Why is it that ABO 3 perovskites generally do not exhibit negative thermal expansion (NTE) over a wide temperature range, whereas layered perovskites of the same chemical family often do? It is generally accepted that there are two key ingredients that determine the extent of NTE: the presence of soft phonon modes that drive contraction (have negative Grüneisen parameters); and anisotropic elastic compliance that predisposes the material to the deformations required for NTE along a specific axis. This difference in thermal expansion properties is surprising since both ABO 3 and layered perovskites often possess these ingredients in equal measure in their high-symmetry phases. Using first principles calculations and symmetry analysis, we show that in layered perovskites there is a significant enhancement of elastic anisotropy due to symmetry breaking that results from the combined effect of layering and condensed rotations of oxygen octahedra. This feature, unique to layered perovskites of certain symmetry, is what allows uniaxial NTE to persist over a large temperature range. This fundamental insight means that symmetry and the elastic tensor can be used as descriptors in high-throughput screening and to direct materials design.

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By tuning the tolerance factor, t, of the Ruddlesden-Popper oxide Ca 2 MnO 4 through isovalent substitutions, we show that the uniaxial coefficient of linear thermal expansion (CLTE) of these systems can be systematically changed through large negative to positive values. Highresolution X-ray diffraction measurements show that the magnitude of uniaxial negative thermal expansion (NTE) increases as t decreases across the stability window of the NTE phase.

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Background There is an increasing number of paediatric and adolescent patients being diagnosed with Inflammatory Bowel Disease (IBD) 1. Being diagnosed at an early age can have a detrimental effect on a child’s development, so the need for support is vital. Adult experiences of living with IBD are known 2 , but very little is known about paediatric experiences. This literature review aimed to identify the paediatric and adolescent experiences of living with IBD and explore how IBD impacts their life. Methods A search was performed on following databases: Medline, CINAHL, and British Nursing Index. The inclusion criteria were: IBD, age under 18 years old, English language, primary qualitative research, and a publication date between 2016-2021. Out of the 43 papers identified, only three were selected as they met the inclusion/exclusion criteria. A qualitative synthesis of evidence was conducted, and the data was reinterpreted 3. Results Among the three papers, there was a dominant theme about the ‘Fear of not being accepted'. This overarching theme revolved around peer acceptance, and included two main themes: ‘Fear of disclosure' and 'How do I fit in?', as patients did not want to disclose their condition and expressed their desire to be viewed as normal. Throughout their experiences, children and adolescents expressed embarrassment as the primary feeling since living with IBD. Having IBD as a child or adolescent could adversely affect their psycho-social development, especially during their sexual development, affecting their romantic relationships and interactions with other people. The fear of not being accepted led participants to feel unattractive and apprehensive when forming new relationships. Conclusion It is imperative for children and adolescents to feel accepted, to feel comfortable disclosing their illness, and to feel equal to their peers. Children and adolescents face a variety of psycho- socio- emotional challenges living with IBD. Due to the limited number of studies that have explored the challenges that paediatrics and adolescents encounter, the need for more evidence is crucial. More evidence on children experiences of living with IBD would help healthcare professionals understand the impact of illness, and develop strategies to support children and adolescents living with IBD to minimise the fear of social stigma and rejection. 1. Kaplan GG. The global burden of IBD: from 2015 to 2025. Nat Rev Gastroenterol Hepatol. 2015;12(12). 2. Fourie S, Jackson D, Aveyard H. Living with Inflammatory Bowel Disease: A review of qualitative research studies. Int J Nurs Stud. 2018;87:149-156. 3. Thomas J ;Harden A. Methods for the Thematic Synthesis of Qualitativeresearch in Sistematic Reviews.; 2007.

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