to fabricate surface-amorphized anatase/rutile mixed-phase truncated octahedral TiO2 (TO-AR) structures with oxygen vacancy derived from metal-organic framework (MOF) with a temperature-controlled phase transition. Compared with single-phase TiO2, the mixed-phase TO-AR electrode shows higher specific capacity and better rate performance. Systematic experimental studies and theoretical calculations demonstrate that the abundant interface between anatase and rutile induced by the crystallographic phase transition provides efficient high-capacity Li+ storage and enhanced charge-transfer kinetics. Meanwhile, the amorphous surface and higher oxygen vacancy concentration improve the surface-induced capacitive properties. These results provide new insights into improving the electrochemical performance of metal-organic framework-derived anode materials in Li-ion batteries.

Structural phase transition and variation of magnetoresistance in the stoichiometric double perovskite Sr2−yNdyFe1+xMo1−xO6 (0.05 ≤ y ≤ 0.45 and x = y/2)

The interplay between magnetic, megneto-transport and structural properties of Nd-doped double perovskite Sr2−yNdyFe1+xMo1−xO6, in the range 0.05 <y ​< ​0.45 for x ​= ​y/2 and synthesized by solid state reaction, has been investigated. Specifically, it has been shown that the observed tetragonal to monoclinic crystallographic phase transition at the Nd composition in the range y ​= ​0.10 to y ​= ​0.15 is in close relationship with its magnetic and magnetoresistive behavior. The observed crystallographic transition, confirmed by X-ray diffraction experiments, is consistent with the decrease of the unit cell volume when the Nd doping content increases. Besides, the Curie temperature determined by thermogravimetric experiments increases with the Nd content just after the structural transition. Furthermore, the increase of Nd doping up to y ​= ​0.45 in the double perovskite structure leads to a magnetization loss about 98% as a result of the increase of both, anti-site defects and the number of charge carriers. The progressive magnetization loss with Nd doping is also responsible for the observed monotonic decrease of the magnetoresistance ratio due to the predominance of the antiferromagnetic order. Particularly, the electrical behavior in the vicinity of the crystallographic transition is characterized by a very slight increase followed by a rapid drop of the magnetoresistance ratio, which is originated by the corresponding fluctuations of the saturation magnetization.

High temperature crystallographic and low temperature magnetic phase transitions in Fe doped Sr2RuMnO6

Fe doped Sr2RuMnO6 (SRMO) double perovskites (Sr2RuMn1-xFexO6, x = 0, 0.1, 0.2 and 0.3) were prepared by solid-state route. Both x-ray diffraction and Raman spectroscopy were performed to investigate the crystal structure of the synthesized double perovskites. Rietveld refinement of the x-ray diffraction patterns confirmed a phase transition from tetragonal to cubic space group as a function of doping concentration of iron. Raman spectroscopy at room temperature and group theory analysis revealed the phonon modes associated with the space group of the samples. The temperature dependent Raman spectroscopy showed an anharmonic behaviour of the phonon modes of the Fe doped SRMO samples. The temperature evolution of the phononic modes in the range of 300 K–620 K is predominantly influenced by the lattice degrees of freedom. The presence of several oxidation states Mn (2+, 3+ and 4+) and Fe (3+ and 4+) was confirmed by an X-ray photoemission spectroscopy analysis of the highest doped sample (x = 0.3). The magnetic properties measurements showed that the samples were completely paramagnetic at room temperature. The samples exhibit antiferromagnetism at very low temperatures and we conclude that they exhibit ferrimagnetic ground state in the mid temperature region.