F igure 4. The cavity sites of ( a ) burtite and ( b ) stottite. The two upper figures show the same site in burtite viewed from two directions. The two lower figures show the burtite-like cavity in stotitte (left) and the highly distorted cavity (right). O-H···O linkages for burtite

F ig . 5. The cavity sites of burtite and stottite. The two upper figures show the same site in burtite viewed from two directions. The two lower figures show the burtite-like cavity 1 (left) and the highly-distorted cavity 2 (right). O–H...O linkages are shown for burtite and their analogous

F ig . 5. The cavity sites of burtite and stottite. The two upper figures show the same site in burtite viewed from two directions. The two lower figures show the burtite-like cavity 1 (left) and the highly-distorted cavity 2 (right). O–H...O linkages are shown for burtite and their analogous

F ig . 5. The cavity sites of burtite and stottite. The two upper figures show the same site in burtite viewed from two directions. The two lower figures show the burtite-like cavity 1 (left) and the highly-distorted cavity 2 (right). O–H...O linkages are shown for burtite and their analogous

F ig . 1. ( a ) The structural motif of hydroxide-perovskites anticipated in a first century Roman mosaic from Ostia, Italy. ( b ) The structure of burtite, CaSn(OH) 6 , ( Basciano et al. , 1998 ), space group Pn 3İ; O–H…O linkages across the faces of the vacant A site are shown. Burtite has

F ig . 2. The hydrogen-bonded O–H...O linkages in schoenfliesite, MgSn(OH) 6 , and burtite, CaSn(OH) 6 .

Fig. 22. The hydrogen-bonding topology of burtite, CaSn(OH) 6 . The isolated ring comprises four O–H···O bridges, having O···O distances of 2.8 and 3.0 Å. H···H distances are indicated. Isolated four-membered rings are characteristic of all cubic hydroxide perovskites. The lower diagrams

Fig. 22. The hydrogen-bonding topology of burtite, CaSn(OH) 6 . The isolated ring comprises four O–H···O bridges, having O···O distances of 2.8 and 3.0 Å. H···H distances are indicated. Isolated four-membered rings are characteristic of all cubic hydroxide perovskites. The lower diagrams

Fig. 22. The hydrogen-bonding topology of burtite, CaSn(OH) 6 . The isolated ring comprises four O–H···O bridges, having O···O distances of 2.8 and 3.0 Å. H···H distances are indicated. Isolated four-membered rings are characteristic of all cubic hydroxide perovskites. The lower diagrams

F ig . 1. Octahedral topologies of burtite ( a + a + a + ) and stottite ( a + a + c − ). The effect of the reversed [001] rotation is shown at bottom right. A single cavity corresponding to 1/8 of the unit cell ( a /2, c /2) is shown in each case.

F ig . 4. Plot of the normalized cell volume of burtite, V P / V 0 , against pressure. The fit to a second-order Birch-Murnaghan equation of state is shown ( K 0 = 47.4 GPa). Error bars on data-points are 2σ. Pressure uncertainties are smaller than symbol widths. The compression curve

F ig . 6. The hydrogen-bonding (O–H...O) network of burtite. Hydrogen atoms are shown as red (H1) and blue (H2) circles. ( a ) <111> view. The ‘petals’ are the four-membered rings of O–H...O linkages. ( b ) Oblique view of ( a ) showing the environment around the 3̅ centre. Hydroxyl bonds

F ig . 3. Background-subtracted X-ray powder diffraction pattern and Rietveld refinement of synthetic deuterated burtite, CaSn(OD) 6 , determined at 2.95 GPa. This is a typical example of the data collected and refined in this study. The data are red crosses. Reflection markers and a difference

and burtite, all of which have only isolated rings. In these three phases there are two ½-occupied H sites.

lakargiite overgrowing a porous aggregate of lakargiite and srebrodolskite from the chegemite zone of xenolith no. 7; ( e ) crystals of high-Sn lakargiite with external zones of megawite growing over a fine-grained lakargiite-wadalite-hibschite aggregate, burtite CaSn(OH) 6 also occurs in this association