Variable dimensionality in 'hollow' hybrid tin iodide perovskites

We acknowledge support from the University of St Andrews and the Leverhulme trust (RPG-2018-065).Two ‘hollow’ B-site deficient perovskites, (TzH)11(H3PO2)Sn6I23 and (TzH)3Sn2I7 (TzH+ = 1,2,4-triazolium, H3PO2 = hypohosphorous acid), have been prepared. (TzH)11(H3PO2)Sn6I23 is the first example of a 2D layered structure of this type. Leaving the same reaction mixture for an extended time also affords the 3D derivative (TzH)3Sn2I7.Publisher PDFPeer reviewe

AMP!: A Cross-site Analysis of the Effects of a Theater-based Intervention on Adolescent Awareness, Attitudes, and Knowledge about HIV

AMP! (Arts-based, Multiple component, Peer-education) is an HIV intervention developed for high school adolescents. AMP! uses interactive theater-based scenarios developed by trained college undergraduates to deliver messages addressing HIV/STI prevention strategies, healthy relationships, and stigma reduction towards people living with HIV/AIDS. We used a pre-test/post-test, control group study design to simultaneously assess intervention effect on ninth grade students in an urban county in California (N = 159) and a suburban county in North Carolina (N = 317). In each location, the control group received standard health education curricula delivered by teachers; the intervention group received AMP! in addition to standard health education curricula. Structural equation modeling was used to determine intervention effects. The post-test sample was 46% male, 90% self-identified as heterosexual, 32% reported receiving free or reduced lunch, and 49% White. Structural models indicated that participation in AMP! predicted higher scores on HIV knowledge (p = .05), HIV awareness (p = .01), and HIV attitudes (p = .05) at the post-test. Latent means comparison analyses revealed post-test scores were significantly higher than pre-test scores on HIV knowledge (p = .001), HIV awareness (p = .001), and HIV attitudes (p = .001). Further analyses indicated that scores rose for both groups, but the post-test scores of intervention participants were significantly higher than controls (HIV knowledge (p = .01), HIV awareness (p = .01), and HIV attitudes (p = .05)). Thus, AMP!’s theater-based approach shows promise for addressing multiple adolescent risk factors and attitudes concerning HIV in school settings

A hybrid fluoride layered perovskite, (enH2)MnF4

We acknowledge the University of St Andrews and the China Scholarship Council (studentship to TL) and the EPSRC (DTG: EP/K503162/1) for a studentship (to RC). The are no conflicts of interest to declare.The title compound is the first example of a layered fluoroperovskite containing an interlayer organic cation. Preliminary magnetic characterisation is reported, and structural relationships to related layered perovskites are discussed.PostprintPostprintPeer reviewe

EU development policy: evolving as an instrument of foreign policy and as an expression of solidarity

This article introduces the special issue on the evolution of European Union development policy, against the background of fundamental challenges that have emerged since the 2009 Lisbon Treaty. The special issue's objective is to highlight the complex dynamics of a policy area that is called on to address the massive challenges of poverty, inequality, healthcare capacity, climate change, insecurity and weak governance in countries of the global south, and at the same time support European foreign policy objectives including political stability, migration management, access to resources and markets. In this introductory article, we attempt to sketch the broad outlines of the conceptual and practical dilemmas faced by a policy area that is supposed to be able to fix almost any problem. We observe that European development policy's evolution is driven by the tension between its raison d'etre as a concrete expression of global solidarity and international cooperation, and its increasing instrumentalisation in the service of European economic and security interests. We highlight some of the key challenges that have emerged in the last decade, including rising populist nationalism and Brexit within Europe, the changing nature of relationships between Europe and countries who receive EU aid, and the changing nature of development cooperation itself, exemplified by the 2030 Agenda and the Sustainable Development Goals. We outline the specific contributions the articles in this special issue make to research and policy debates on the themes we raise in this introduction. We conclude that the battle between the forces of solidarity and instrumentality has evolved EU development policy into an impossibly complex arena of competing norms, practices and institutions, which raises many open questions for future research

Octahedral tilting in the polar hexagonal tungsten bronzes RbNbW2O9 and KNbW2O9

We thank the Science and Technology Facilities Council (STFC) for the provision of neutron diffraction facilities at ISIS (HRPD experiment RB1710021, doi: 10.5286/ISIS.E.RB1710021) and the School of Chemistry, University of St Andrews for funding of a studentship to JAM through the EPSRC doctoral training grant (EP/K503162/1).The ambient temperature structures (orthorhombic, space group, Cmc21) of the polar hexagonal tungsten bronzes RbNbW2O9 and KNbW2O9 have been determined by high-resolution powder neutron diffraction. Displacement of the A-site cation in the polar c-axis, with concomitant octahedral tilting, occurs to optimise the A-cation bonding environment reducing the coordination from 18 to 16. This effect is more evident in KNbW2O9 due to decreased A-cation size. The octahedral tilting in both compositions results in a doubling of the c-axis that has not previously been reported, highlighting the importance of neutron diffraction as a complementary technique for structural determination of such systems.Publisher PDFPeer reviewe

Polar ferromagnet induced by fluorine positioning in isomeric layered copper halide perovskites

We acknowledge the University of St Andrews and the China Scholarship Council (studentship to CH) and the University of St Andrews (studentship to AJB).We present the influence of positional isomerism on the crystal structure of fluorobenzylammonium copper (II) chloride perovskites A2CuCl4, by incorporating ortho, meta and para- fluorine substitution in the benzylamine structure. Two-dimensional (2D) polar ferromagnet (3-FbaH)2CuCl4 (3-FbaH+ = 3-fluorobenzylammonium) is successfully obtained, which crystallizes in a polar orthorhombic space group Pca21 at room temperature. In contrast, both (2-FbaH)2CuCl4 (2-FbaH+ = 2-fluorobenzylammonium) and (4-FbaH)2CuCl4 (4-FbaH+ = 4-fluorobenzylammonium) crystallize in centrosymmetric space groups P21/c and Pnma at room temperature, respectively, displaying significant differences in crystal structures. These differences indicate that the position of the fluorine atom is a driver for the polar behaviour in (3-FbaH)2CuCl4. Preliminary magnetic measurements confirm that these three perovskites possess dominant ferromagnetic interactions within the inorganic [CuCl4]∞ layers. Therefore, (3-FbaH)2CuCl4 is a polar ferromagnet, with potential as a type I multiferroic. This work is expected to promote further development of high performance 2D copper (II) halide perovskite multiferroic materials.Publisher PDFPeer reviewe

Structure-directing effects in (110)-layered hybrid perovskites containing two distinct organic moieties

We acknowledge support from the University of St Andrews, the China Scholarship Council (studentship to YYG) and the Leverhulme trust (RPG-2018-065).The hybrid perovskites (ImH)(GuH)PbBr4 and (TzH)(GuH)PbBr4 (ImH+ = imidazolium, GuH+ = guanidinium, TzH+ = 1,2,4-triazolium) both adopt (110)-oriented layer structures. However, the GuH+ cation adopts differing crystallographic sites in the two structures (intra-layer versus inter-layer); this is discussed in terms of the sizes of the organic cations and their hydrogen-bonding preferences.PostprintPeer reviewe

‘I learned to be okay with talking about sex and safety’: assessing the efficacy of a theatre-based HIV prevention approach for adolescents in North Carolina

Adolescents are at increased risk of HIV and sexually transmitted infections (STIs) in the Southern states of the USA, where rates among youth are higher than in the rest of the nation. This paper reports on findings from a pilot study of an HIV prevention intervention that uses interactive theatre to educate young people about sexual health. The intervention was developed in Los Angeles and adapted for testing in the South of the USA, with its legacy of abstinence-based approaches to sexual health education. This study assessed intervention effects among a sample of young people in two public high schools in North Carolina. We used a pre-test, post-test quasi-experimental evaluation design to assess changes in 317 ninth grade participants’ knowledge and attitudes about HIV. At post-test, we found statistically significant increases in participants’ HIV knowledge (t= 60.14; p=.001), as well as changes in attitudes (X2=8.23; p=.042) and awareness (X2=4.94; p=.026). Focus group data corroborated increase in HIV knowledge and reduction in HIV stigma as successful outcomes of intervention participation. The findings make an important contribution to the literature on theatre-based interventions for sexual health education. Furthermore, they highlight the importance of considering socio-cultural and political context in implementing HIV prevention interventions in schools

Unexpected phase transition sequence in the ferroelectric Bi4Ti3O12

Authors thank Dr George Carins for experimental assistance. Y.-Y.G thanks the China Scholarships Council and the University of St Andrews for a studentship.The high-temperature phase behaviour of the ferroelectric layered perovskite Bi4Ti3O12 has been re-examined by high-resolution powder neutron diffraction. Previous studies, both experimental and theoretical, had suggested conflicting structural models and phase transition sequences, exacerbated by the complex interplay of several competing structural instabilities. Here, we confirm that Bi4Ti3O12 undergoes two separate structural transitions from the aristotype tetragonal phase (space group I4/mmm) to the ambient temperature ferroelectric phase (confirmed as monoclinic, B1a1). An unusual, and previously unconsidered, intermediate paraelectric phase is suggested to exist above TC, with tetragonal symmetry, space group P4/mbm. This phase is peculiar in displaying a unique type of octahedral tilting, in which the triple perovskite blocks of the layered structure alternate between tilted and untilted. This is rationalised in terms of the bonding requirements of the Bi3+ cations within the perovskite blocks.Publisher PDFPeer reviewe