arXiv subjects

Katharine Page

Publications and source records attributed to Katharine Page.

16 recordsLinked to original sources

arXiv2026

Synthesis and Characterization of Compositionally Complex (Gd/Ho/Er/Dy)2Zr2O7 Thin Film Combinatorial Library

High-throughput synthesis and characterization of novel ceramic materials with improved thermomechanical properties and phase stability are needed to accelerate the discovery of next-generation thermal barrier materials. A combinatorial thin film material library of (GdDyHoEr)2Zr2O7 were created via combinatorial magnetron reactive sputtering with rare-earth/zirconium alloy targets. Structural, chemical, and thermal property characterization mapping across the four component composition space was performed and correlated with thermal transport measurements. Steady state thermoreflectance mapping identifies a pronounced minimum in thermal conductivity within the Dy/Gd-rich quadrant. This minimum does not coincide with either the equiatomic composition or the region predicted to exhibit maximum cation size disorder. Instead, it corresponds to the largest experimentally observed lattice parameter, despite deviating from Vegard-like chemical averaging, and is independent of grain size and whole-pattern microstrain. These observations suggest that the way the fluorite lattice accommodates compositional complexity, rather than cation size disorder alone, provides a more informative descriptor of thermal transport. Overall, this work establishes a high-throughput workflow for combinatorial thin-film synthesis and multimodal characterization, enabling the rapid identification of previously inaccessible structure-property relationships in compositionally complex ceramics.

cond-mat.mtrl-sci↗

arXiv2026

SPEAR: Structure Property Explainability with Attention Regularization

Machine learning is increasingly used to learn structure property relationships from spectroscopic and diffraction data, yet its adoption in materials discovery is often limited by poor interpretability of model predictions. Although attention mechanisms are frequently treated as inherently explainable, unregularized attention can yield unstable, fragmented, or intensity driven attribution patterns that obscure the physical origin of these relationships. Here we introduce SPEAR (Structure Property Explainability with Attention Regularization), a framework that constrains attention distributions during training to improve their stability, selectivity, and physical interpretability. SPEAR augments attention based regression with a learnable temperature that controls attention concentration and a smoothness penalty that enforces coherence across neighboring spectral positions, treating attention as a learnable explanatory object rather than a post hoc visualization. Using synthetic spectral benchmarks with known generative structure, we show that attention regularization produces smooth, contiguous attribution profiles aligned with causal features while preserving predictive accuracy. Applied to experimental X ray diffraction data from a combinatorial rare earth zirconate thin film library, the regularized model selectively emphasizes physically relevant diffraction features and decouples feature importance from raw peak intensity. The reflection it identified prompted a reassessment of our earlier structural analysis, revealing a correlation between the 220 peak position, the tetragonal distortion that accommodates cation size disorder, and the local thermal conductivity. Attention regularization therefore provides a principled training constraint for explainable structure property regression, yielding mechanistically meaningful explanations without sacrificing predictive performance.

cond-mat.mtrl-sci↗

arXiv2026

Uncovering hidden bias in neutron diffraction residual strain measurements

When calculating residual strain via neutron or X-ray diffraction, uncertainties propagated from the peak fit are often inadequate to describe the true scatter of measurements about a singular strain state, such as one that should describe a macroscopic continuum. Because diffraction is inherently a selective process, orientation dependent scatter arises from the sub-sampling of strong microstructure and strain gradients. This paper investigates the appropriateness of propagated uncertainties with reference to their original intention, i.e., noise about a mean value. Thirty-six unique orientations of strain measurements are taken at multiple locations within an additive friction-stir deposition component with fine-scale gradients (~200 um) of plastic strain, texture, and residual elastic strain. Multiple strain and stress calculation pathways are compared: direct substitution of three measurements into Hooke's law, direct inversion of any six unique orientations into the strain state tensor, and thirty-six measurement least-squares estimation. For the latter two cases, the appropriateness of the uncertainty interval is statistically evaluated based on a physical constraint: common agreement under the strain transformation law. For this sample, the direct inversion of six measurements retains a conservative estimate of the uncertainty. However, propagated uncertainties in the least-squares solution greatly underestimate the true experimental scatter. A simple pathway to estimate appropriate uncertainty intervals is suggested. These results demonstrate that interpretation of uncertainty in residual strain is strongly dependent on intrinsic, sample-dependent effects, and that oversampling orientations and statistical analysis can give more accurate results with realistic uncertainties.

cond-mat.mtrl-sci↗

arXiv2026

diffpy.morph: Python tools for model independent comparisons between sets of 1D functions

diffpy$.$morph addresses a need to gain scientific insights from 1D scientific spectra in model independent ways. A powerful approach for this is to take differences between pairs of spectra and look for meaningful changes that might indicate underlying chemical, structural, or other modifications. The challenge is that the difference curve may contain uninteresting differences such as experimental inconsistencies and benign physical changes such as the effects of thermal expansion. diffpy$.$morph allows researchers to apply simple transformations, or "morphs", to one of the datasets to remove the unwanted differences revealing, when they are present, non-trivial differences. diffpy$.$morph is an open-source Python package available on the Python Package Index and conda-forge. Here, we describe its functionality and apply it to solve a range of experimental challenges on diffraction and PDF data from x-rays and neutrons, though we note that it may be applied to any 1D function in principle.

physics.comp-ph↗

arXiv2025

Exploring the Complex Landscape of Entropy Stabilized Oxides

Entropy-stabilized oxides (ESOs), driven by high configurational entropy, have gained phenomenological research interest due to their potential for tailoring structure property relationships. However, the chemical short range ordering (SRO) and its interplay with local lattice distortion (LD) remain to be explored, although they could diminish the configurational entropy and potentially impact structure property relationships. A combination of experimental and theoretical approaches are employed to investigate the SRO and LD in the prototype ESO, Mg0.2Co0.2Ni0.2Cu0.2Zn0.2O, generally referred to as J14. We demonstrate that the efficiency and accuracy of density functional theory (DFT) relaxed special quasirandom structures (SQS) enhances the analysis of the local structure of J14, unveiling the unique local cationic environments. Importantly, this joint experimental and computational approach sheds light on the understanding of local structure and structure property relationships in J14, demonstrating the necessity for further research into other high entropy and compositionally complex materials.

cond-mat.mtrl-sci↗

arXiv2022

What is in a Name: Defining -High Entropy- Oxides

High entropy oxides are emerging as an exciting new avenue to design highly tailored functional behaviors that have no traditional counterparts. Study and application of these materials are bringing together scientists and engineers from physics, chemistry, and materials science. The diversity of each of these disciplines comes with perspectives and jargon that may be confusing to those outside of the individual fields, which can result in miscommunication of important aspects of research. In this perspective, we provide examples of research and characterization taken from these different fields to provide a framework for classifying the differences between compositionally complex oxides, high entropy oxides, and entropy stabilized oxides, which is intended to bring a common language to this emerging area. We highlight the critical importance of understanding a materials crystallinity, composition, and mixing length scales in determining its true definition.

cond-mat.mtrl-sci↗

arXiv2020

Nanoscale degeneracy lifting in a geometrically frustrated antiferromagnet

The local atomic and magnetic structures of the compounds $A$MnO$_2$ ($A$ = Na, Cu), which realize a geometrically frustrated, spatially anisotropic triangular lattice of Mn spins, have been investigated by atomic and magnetic pair distribution function analysis of neutron total scattering data. Relief of frustration in CuMnO$_2$ is accompanied by a conventional cooperative symmetry-lowering lattice distortion driven by Néel order. In NaMnO$_2$, however, the distortion has a short-range nature. A cooperative interaction between the locally broken symmetry and short-range magnetic correlations lifts the magnetic degeneracy on a nanometer length scale, enabling long-range magnetic order in the Na-derivative. The degree of frustration, mediated by residual disorder, contributes to the rather differing pathways to a single, stable magnetic ground state in these two related compounds. This study demonstrates how nanoscale structural distortions that cause local-scale perturbations can lift the ground state degeneracy and trigger macroscopic magnetic order.

cond-mat.str-el↗

arXiv2019

Entropic elasticity and negative thermal expansion in a simple cubic crystal

While most solids expand when heated, some materials show the opposite behavior: negative thermal expansion (NTE). In polymers and biomolecules, NTE originates from the entropic elasticity of an ideal, freely-jointed chain. The origin of NTE in solids has been widely believed to be different. Our neutron scattering study of a simple cubic NTE material, ScF3, overturns this consensus. We observe that the correlation in the positions of the neighboring fluorine atoms rapidly fades on warming, indicating an uncorrelated thermal motion constrained by the rigid Sc-F bonds. This leads us to a quantitative theory of NTE in terms of entropic elasticity of a floppy network crystal, which is in remarkable agreement with experimental results. We thus reveal the formidable universality of the NTE phenomenon in soft and hard matter.

cond-mat.mtrl-sci↗

arXiv2019

Long range antiferromagnetic order in a rocksalt high entropy oxide

We report for the first time the magnetic structure of the high entropy oxide $(Mg_{0.2}Co_{0.2}Ni_{0.2}Cu_{0.2}Zn_{0.2})O$ using neutron powder diffraction. This material exhibits a sluggish magnetic transition but possesses a long-range ordered antiferromagnetic ground state, as revealed by DC and AC magnetic susceptibility, elastic and inelastic neutron scattering measurements. The magnetic propagation wavevector is k=(1/2, 1/2, 1/2) based on the cubic structure Fm-3m, and the magnetic structure consists of ferromagnetic sheets in the (111) planes with spins antiparallel between two neighboring planes. Inelastic neutron scattering reveals strong magnetic excitations at 100 K that survive up to room temperature. This work demonstrates that entropy-stabilized oxides represent a unique platform to study long range magnetic order with extreme chemical disorder.

cond-mat.mtrl-sci↗

arXiv2017

Quantum Griffiths phase inside the ferromagnetic phase of Ni$_{1-x}$V$_x$

We study by means of bulk and local probes the d-metal alloy Ni$_{1-x}$V$_x$ close to the quantum critical concentration, $x_c \approx 11.6\%$, where the ferromagnetic transition temperature vanishes. The magnetization-field curve in the ferromagnetic phase takes an anomalous power-law form with a nonuniversal exponent that is strongly $x$-dependent and mirrors the behavior in the paramagnetic phase. Muon spin rotation experiments demonstrate inhomogeneous magnetic order and indicate the presence of dynamic fluctuating magnetic clusters. These results provide strong evidence for a quantum Griffiths phase on the ferromagnetic side of the quantum phase transition.

cond-mat.str-el↗

arXiv2016

Verification of Anderson superexchange in MnO via magnetic pair distribution function analysis and \textit{ab initio} theory

We present temperature-dependent atomic and magnetic pair distribution function (PDF) analysis of neutron total scattering measurements of antiferromagnetic MnO, an archetypal strongly correlated transition-metal oxide. The known antiferromagnetic ground-state structure fits the low-temperature data closely with refined parameters that agree with conventional techniques, confirming the reliability of the newly developed magnetic PDF method. The measurements performed in the paramagnetic phase reveal significant short-range magnetic correlations on a $\sim$1~nm length scale that differ substantially from the low-temperature long-range spin arrangement. \textit{Ab initio} calculations using a self-interaction-corrected local spin density approximation of density functional theory predict magnetic interactions dominated by Anderson superexchange and reproduce the measured short-range magnetic correlations to a high degree of accuracy. Further calculations simulating an additional contribution from a direct exchange interaction show much worse agreement with the data. The Anderson superexchange model for MnO is thus verified by experiment and confirmed by \textit{ab initio} theory.

cond-mat.str-el↗

arXiv2014

Structural ground states of ($A,A'$)Cr$_2$O$_4$($A$=Mg, Zn; $A^{\prime}$ = Co, Cu) spinel solid solutions: Spin-Jahn-Teller and Jahn-Teller effects

We examine the effect of small amounts of magnetic substituents in the $A$ sites of the frustrated spinels MgCr$_2$O$_4$ and ZnCr$_2$O$_4$. Specifically we look for the effects of spin and lattice disorder on structural changes accompanying magnetic ordering in these compounds. Substitution of Co$^{2+}$ on the non-magnetic Zn$^{2+}$ site in Zn$_{1-x}$Co$_{x}$Cr$_2$O$_4$ where 0\,$<$\,$x$\,$\leq$\,0.2 completely suppresses the spin-Jahn-Teller distortion of ZnCr$_2$O$_4$ although these systems remain frustrated, and magnetic ordering occurs at very low temperatures of $T$\,$<$\,20\,K. On the other hand, the substitution of Jahn-Teller active Cu$^{2+}$ for Mg$^{2+}$ and Zn$^{2+}$ in Mg$_{1-x}$Cu$_{x}$Cr$_2$O$_4$ and Zn$_{1-x}$Cu$_{x}$Cr$_2$O$_4$ where 0\,$<$\,$x$\,$\leq$\,0.2 induce Jahn-Teller ordering at temperatures well above the Néel temperatures of these solid solutions, and yet spin interactions remain frustrated with long-range magnetic ordering occurring below 20\,K without any further lattice distortion. The Jahn-Teller distorted solid solutions Mg$_{1-x}$Cu$_{x}$Cr$_2$O$_4$ and Zn$_{1-x}$Cu$_{x}$Cr$_2$O$_4$ adopt the orthorhombic $Fddd$ structure of ferrimagnetic CuCr$_2$O$_4$. Total neutron scattering studies of Zn$_{1-x}$Cu$_{x}$Cr$_2$O$_4$ suggest that there are local $A$O$_4$ distortions in these Cu$^{2+}$-containing solid solutions at room temperature and that these distortions become cooperative when average structure distortions occur. Magnetism evolves from compensated antiferromagnetism in MgCr$_2$O$_4$ and ZnCr$_2$O$_4$ to uncompensated antiferromagnetism with substitution of magnetic cations on the non-magnetic cation sites of these frustrated compounds.

cond-mat.mtrl-sci↗

arXiv2009

Tuning magnetic frustration on the diamond lattice of the A-site magnetic spinels CoAl$_{2-x}$Ga$_x$O$_4$: Lattice expansion and site disorder

The spinels CoB$_2$O$_4$ with magnetic Co$^{2+}$ ions on the diamond lattice A site can be frustrated because of competing near-neighbor ($J_1$) and next-near neighbor ($J_2$) interactions. Here we describe attempts to tune the relative strengths of these interactions by substitution on the non-magnetic B-site. The system we employ is CoAl$_{2-x}$Ga$_x$O$_4$, where Al is systematically replaced by the larger Ga, ostensibly on the B site. As expected, Ga substitution expands the lattice, resulting in Co atoms on the A-site being pushed further from one other and thereby weakening magnetic interactions. In addition, Ga distributes between the B and the A site in a concentration dependent manner displacing an increasing amount of Co from the A site with increasing $x$. This increased inversion, which is confirmed by neutron diffraction studies carried out at room temperature, affects magnetic ordering very significantly, and changes the nature of the ground state. Modeling of the magnetic coupling illustrates the complexity that arises from the cation site disorder.

cond-mat.mtrl-sci↗

arXiv2008

Local structural origins of the distinct electronic properties of Nb-substituted SrTiO$_3$ and BaTi$O_3$

Near or less than 10% Nb substitution on the Ti site in perovskite SrTiO$_3$ results in metallic behavior, in contrast to what is seen in BaTiO$_3$. Given the nearly identical structure and electron counts of the two materials, the distinct ground states for low substitution have been a long-standing puzzle. Here we find from neutron studies of average and local structure, the subtle yet critical difference that we believe underpins the distinct electronic properties in these fascinating materials. While SrTi$_{0.875}$Nb_${0.125}$O$_3$ possesses a distorted non-cubic structure at 15 K, the BO$_6$ octahedra in the structure are regular. BaTi$_{0.875}$Nb$_{0.125}$O$_3$ on the other hand shows evidence for local cation off-centering whilst retaining a cubic structure.

cond-mat.mtrl-sci↗

arXiv2007

Local structure evolution in polycrystalline Zn$_{1-x}$Mg$_x$O ($0\leq{x}\leq{0.15}$) studied by Raman and by synchrotron x-ray pair distribution analysis

The local structures of Zn$_{1-x}$Mg$_x$O alloys have been studied by Raman spectroscopy and by synchrotron x-ray pair distribution function (PDF) analysis. Within the solid solution range ($0\leq{x}\leq{0.15}$) of Zn$_{1-x}$Mg$_x$O, the wurtzite framework is maintained with Mg homogeneously distributed throughout the wurtzite lattice. The $E_2^\mathrm{high}$ Raman line of Zn$_{1-x}$Mg$_x$O displays systematic changes in response to the evolution of the crystal lattice upon the Mg-substitution. The red-shift and broadening of the $E_2^\mathrm{high}$ mode are explained by the expansion of hexagonal $ab$-dimensions, and compositional disorder of Zn/Mg, respectively. Synchrotron x-ray PDF analyses of Zn$_{1-x}$Mg$_x$O reveal that the Mg atoms have a slightly reduced wurtzite parameter $u$ and more regular tetrahedral bond distances than the Zn atoms. For both Zn and Mg, the internal tetrahedral geometries are independent of the alloy composition.

cond-mat.mtrl-sci↗

arXiv2006

Synchrotron X-ray study of polycrystalline wurtzite Zn1-xMgxO (0 <= x <= 0.15): Evolution of crystal structure and polarization

The effect of Mg-substitution on the crystal structure of wurtzite ZnO is presented based on synchrotron X-ray diffraction studies of polycrystalline Zn1-xMgxO (0 <= x <= 0.15). Increase in Mg concentration results in pronounced c-axis compression of the hexagonal lattice, and in diminution of the off-center cation displacement within each tetrahedral ZnO4 unit. Going from ZnO to Zn0.85Mg0.15O, significant changes in the ionic polarization are observed (-5.6 to -4.8 uC/cm2), despite only subtle increments in the cell volume (~0.03 %) and the ab-area dimension (~0.1 %). The optical properties of the samples have also been characterized and the band gap changes from 3.24 eV (ZnO) to 3.35 eV (Zn0.85Mg0.15O).

cond-mat.mtrl-sci↗