Floating Zone Furnace Research Articles

Growth and characterization of perovskite TbMnO3 single crystal: Structural, vibrational and magnetic properties

In this study, we have successfully grown a high-quality single crystal of perovskite TbMnO3 utilizing an optical floating zone furnace under an air atmosphere. To ensure the crystal purity and orientation, we probed X-ray diffractometer (XRD) and X-ray Laue photographic analysis, respectively. The XRD analysis confirmed that TbMnO3 ceramics possess a distorted orthorhombic perovskite structure (Pbnm). By analyzing the X-ray absorption and vibrational modes via Raman spectroscopy, we not only confirmed the pure phase of the TbMnO3 sample but also gained valuable insights. In terms of magnetic properties, we conducted measurements in two different orientations: H||a and H||c. Notably, there were no successive transitions observed along the H||a direction, but along H||c, we observed three successive transitions with decreasing temperature at TN = 41 K, TS = 28 K, and TNTb = 7 K. Below TN (41 K), there is an unusual softening observed in one of the first order phonon modes, indicating a robust connection between spin and phonon interactions. The magnetic phase transition along both axes validates the presence of magnetic anisotropy in the prepared single crystal, as indicated by magnetic susceptibility. The negative θcw value along the a-axis and the positive θcw value along the c-axis suggest a competition between antiferromagnetic and ferromagnetic interactions in the ac-plane.

Advances in high-pressure laser floating zone growth: The Laser Optical Kristallmacher II (LOKII).

The optical floating zone crystal growth technique is a well-established method for obtaining large, high-purity single crystals. While the floating zone method has been constantly evolving for over six decades, the development of high-pressure (up to 1000bar) growth systems has only recently been realized via the combination of laser-based heating sources with an all-metal chamber. While our inaugural high-pressure laser floating zone furnace design demonstrated the successful growth of new volatile and metastable phases, the furnace design faces several limitations with imaging quality, heating profile control, and chamber cooling power. Here, we present a second-generation design of the high-pressure laser floating zone furnace, "Laser Optical Kristallmacher II" (LOKII), and demonstrate that this redesign facilitates new advances in crystal growth by highlighting several exemplar materials: α-Fe2O3, β-Ga2O3, and La2CuO4+δ. Notably, for La2CuO4+δ, we demonstrate the feasibility and long-term stability of traveling solvent floating zone growth under a record pressure of 700bar.

Magnetic-field-induced spin reorientation in TmFeO<sub>3</sub> single crystals

TmFeO<sub>3</sub> exhibits rich physical properties such as magneto-optical effect, multiferroicity, and spin reorientation, making it possess significant research value in condensed matter physics and materials science. In this study, we utilize a time-domain terahertz magneto-optical spectroscopy system to investigate the changes in spin resonance frequency of TmFeO<sub>3</sub> single crystal at <i>T</i> = 1.6 K under external magnetic fields in a range of 0–7 T. The TmFeO<sub>3</sub> sample is grown in an optical floating zone furnace and its crystallographic orientation is determined by using back-reflection Laue X-ray photography with a tungsten target. The measurement setup is a self-built time-domain terahertz magneto-optical spectroscopy system, with magnetic fields in a range of 0–7 T, temperatures in a range of 1.6–300 K, and a spectral range of 0.2–2.0 THz. A pair of 1 mm-thick ZnTe nonlinear crystals is used to generate and detect terahertz signals through optical rectification and electro-optic sampling technique. The system variable temperature and magnetic field are controlled by a superconducting magnet. In experiments, a linearly polarized terahertz wave is vertically incident on the sample surface, and its magnetic component <i>H</i><sub>THz</sub> is parallel to the sample surface. By rotating the sample, the angle (<i>θ</i>) between macroscopic magnetic moment <i> <b>M</b> </i> and <i>H</i><sub>THz</sub> can be tuned, achieving selective excitations of the two modes, that is, <i>θ</i> = 0 for q-AFM mode and 90° for q-FM mode. Terahertz absorption spectrum results indicate that as the magnetic field increases, the quasi-ferromagnetic resonance (q-FM) of TmFeO<sub>3</sub> single crystal shifts towards high frequencies, and quasi-antiferromagnetic resonance (q-AFM) transits to q-FM under low critical magnetic fields (2.2–3.6 T). Through magnetic structure analysis and theoretical fitting, it is confirmed that the magnetic moment of the single crystal undergoes magnetic field induced spin reorientation. This study is helpful in better understanding of the regulation mechanism of the internal magnetic structure of rare earth ferrite under the combined action of external magnetic field and temperature field, and also in developing related spin electronic devices.

Effects of pressure and doping on Ruddlesden-Popper phases Lan+1NinO3n+1

Recently, the discovery of superconductivity with a critical temperature Tc up to 80 K in Ruddlesden–Popper phases Lan+1NinO3n+1 (n = 2) under pressure has garnered considerable attention. Up to now, the superconductivity was only observed in La3Ni2O7 single crystal grown with the optical-image floating zone furnace under oxygen pressure. It remains to be understood the effect of chemical doping on superconducting La3Ni2O7 as well as other Ruddlesden–Popper phases. Here, we systematically investigate the effect of external pressure and chemical doping on polycrystalline Ruddlesden–Popper phases. Our results demonstrate that the application of pressure and doping effectively tunes the transport properties of Ruddlesden–Popper phases. We find pressure-induced superconductivity up to 86 K in La3Ni2O7 polycrystalline sample, while no signatures of superconductivity are observed in La2NiO4 and La4Ni3O10 polycrystalline samples under high pressure up to 50 GPa. Our study sheds light on the exploration of high-Tc superconductivity in nickelates.

Crystal Growth of the R2SiO5 Compounds (R = Dy, Ho, and Er) by the Floating Zone Method Using a Laser-Diode-Heated Furnace

In recent years, rare earth silicate compounds have attracted the extensive attention of researchers owing to their potential for applications in scintillation crystals in gamma ray or X-ray detectors, as well as in thermal or environmental barrier coatings. Large high quality crystals of three members of the rare earth monosilicates family of compounds, R2SiO5 (with R = Dy, Ho, and Er), have been grown by the floating zone method, using a laser-diode-heated floating zone furnace. Crystal growths attempts were carried out using different parameters in order to determine the optimum conditions for the growth of these materials. The phase purity and the crystalline quality of the crystal boules were analysed using powder and Laue X-ray diffraction. Single crystal X-ray diffraction experiments were carried out to determine the crystal structures of the boules. The optimum conditions used for the crystal growth of R2SiO5 materials are reported. The phase purity and high crystalline quality of the crystals produced makes them ideal for detailed investigations of the intrinsic physical and chemical properties of these materials.

Optical and scintillation properties of the Eu2O3-doped HfO2-Al2O3–SiO2 glass ceramics

In this study, Eu-doped 10HfO2–10Al2O3–80SiO2 glass ceramics with different Eu concentrations were prepared by the melt-quenching method using an optical floating zone furnace, and optical and scintillation properties were investigated to apply them for radiation detectors. All the glass ceramic samples were transparent, although they included not only an amorphous phase but also a crystal phase of cubic-HfO2. Photoluminescence and scintillation peaks due to Eu2+ were detected at 400–550 nm. In the glass ceramic samples with higher Eu concentration, the luminescence of Eu3+ was also observed. Quantum yields and afterglow levels decreased with increasing Eu concentration. The 1.0% Eu-doped sample had the highest light yield among all our glass samples, and the light yield was 630 photons/MeV under γ-ray irradiation from 137Cs.

Emergence of High-Temperature Superconducting Phase in Pressurized La3Ni2O7 Crystals

The recent report of pressure-induced structural transition and signature of superconductivity with T c ≈ 80 K above 14 GPa in La3Ni2O7 crystals has garnered considerable attention. To further elaborate this discovery, we carried out comprehensive resistance measurements on La3Ni2O7 crystals grown in an optical-image floating zone furnace under oxygen pressure (15 bar) using a diamond anvil cell (DAC) and cubic anvil cell (CAC), which employ a solid (KBr) and liquid (glycerol) pressure-transmitting medium, respectively. Sample 1 measured in the DAC exhibits a semiconducting-like behavior with large resistance at low pressures and gradually becomes metallic upon compression. At pressures P ⩾ 13.7 GPa we observed the appearance of a resistance drop of as much as ∼ 50% around 70 K, which evolves into a kink-like anomaly at pressures above 40 GPa and shifts to lower temperatures gradually with increasing magnetic field. These observations are consistent with the recent report mentioned above. On the other hand, sample 2 measured in the CAC retains metallic behavior in the investigated pressure range up to 15 GPa. The hump-like anomaly in resistance around ∼ 130 K at ambient pressure disappears at P ⩾ 2 GPa. In the pressure range of 11–15 GPa we observed the gradual development of a shoulder-like anomaly in resistance at low temperatures, which evolves into a pronounced drop of resistance of 98% below 62 K at 15 GPa, reaching a temperature-independent resistance of 20 μΩ below 20 K. Similarly, this resistance anomaly can be progressively shifted to lower temperatures by applying external magnetic fields, resembling a typical superconducting transition. Measurements on sample 3 in the CAC reproduce the resistance drop at pressures above 10 GPa and realize zero resistance below 10 K at 15 GPa even though an unusual semiconducting-like behavior is retained in the normal state. Based on these results, we constructed a dome-shaped superconducting phase diagram and discuss some issues regarding the sample-dependent behaviors on pressure-induced high-temperature superconductivity in the La3Ni2O7 crystals.

Tunable magnetic phase transition in thulium–samarium orthoferrite single crystals

Spintronics and condensed matter physics are in pursuit of materials that can serve as carriers for novel quantum devices. Antiferromagnetic rare earth orthoferrites (RFeO3, where R is rare earth or Y), are potential functional materials for magnetic information processing. They exhibit temperature-controlled spin reorientation transition (SRT) and magnetic field/temperature-induced spin switching (SSW) properties. As such, RFeO3 is expected to be used in spintronic devices that can easily control the spin. With the advancement of research, the co-doping of rare earth ions has emerged as a prominent area of investigation in RFeO3. In this work, we have grown a series of Tm1-xSmxFeO3 (TSFO, x = 0, 0.2, 0.3, 0.4) single crystals via a four-mirror optical floating zone furnace. Crystal axes and single phase of these single crystals were determined using Laue back reflection camera and X-ray diffractometer. We observed that the doping of Sm ions can effectively regulate the spin reorientation temperature of the parent material TmFeO3. Both type-I and type-II SSW have been observed when the doping rate x is 0.2 or 0.4, perfectly integrating the magnetic properties of TmFeO3 and SmFeO3 single crystals. Furthermore, the spin switching in TSFO (x = 0.2, 0.3, 0.4) can be manipulated by applying low magnetic fields with tens of Oe. On the other hand, when the doping rate x reaches 0.4, the magnetic compensation phenomenon and the Néer temperature of rare earth ions occurred. The super-exchange interaction between R3+ and Fe3+ magnetic sublattices leads to these interesting phenomena.

The surface tension of Ga2O3 melt measured by a drop-weight method in an optical floating-zone furnace

The surface tension of Ga2O3 melt is successfully measured using a drop-weight method in an optical floating-zone furnace that we have developed. The method is verified to be feasible by measuring the surface tension value of TiO2 melt and then comparing it with values in previous reports determined by other methods. We find that the surface tension of Si-doped Ga2O3 melt increases with the decrease in the Si doping concentration and reaches 527.9 mN m−1 for pure Ga2O3 melt. The surface tension of the unintentionally doped Ga2O3 melt is also measured to be 519.3 mN m−1 in the presence of some common contaminants appearing in Czochralski and edge-defined film-fed growth methods, including Ir, Al, and Si.

Low field spin switching of single crystal TmFeO3

High quality TmFeO3 single crystal with the length of 50 mm has been prepared by using a four-mirror optical floating zone furnace. X-ray diffractometer and Laue back reflection camera are used to determine the quality and crystal orientations of TmFeO3 single crystal. Here, the magnetic properties of TmFeO3 single crystal in low magnetic fields are studied systematically. A typical spin reorientation transition from Γ4(Gx, Ay, Fz) configuration to Γ2(Fx, Cy, Gz) configuration is observed in TmFeO3 single crystal with the temperature between 82 K and 95 K. Temperature-induced type-II spin switching in both a-axis and c-axis are observed in field cooling and measuring while cooling (FCC) and field cooled and measuring while warming (FCW) modes, which has not been reported in previous researches on TmFeO3 single crystal. This is an extremely rare occurrence within the RFeO3 family. The results suggest that such spin switching is easily susceptible to very low external magnetic fields. Therefore, by adjusting the magnitude of the external magnetic fields, the triggering temperatures of spin switching can be controlled, which offers the possibility of the application for TmFeO3 single crystal in future spintronic devices.

Ordered and disordered variants of the triangular lattice antiferromagnet Ca3NiNb2O9 : Crystal growth and magnetic properties

Single crystals of the triangular lattice antiferromagnet (TLAF) ${\mathrm{Ca}}_{3}{\mathrm{NiNb}}_{2}{\mathrm{O}}_{9}$ and its nonmagnetic analog ${\mathrm{Ca}}_{3}{\mathrm{MgNb}}_{2}{\mathrm{O}}_{9}$ are grown using the four-mirror optical floating-zone furnace. By varying the growth conditions, two types of mm-sized crystals are obtained: monoclinic crystals of the form ${\mathrm{Ca}}_{3}{\mathrm{NiNb}}_{2}{\mathrm{O}}_{9}$ where ${\mathrm{Ni}}^{2+}$ and ${\mathrm{Nb}}^{5+}$ exhibits 1:2 ordering and Ni ions (spin 1) are arranged on a triangular lattice, and orthorhombic crystals of the form ${\mathrm{CaBO}}_{3}$ where B site is occupied randomly by 1/3 Ni and 2/3 Nb. Low-temperature specific heat and low-field magnetization on these crystal modifications revealed contrasting ground states. In B-site ordered ${\mathrm{Ca}}_{3}{\mathrm{NiNb}}_{2}{\mathrm{O}}_{9}$, the Ni spins undergo two successive phase transitions at ${\mathrm{T}}_{{\mathrm{N}}_{1}}=4.6\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and ${\mathrm{T}}_{{\mathrm{N}}_{2}}=4.2\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. The magnetic propagation vector below ${\mathrm{T}}_{{\mathrm{N}}_{2}}$ is found to be $\stackrel{P\vec}{k}=(0,1/3,0)$ confirming the ${120}^{\ensuremath{\circ}}$ spin structure. The high-field magnetization reveals the presence of plateaus characteristic of TLAFs. In contrast, the orthorhombic ${\mathrm{CaBO}}_{3}$ crystals exhibit a spin-glass-like ground state.

Effect of Tm doping on photoluminescence, scintillation, and thermally stimulated luminescence properties of MgAl2O4 single crystals

The Tm-doped MgAl2O4 single crystals were synthesized by using Xe arc lamps-equipped floating zone furnace. The synthesized crystals exhibited luminescence due to the 4f-4f transitions of Tm3+ in photoluminescence (PL), scintillation, and thermally stimulated luminescence (TSL). In all of PL, scintillation, and TSL, the 0.5% Tm-doped crystal showed the highest luminescence intensity. In TSL dose response functions, the 0.5% Tm-doped crystal showed sensitivity from X-ray irradiation with 0.1 mGy. In addition, we measured linear energy transfer (LET) dependence on TSL glow curve of the crystal and X-ray imaging test taken by TSL. We revealed the spatial resolution of the crystal was 100 μm.

Microstructures and mechanical properties of V–V3Si eutectic composites

Abstract V–V3Si eutectic alloys were directionally solidified in a high temperature optical floating zone furnace. Depending on the solidification conditions, several microstructures were observed, such as well-aligned broken lamellar, fibrous, or cellular microstructures. The interphase spacings increased with decreasing solidification rates in agreement with the Jackson-Hunt theory. The mechanical properties of the individual phases were investigated by nanoindentation. It was found that the modulus and nanoindentation hardness of V3Si are 214 and 13.8 GPa, respectively, and those of the V solid-solution are 165 and 3.4 GPa, respectively. The high-temperature strength was examined by tensile testing at elevated temperatures. Preliminary results show that the ductile-to-brittle transition temperature is about 800 °C for this composite, and its strength is significantly higher than conventional V solid-solution alloys.

Determination of the Partial Contributions to the Electrical Conductivity of TiO2-SiO2-Al2O3-MgO-CaO Slags: Role of the Experimental Processing Conditions

The electrical transport properties of molten TiO2–SiO2–Al2O3–MgO–CaO slags were determined as a function of temperature and oxygen partial pressure. To avoid the corrosion of crucible materials by this slag at ultra high temperatures, the pendant droplet technique was used inside a modified floating zone furnace. Electronic and ionic transference numbers were estimated using stepped-potential chronoamperometry experiments to quantify the contribution of the electronic/ionic conductivity to the total electric conductivity. The results show that these slags are mixed conductors, where current is carried by ionic and electronic carriers. The oxygen partial pressure dependence of the electronic transference numbers, t_e, indicated a semiconducting mechanism in the molten slag. The ratio of the different valences of the transition metal ions had a predominant effect on the t_e. The {{text{TiO}}_{2}} content also favoured electronic conduction, while the effect of temperature and structure was less noticeable within the temperature and composition range studied.

Compositional screening of Ce-doped (Gd,Lu,Y)3(Al,Ga)5O12 ceramics prepared by quenching from melt and their luminescence properties

Quenching from the melt using an Optical Floating Zone furnace was investigated as a possible high-throughput preparation method in order to screen novel scintillating materials. To validate this method, polycrystalline rare-earth aluminum garnets and yttrium gallium aluminum garnets were synthesized and characterized by X-ray diffraction, photoluminescence and radioluminescence emission spectra as well as radioluminescence imaging and compared to the previously reported properties of those materials. In order to achieve rapid, but quantitative comparison of the materials, pellets fabricated from the synthesized powders were sintered; two different sintering conditions were investigated and compared. A simplistic energy deposition and light absorption model for brightness of opaque samples under X-ray irradiation was developed to estimate the relative scintillation efficiency of the materials. Based on the results, Y3Al5O12, LuY2Al5O12 and GdY2Al5O12 seem to have the highest scintillation efficiency among the prepared samples.

Directionally solidified Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic high-entropy oxide ceramics with well-oriented structure, high hardness, and low thermal conductivity

Directionally solidified Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic high-entropy oxide ceramics (HEOCs) were successfully prepared with an optical floating zone furnace. The Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic HEOCs were pure phases with uniform distribution of rare-earth elements. The preferred growth orientation relationships were <10−10 > {0001}Al2O3 // <110 > {211}(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12. The indentation fracture toughness and Vickers hardness were 6.8 ± 0.9 MPa·m1/2 and 16.1 ± 0.3 GPa, which were higher than that of Al2O3/Y3Al5O12 eutectic ceramics. The room temperature bending strength was 333 ± 42 MPa. Crack bridging, deflection and bifurcation were the main toughening mechanism. Hardness and reduced modulus mapping results illustrated that the hardness of (Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 was close to that of Al2O3. Thermal expansion coefficient of Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic HEOCs was very similar to that of Al2O3/Y3Al5O12 but thermal conductivity was as low as 4.9 Wm−1 K−1 due to strong lattice distortion. These results suggest that high-entropy Al2O3/(Y0.2Er0.2Yb0.2Ho0.2Lu0.2)3Al5O12 eutectic ceramics are promising candidates for structural components application in gas turbine engines.

4f-3d interaction dominated field tailoring spin switching in rare earth doped Dy0.5Er0.5FeO3 single crystal

A large single crystal Dy0.5Er0.5FeO3 of 5.2 mm in diameter and 55 mm in length is prepared using the optical floating zone furnace system. The good quality of the single crystal without impurities is confirmed by powder and Laue X-ray diffraction experiments. Magnetic measurements are conducted using 1~2 millimeter cubic sample of Dy0.5Er0.5FeO3 single crystal, which experiences spin switching in two measurement modes of zero-field-cooling (ZFC) and field-cooling (FC) magnetization vs temperature (M-T) curves under magnetic fields less than 48 Oe. The co-occurrence of spin switching (i.e. magnetization drop in FC mode and magnetization jump in ZFC mode) has not been reported in the parent materials of DyFeO3 and ErFeO3 single crystals. More interestingly this kind of spin switching can be easily tailored by using low fields in a large temperature range from below 50 K to nearly 400 K. Spin reorientation transition occurs near 35.9-48 K, where the spin configuration of the iron sublattice changes from Γ4 and Γ2. The magnetic interaction between (Dy, Er)-4f and Fe-3d electrons in the two different sublattices of Dy0.5Er0.5FeO3 single crystal which governs the spin reorientation transition and spin switching under different temperature and magnetic field are discussed.

Automated extraction of physical parameters from experimentally obtained thermal profiles using a machine learning approach

Computational modeling is playing an increasingly important role in designing novel experiments and enhancing existing ones. However, these models require input parameters that are sufficiently accurate in order for the predictions to be quantitatively reliable. Frequently, some of these parameters are not directly measurable or have a large uncertainty. We propose a machine learning approach to automatically extract these uncertain or unknown parameters indirectly from experimental measurements that depend on the combination of parameters in a complex manner. The algorithm iteratively refines the possible range of each parameter based on the mean and standard deviation of the sampling simulations that are at the 10th percentile or lower in error until the convergence criteria is met, which is followed by a multivariate quadratic fit and minimization. To demonstrate its applicability, we apply the algorithm to determine physical parameters during the fitting of temperature profiles extracted from in situ synchrotron measurements of an optical floating zone furnace used for high-temperature crystal growth. We built a thermal transfer model in COMSOL Multiphysics® software that considers an Al2O3 sample that is heated by a power source and thermal conduction and cooled due to natural air convection and thermal radiation. A set of experimentally measured steady-state temperature profiles of a heated Al2O3 sample is used as training data to determine the parameter set using the algorithm, which resulted in a close match. Using this parameter set, we also simulated the time-dependent temperatures, which yielded good agreement to the corresponding experimental measurement. We conclude that the steady-state temperature profiles suffice as training data, eliminating the need for additional in situ measurements of the dynamic experimental state for robust model parameterization.

Characterization of high dense Pr:GdTaO4 crystal scintillators

Pr-doped GdTaO4 crystals with various Pr-concentrations were prepared using a floating zone furnace, and the photo- and radio-luminescence properties were evaluated. Pr:GdTaO4 exhibits photo- and radio-luminescence with several sharp emission peaks due to Pr3+. The decay time constants are in tens of μs order and monotonically decrease with dopant concentration, and the values are reasonable as that of the 4f–4f transitions of Pr3+. The pulse height distribution under 137Cs γ-ray irradiation demonstrates that the 0.5% Pr:GdTaO4 crystal shows the highest scintillation light yield of 5110 photons/MeV among the samples.

High oxygen pressure floating zone growth and crystal structure of the metallic nickelates R4Ni3O10 ( R=La,Pr )

Single crystals of the metallic Ruddlesden-Popper trilayer nickelates R$_4$Ni$_3$O$_{10}$ (R=La, Pr) were successfully grown using an optical-image floating zone furnace under oxygen pressure (pO$_2$) of 20 bar for La$_4$Ni$_3$O$_{10}$ and 140 bar for Pr$_4$Ni$_3$O$_{10}$. A combination of synchrotron and laboratory x-ray single crystal diffraction, high-resolution synchrotron x-ray powder diffraction and measurements of physical properties revealed that R$_4$Ni$_3$O$_{10}$ (R=La, Pr) crystallizes in the monoclinic $P$2$_1$/$a$ (Z=2) space group at room temperature, and that a metastable orthorhombic phase ($Bmab$) can be trapped by post-growth rapid cooling. Both La$_4$Ni$_3$O$_{10}$ and Pr$_4$Ni$_3$O$_{10}$ crystals undergo a metal-to-metal transition (MMT) below room temperature. In the case of Pr$_4$Ni$_3$O$_{10}$, the MMT is found at ~157.6 K. For La$_4$Ni$_3$O$_{10}$, the MMT depends on the lattice symmetry: 147.5 K for $Bmab$ vs. 138.6 K for $P$2$_1$/$a$. Lattice anomalies were found at the MMT that, when considered together with the pronounced dependence of the transition temperature on subtle structural differences between $Bmab$ and $P$2$_1$/$a$ phases, demonstrates a not insignificant coupling between electronic and lattice degrees of freedom in these trilayer nickelates.